Web service
Encyclopedia
The W3C defines a "Web service" as "a software system designed to support interoperable
Interoperability
Interoperability is a property referring to the ability of diverse systems and organizations to work together . The term is often used in a technical systems engineering sense, or alternatively in a broad sense, taking into account social, political, and organizational factors that impact system to...
machine-to-machine interaction over a network
Computer network
A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....
". It has an interface described in a machine-processable format (specifically Web Services Description Language, known by the acronym WSDL
Web Services Description Language
The Web Services Description Language is an XML-based language that is used for describing the functionality offered by a Web service. A WSDL description of a web service provides a machine-readable description of how the service can be called, what parameters it expects and what data structures...
). Other systems interact with the Web service in a manner prescribed by its description using SOAP
SOAP
SOAP, originally defined as Simple Object Access Protocol, is a protocol specification for exchanging structured information in the implementation of Web Services in computer networks...
messages, typically conveyed using HTTP with an XML serialization in conjunction with other Web-related standards."
The W3C also states, "We can identify two major classes of Web services, REST
Representational State Transfer
Representational state transfer is a style of software architecture for distributed hypermedia systems such as the World Wide Web. The term representational state transfer was introduced and defined in 2000 by Roy Fielding in his doctoral dissertation...
-compliant Web services, in which the primary purpose of the service is to manipulate XML representations of Web resources using a uniform set of "stateless" operations; and arbitrary Web services, in which the service may expose an arbitrary set of operations."
Big Web services
"Big Web services" use Extensible Markup LanguageXML
Extensible Markup Language is a set of rules for encoding documents in machine-readable form. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards....
(XML) messages that follow the SOAP
SOAP
SOAP, originally defined as Simple Object Access Protocol, is a protocol specification for exchanging structured information in the implementation of Web Services in computer networks...
standard and have been popular with traditional enterprises. In such systems, there is often a machine-readable description of the operations offered by the service written in the Web Services Description Language
Web Services Description Language
The Web Services Description Language is an XML-based language that is used for describing the functionality offered by a Web service. A WSDL description of a web service provides a machine-readable description of how the service can be called, what parameters it expects and what data structures...
(WSDL). The latter is not a requirement of a SOAP endpoint, but it is a prerequisite for automated client-side
Client-side
Client-side refers to operations that are performed by the client in a client–server relationship in a computer network.Typically, a client is a computer application, such as a web browser, that runs on a user's local computer or workstation and connects to a server as necessary...
code generation in many Java
Java (programming language)
Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...
and .NET
.NET Framework
The .NET Framework is a software framework that runs primarily on Microsoft Windows. It includes a large library and supports several programming languages which allows language interoperability...
SOAP frameworks (frameworks such as Apache Axis2
Apache Axis2
Apache Axis2 is a core engine for Web services. It is a complete re-design and re-write of the widely used Apache Axis SOAP stack. Implementations of Axis2 are available in Java and C....
, Apache CXF
Apache CXF
Apache CXF is an open-source, fully featured Web services framework. It originated as the combination of two open-source projects: Celtix developed by IONA Technologies and XFire developed by a team hosted at Codehaus. These two projects were combined by people working together at the Apache...
, and Spring being notable exceptions). Some industry organizations, such as the WS-I
Web Services Interoperability
The Web Services Interoperability Organization is an industry consortium chartered to promote interoperability amongst the stack of web services specifications. WS-I does not define standards for web services; rather, it creates guidelines and tests for interoperability...
, mandate both SOAP and WSDL in their definition of a Web service.
Web API
Web api
A web API is typically a defined set of HTTP request messages along with a definition of the structure of response messages, typically expressed in JSON or XML...
is a development in Web services (in a movement called Web 2.0
Web 2.0
The term Web 2.0 is associated with web applications that facilitate participatory information sharing, interoperability, user-centered design, and collaboration on the World Wide Web...
) where emphasis has been moving away from SOAP
SOAP
SOAP, originally defined as Simple Object Access Protocol, is a protocol specification for exchanging structured information in the implementation of Web Services in computer networks...
based services towards representational state transfer
Representational State Transfer
Representational state transfer is a style of software architecture for distributed hypermedia systems such as the World Wide Web. The term representational state transfer was introduced and defined in 2000 by Roy Fielding in his doctoral dissertation...
(REST) based communications. REST services do not require XML, SOAP, or WSDL
Web Services Description Language
The Web Services Description Language is an XML-based language that is used for describing the functionality offered by a Web service. A WSDL description of a web service provides a machine-readable description of how the service can be called, what parameters it expects and what data structures...
service-API definitions.
Web APIs allow the combination of multiple Web services into new applications known as mashup
Mashup (web application hybrid)
In Web development, a mashup is a Web page or application that uses and combines data, presentation or functionality from two or more sources to create new services...
s.
When used in the context of Web development
Web development
Web development is a broad term for the work involved in developing a web site for the Internet or an intranet . This can include web design, web content development, client liaison, client-side/server-side scripting, web server and network security configuration, and e-commerce development...
, Web API is typically a defined set of Hypertext Transfer Protocol (HTTP
Hypertext Transfer Protocol
The Hypertext Transfer Protocol is a networking protocol for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web....
) request messages along with a definition of the structure of response messages, usually expressed in an Extensible Markup Language (XML
XML
Extensible Markup Language is a set of rules for encoding documents in machine-readable form. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards....
) or JavaScript Object Notation (JSON
JSON
JSON , or JavaScript Object Notation, is a lightweight text-based open standard designed for human-readable data interchange. It is derived from the JavaScript scripting language for representing simple data structures and associative arrays, called objects...
) format.
When running composite Web services, each sub service can be considered autonomous. The user has no control over these services. Also the Web services themselves are not reliable; the service provider may remove, change or update their services without giving notice to users. The reliability and fault tolerance is not well supported; faults may happen during the execution. Exception handling in the context of Web services is still an open research issue, although this can still be handled by responding with an error object to the clients.
Styles of use
Web services are a set of tools that can be used in a number of ways. The three most common styles of use are RPCRemote procedure call
In computer science, a remote procedure call is an inter-process communication that allows a computer program to cause a subroutine or procedure to execute in another address space without the programmer explicitly coding the details for this remote interaction...
, SOA
Service-oriented architecture
In software engineering, a Service-Oriented Architecture is a set of principles and methodologies for designing and developing software in the form of interoperable services. These services are well-defined business functionalities that are built as software components that can be reused for...
and REST
Representational State Transfer
Representational state transfer is a style of software architecture for distributed hypermedia systems such as the World Wide Web. The term representational state transfer was introduced and defined in 2000 by Roy Fielding in his doctoral dissertation...
.
Remote procedure calls
RPC Web services present a distributed function (or method) call interface that is familiar to many developers. Typically, the basic unit of RPC Web services is the WSDL operation.
The first Web services tools were focused on RPC, and as a result this style is widely deployed and supported. However, it is sometimes criticized for not being loosely coupled
Loose coupling
In computing and systems design a loosely coupled system is one where each of its components has, or makes use of, little or no knowledge of the definitions of other separate components. The notion was introduced into organizational studies by Karl Weick...
, because it was often implemented by mapping services directly to language-specific functions or method calls. Many vendors felt this approach to be a dead end, and pushed for RPC to be disallowed in the WS-I Basic Profile
WS-I Basic Profile
The WS-I Basic Profile , a specification from the Web Services Interoperability industry consortium , provides interoperability guidance for core Web Services specifications such as SOAP, WSDL, and UDDI...
.
Other approaches with nearly the same functionality as RPC are: Object Management Group
Object Management Group
Object Management Group is a consortium, originally aimed at setting standards for distributed object-oriented systems, and is now focused on modeling and model-based standards.- Overview :...
's (OMG) Common Object Request Broker Architecture (CORBA
Common Object Request Broker Architecture
The Common Object Request Broker Architecture is a standard defined by the Object Management Group that enables software components written in multiple computer languages and running on multiple computers to work together .- Overview:CORBA enables separate pieces of software written in different...
), Open Software Foundation
Open Software Foundation
The Open Software Foundation was a not-for-profit organization founded in 1988 under the U.S. National Cooperative Research Act of 1984 to create an open standard for an implementation of the UNIX operating system.-History:...
's (OSF) DCE/RPC
DCE/RPC
DCE/RPC, short for "Distributed Computing Environment / Remote Procedure Calls", is the remote procedure call system developed for the Distributed Computing Environment...
, Microsoft
Microsoft
Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
's RPC (a part of DCOM
Distributed component object model
Distributed Component Object Model is a proprietary Microsoft technology for communication among software components distributed across networked computers. DCOM, which originally was called "Network OLE", extends Microsoft's COM, and provides the communication substrate under Microsoft's COM+...
) or .NET Remoting
.NET Remoting
.NET Remoting is a Microsoft application programming interface for interprocess communication released in 2002 with the 1.0 version of .NET Framework. It is one in a series of Microsoft technologies that began in 1990 with the first version of Object Linking and Embedding for 16-bit Windows...
and Sun Microsystems
Sun Microsystems
Sun Microsystems, Inc. was a company that sold :computers, computer components, :computer software, and :information technology services. Sun was founded on February 24, 1982...
's Java/Remote Method Invocation (RMI
Java remote method invocation
The Java Remote Method Invocation Application Programming Interface , or Java RMI, is a Java application programming interface that performs the object-oriented equivalent of remote procedure calls ....
).
Service-oriented architecture
Web services can also be used to implement an architecture according to service-oriented architecture (SOA) concepts, where the basic unit of communication is a message, rather than an operation. This is often referred to as "message-orientedMessage-oriented middleware
Message-oriented middleware is software or hardware infrastructure supporting sending and receiving messages between distributed systems. MOM allows application modules to be distributed over heterogeneous platforms and reduces the complexity of developing applications that span multiple...
" services.
SOA Web services are supported by most major software vendors and industry analysts. Unlike RPC Web services, loose coupling
Loose coupling
In computing and systems design a loosely coupled system is one where each of its components has, or makes use of, little or no knowledge of the definitions of other separate components. The notion was introduced into organizational studies by Karl Weick...
is more likely, because the focus is on the "contract" that WSDL provides, rather than the underlying implementation details.
Middleware analyst
Middleware analyst
Middleware analysts are computer software engineers with a specialization in products that connect two different computer systems together. These products can be open-source or proprietary...
s use enterprise service bus
Enterprise service bus
An enterprise service bus is a software architecture model used for designing and implementing the interaction and communication between mutually interacting software applications in Service Oriented Architecture...
es (ESBs) that combine message-oriented
Message-oriented middleware
Message-oriented middleware is software or hardware infrastructure supporting sending and receiving messages between distributed systems. MOM allows application modules to be distributed over heterogeneous platforms and reduces the complexity of developing applications that span multiple...
processing and Web services to create an event-driven SOA
Event-driven SOA
Event-driven SOA is a form of service-oriented architecture , combining the intelligence and proactiveness of event-driven architecture with the organizational capabilities found in service offerings...
. Examples of open-source ESB are Mule
Mule (software)
Mule is a lightweight enterprise service bus and integration framework. It can handle services and applications using disparate transport and messaging technologies...
and Open ESB
Open ESB
Open ESB is a Java based open source enterprise service bus. Open ESB can be used as a platform for both Enterprise Application Integration and SOA. Open ESB is built on open standards....
. An alternate approach is the Hub-and-Spoke model, which is server based. An example of this is Enterprise Message Service (EMS, an implementation of JMS).
Representational state transfer (REST)
REST attempts to describe architectures that use HTTP or similar protocols by constraining the interface to a set of well-known, standard operations (like GET, POST, PUT, DELETE for HTTP). Here, the focus is on interacting with statefulState (computer science)
In computer science and automata theory, a state is a unique configuration of information in a program or machine. It is a concept that occasionally extends into some forms of systems programming such as lexers and parsers....
resources, rather than messages or operations. Clean URLs are tightly associated with the REST concept.
An architecture based on REST (one that is 'RESTful') can use WSDL to describe SOAP messaging over HTTP, can be implemented as an abstraction purely on top of SOAP (e.g., WS-Transfer), or can be created without using SOAP at all.
WSDL version 2.0
Web Services Description Language
The Web Services Description Language is an XML-based language that is used for describing the functionality offered by a Web service. A WSDL description of a web service provides a machine-readable description of how the service can be called, what parameters it expects and what data structures...
offers support for binding to all the HTTP request methods (not only GET and POST as in version 1.1) so it enables a better implementation of RESTful web service
Representational State Transfer
Representational state transfer is a style of software architecture for distributed hypermedia systems such as the World Wide Web. The term representational state transfer was introduced and defined in 2000 by Roy Fielding in his doctoral dissertation...
s. However, support for this specification is still poor in software development kit
Software development kit
A software development kit is typically a set of software development tools that allows for the creation of applications for a certain software package, software framework, hardware platform, computer system, video game console, operating system, or similar platform.It may be something as simple...
s, which often offer tools only for WSDL 1.1.
Automated design methodologies
Automated tools can aid in the creation of a Web service. For services using WSDL it is possible to either automatically generate WSDL for existing classes (a bottom-up strategy) or to generate a class skeleton given existing WSDL (a top-down strategy).- A developer using a bottom up method writes implementing classes first (in some programming language), and then uses a WSDL generating tool to expose methods from these classes as a Web service. This is often the simpler approach.
- A developer using a top down method writes the WSDL document first and then uses a code generating tool to produce the class skeleton, to be completed as necessary. This way is generally considered more difficult but can produce cleaner designs
Criticisms
Critics of non-RESTful Web services often complain that they are too complex and based upon large software vendors or integrators, rather than typical open sourceOpen source
The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...
implementations. There are open source implementations like Apache Axis
Apache Axis
Apache Axis is an open source, XML based Web service framework. It consists of a Java and a C++ implementation of the SOAP server, and various utilities and APIs for generating and deploying Web service applications. Using Apache Axis, developers can create interoperable, distributed computing...
and Apache CXF
Apache CXF
Apache CXF is an open-source, fully featured Web services framework. It originated as the combination of two open-source projects: Celtix developed by IONA Technologies and XFire developed by a team hosted at Codehaus. These two projects were combined by people working together at the Apache...
.
One key concern of the REST Web service developers is that the SOAP WS toolkits make it easy to define new interfaces for remote interaction, often relying on introspection to extract the WDL, since a minor change on the server (even an upgrade of the SOAP stack) can result in different WSDL and a different service interface. The client-side classes that can be generated from WSDL and XSD descriptions of the service are often similarly tied to a particular version of the SOAP endpoint and can break, if the endpoint changes or the client-side SOAP stack is upgraded. Well-designed SOAP endpoints (with handwritten XSD and WSDL) do not suffer from this but there is still the problem that a custom interface for every service requires a custom client for every service.
There are also concerns about performance due to Web services' use of XML as a message format and SOAP/HTTP in enveloping and transport.
See also
- Amazon Web ServicesAmazon Web ServicesAmazon Web Services is a collection of remote computing services that together make up a cloud computing platform, offered over the Internet by Amazon.com...
- Business Intelligence 2.0Business Intelligence 2.0Business Intelligence 2.0 is a term that refers to new tools and software for business intelligence, beginning in the mid-2000s, that enable, among other things, dynamic querying of real-time corporate data by employees, and a more web- and browser-based approached to such data, as opposed to the...
(BI 2.0) - Devices Profile for Web ServicesDevices Profile for Web ServicesThe Devices Profile for Web Services defines a minimal set of implementation constraints to enable secure Web Service messaging, discovery, description, and eventing on resource-constrained devices....
- Enterprise Information IntegrationEnterprise Information IntegrationEnterprise Information Integration , is a process of information integration, using data abstraction to provide a unified interface for viewing all the data within an organization, and a single set of structures and naming conventions to represent this data; the goal of EII is to get a large set of...
(EII) - List of web service frameworks
- List of web service specifications
- Microsoft Connected Services Framework
- OAuthOAuthOAuth is an open standard for authorization. It allows users to share their private resources stored on one site with another site without having to hand out their credentials, typically username and password.OAuth allows users to hand out tokens instead of credentials to their data hosted by a...
- Service Implementation BeanService Implementation BeanA Service Implementation Bean , is a term used in Java Platform, Enterprise Edition, for a Java object implementing a web service. It can be either a POJO or a Stateless Session EJB. The Java interface of an SIB is called a Service Endpoint Interface .-External links:*...
- Service systemService systemA service system is a configuration of technology and organizational networks designed to deliver services that satisfy the needs, wants, or aspirations of customers.- Scope of the term :...
- Service-oriented architectureService-oriented architectureIn software engineering, a Service-Oriented Architecture is a set of principles and methodologies for designing and developing software in the form of interoperable services. These services are well-defined business functionalities that are built as software components that can be reused for...
(SOA) - SOAPjrSOAPjrSOAPjr is a protocol specification for exchanging structured information in the implementation of Web services in computer networks. It is a hybrid of SOAP and JSON-RPC .-Introduction:...
- Web Processing ServiceWeb Processing ServiceThe OGC Web Processing Service Interface Standard provides rules for standardizing how inputs and outputs for invoking geospatial processing services, such as polygon overlay, as a Web service. The WPS standard defines how a client can request the execution of a process, and how the output from...
- Web serverWeb serverWeb server can refer to either the hardware or the software that helps to deliver content that can be accessed through the Internet....
- Web Services DiscoveryWeb Services DiscoveryWeb services provide access to software systems over the Internet using standard protocols. In a minimalistic scenario there exists at least a Web service provider that publishes some service such as a weather service and a Web service consumer that uses this service...
External links
- Messaging Design Pattern and a distributed component/service model
- W3C Web Services Activity home page
- Web Services Architecture (W3C Working Group Note)
- Where to find Web Services on the Web: Investigating Web Services on the World Wide Web (2008)
The W3C defines a "Web service" as "a software system designed to support interoperable
Interoperability
Interoperability is a property referring to the ability of diverse systems and organizations to work together . The term is often used in a technical systems engineering sense, or alternatively in a broad sense, taking into account social, political, and organizational factors that impact system to...
machine-to-machine interaction over a network
Computer network
A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....
". It has an interface described in a machine-processable format (specifically Web Services Description Language, known by the acronym WSDL
Web Services Description Language
The Web Services Description Language is an XML-based language that is used for describing the functionality offered by a Web service. A WSDL description of a web service provides a machine-readable description of how the service can be called, what parameters it expects and what data structures...
). Other systems interact with the Web service in a manner prescribed by its description using SOAP
SOAP
SOAP, originally defined as Simple Object Access Protocol, is a protocol specification for exchanging structured information in the implementation of Web Services in computer networks...
messages, typically conveyed using HTTP with an XML serialization in conjunction with other Web-related standards."
The W3C also states, "We can identify two major classes of Web services, REST
Representational State Transfer
Representational state transfer is a style of software architecture for distributed hypermedia systems such as the World Wide Web. The term representational state transfer was introduced and defined in 2000 by Roy Fielding in his doctoral dissertation...
-compliant Web services, in which the primary purpose of the service is to manipulate XML representations of Web resources using a uniform set of "stateless" operations; and arbitrary Web services, in which the service may expose an arbitrary set of operations."
Big Web services
"Big Web services" use Extensible Markup LanguageXML
Extensible Markup Language is a set of rules for encoding documents in machine-readable form. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards....
(XML) messages that follow the SOAP
SOAP
SOAP, originally defined as Simple Object Access Protocol, is a protocol specification for exchanging structured information in the implementation of Web Services in computer networks...
standard and have been popular with traditional enterprises. In such systems, there is often a machine-readable description of the operations offered by the service written in the Web Services Description Language
Web Services Description Language
The Web Services Description Language is an XML-based language that is used for describing the functionality offered by a Web service. A WSDL description of a web service provides a machine-readable description of how the service can be called, what parameters it expects and what data structures...
(WSDL). The latter is not a requirement of a SOAP endpoint, but it is a prerequisite for automated client-side
Client-side
Client-side refers to operations that are performed by the client in a client–server relationship in a computer network.Typically, a client is a computer application, such as a web browser, that runs on a user's local computer or workstation and connects to a server as necessary...
code generation in many Java
Java (programming language)
Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...
and .NET
.NET Framework
The .NET Framework is a software framework that runs primarily on Microsoft Windows. It includes a large library and supports several programming languages which allows language interoperability...
SOAP frameworks (frameworks such as Apache Axis2
Apache Axis2
Apache Axis2 is a core engine for Web services. It is a complete re-design and re-write of the widely used Apache Axis SOAP stack. Implementations of Axis2 are available in Java and C....
, Apache CXF
Apache CXF
Apache CXF is an open-source, fully featured Web services framework. It originated as the combination of two open-source projects: Celtix developed by IONA Technologies and XFire developed by a team hosted at Codehaus. These two projects were combined by people working together at the Apache...
, and Spring being notable exceptions). Some industry organizations, such as the WS-I
Web Services Interoperability
The Web Services Interoperability Organization is an industry consortium chartered to promote interoperability amongst the stack of web services specifications. WS-I does not define standards for web services; rather, it creates guidelines and tests for interoperability...
, mandate both SOAP and WSDL in their definition of a Web service.
Web API
Web api
A web API is typically a defined set of HTTP request messages along with a definition of the structure of response messages, typically expressed in JSON or XML...
is a development in Web services (in a movement called Web 2.0
Web 2.0
The term Web 2.0 is associated with web applications that facilitate participatory information sharing, interoperability, user-centered design, and collaboration on the World Wide Web...
) where emphasis has been moving away from SOAP
SOAP
SOAP, originally defined as Simple Object Access Protocol, is a protocol specification for exchanging structured information in the implementation of Web Services in computer networks...
based services towards representational state transfer
Representational State Transfer
Representational state transfer is a style of software architecture for distributed hypermedia systems such as the World Wide Web. The term representational state transfer was introduced and defined in 2000 by Roy Fielding in his doctoral dissertation...
(REST) based communications. REST services do not require XML, SOAP, or WSDL
Web Services Description Language
The Web Services Description Language is an XML-based language that is used for describing the functionality offered by a Web service. A WSDL description of a web service provides a machine-readable description of how the service can be called, what parameters it expects and what data structures...
service-API definitions.
Web APIs allow the combination of multiple Web services into new applications known as mashup
Mashup (web application hybrid)
In Web development, a mashup is a Web page or application that uses and combines data, presentation or functionality from two or more sources to create new services...
s.
When used in the context of Web development
Web development
Web development is a broad term for the work involved in developing a web site for the Internet or an intranet . This can include web design, web content development, client liaison, client-side/server-side scripting, web server and network security configuration, and e-commerce development...
, Web API is typically a defined set of Hypertext Transfer Protocol (HTTP
Hypertext Transfer Protocol
The Hypertext Transfer Protocol is a networking protocol for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web....
) request messages along with a definition of the structure of response messages, usually expressed in an Extensible Markup Language (XML
XML
Extensible Markup Language is a set of rules for encoding documents in machine-readable form. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards....
) or JavaScript Object Notation (JSON
JSON
JSON , or JavaScript Object Notation, is a lightweight text-based open standard designed for human-readable data interchange. It is derived from the JavaScript scripting language for representing simple data structures and associative arrays, called objects...
) format.
When running composite Web services, each sub service can be considered autonomous. The user has no control over these services. Also the Web services themselves are not reliable; the service provider may remove, change or update their services without giving notice to users. The reliability and fault tolerance is not well supported; faults may happen during the execution. Exception handling in the context of Web services is still an open research issue, although this can still be handled by responding with an error object to the clients.
Styles of use
Web services are a set of tools that can be used in a number of ways. The three most common styles of use are RPCRemote procedure call
In computer science, a remote procedure call is an inter-process communication that allows a computer program to cause a subroutine or procedure to execute in another address space without the programmer explicitly coding the details for this remote interaction...
, SOA
Service-oriented architecture
In software engineering, a Service-Oriented Architecture is a set of principles and methodologies for designing and developing software in the form of interoperable services. These services are well-defined business functionalities that are built as software components that can be reused for...
and REST
Representational State Transfer
Representational state transfer is a style of software architecture for distributed hypermedia systems such as the World Wide Web. The term representational state transfer was introduced and defined in 2000 by Roy Fielding in his doctoral dissertation...
.
Remote procedure calls
RPC Web services present a distributed function (or method) call interface that is familiar to many developers. Typically, the basic unit of RPC Web services is the WSDL operation.
The first Web services tools were focused on RPC, and as a result this style is widely deployed and supported. However, it is sometimes criticized for not being loosely coupled
Loose coupling
In computing and systems design a loosely coupled system is one where each of its components has, or makes use of, little or no knowledge of the definitions of other separate components. The notion was introduced into organizational studies by Karl Weick...
, because it was often implemented by mapping services directly to language-specific functions or method calls. Many vendors felt this approach to be a dead end, and pushed for RPC to be disallowed in the WS-I Basic Profile
WS-I Basic Profile
The WS-I Basic Profile , a specification from the Web Services Interoperability industry consortium , provides interoperability guidance for core Web Services specifications such as SOAP, WSDL, and UDDI...
.
Other approaches with nearly the same functionality as RPC are: Object Management Group
Object Management Group
Object Management Group is a consortium, originally aimed at setting standards for distributed object-oriented systems, and is now focused on modeling and model-based standards.- Overview :...
's (OMG) Common Object Request Broker Architecture (CORBA
Common Object Request Broker Architecture
The Common Object Request Broker Architecture is a standard defined by the Object Management Group that enables software components written in multiple computer languages and running on multiple computers to work together .- Overview:CORBA enables separate pieces of software written in different...
), Open Software Foundation
Open Software Foundation
The Open Software Foundation was a not-for-profit organization founded in 1988 under the U.S. National Cooperative Research Act of 1984 to create an open standard for an implementation of the UNIX operating system.-History:...
's (OSF) DCE/RPC
DCE/RPC
DCE/RPC, short for "Distributed Computing Environment / Remote Procedure Calls", is the remote procedure call system developed for the Distributed Computing Environment...
, Microsoft
Microsoft
Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
's RPC (a part of DCOM
Distributed component object model
Distributed Component Object Model is a proprietary Microsoft technology for communication among software components distributed across networked computers. DCOM, which originally was called "Network OLE", extends Microsoft's COM, and provides the communication substrate under Microsoft's COM+...
) or .NET Remoting
.NET Remoting
.NET Remoting is a Microsoft application programming interface for interprocess communication released in 2002 with the 1.0 version of .NET Framework. It is one in a series of Microsoft technologies that began in 1990 with the first version of Object Linking and Embedding for 16-bit Windows...
and Sun Microsystems
Sun Microsystems
Sun Microsystems, Inc. was a company that sold :computers, computer components, :computer software, and :information technology services. Sun was founded on February 24, 1982...
's Java/Remote Method Invocation (RMI
Java remote method invocation
The Java Remote Method Invocation Application Programming Interface , or Java RMI, is a Java application programming interface that performs the object-oriented equivalent of remote procedure calls ....
).
Service-oriented architecture
Web services can also be used to implement an architecture according to service-oriented architecture (SOA) concepts, where the basic unit of communication is a message, rather than an operation. This is often referred to as "message-orientedMessage-oriented middleware
Message-oriented middleware is software or hardware infrastructure supporting sending and receiving messages between distributed systems. MOM allows application modules to be distributed over heterogeneous platforms and reduces the complexity of developing applications that span multiple...
" services.
SOA Web services are supported by most major software vendors and industry analysts. Unlike RPC Web services, loose coupling
Loose coupling
In computing and systems design a loosely coupled system is one where each of its components has, or makes use of, little or no knowledge of the definitions of other separate components. The notion was introduced into organizational studies by Karl Weick...
is more likely, because the focus is on the "contract" that WSDL provides, rather than the underlying implementation details.
Middleware analyst
Middleware analyst
Middleware analysts are computer software engineers with a specialization in products that connect two different computer systems together. These products can be open-source or proprietary...
s use enterprise service bus
Enterprise service bus
An enterprise service bus is a software architecture model used for designing and implementing the interaction and communication between mutually interacting software applications in Service Oriented Architecture...
es (ESBs) that combine message-oriented
Message-oriented middleware
Message-oriented middleware is software or hardware infrastructure supporting sending and receiving messages between distributed systems. MOM allows application modules to be distributed over heterogeneous platforms and reduces the complexity of developing applications that span multiple...
processing and Web services to create an event-driven SOA
Event-driven SOA
Event-driven SOA is a form of service-oriented architecture , combining the intelligence and proactiveness of event-driven architecture with the organizational capabilities found in service offerings...
. Examples of open-source ESB are Mule
Mule (software)
Mule is a lightweight enterprise service bus and integration framework. It can handle services and applications using disparate transport and messaging technologies...
and Open ESB
Open ESB
Open ESB is a Java based open source enterprise service bus. Open ESB can be used as a platform for both Enterprise Application Integration and SOA. Open ESB is built on open standards....
. An alternate approach is the Hub-and-Spoke model, which is server based. An example of this is Enterprise Message Service (EMS, an implementation of JMS).
Representational state transfer (REST)
REST attempts to describe architectures that use HTTP or similar protocols by constraining the interface to a set of well-known, standard operations (like GET, POST, PUT, DELETE for HTTP). Here, the focus is on interacting with statefulState (computer science)
In computer science and automata theory, a state is a unique configuration of information in a program or machine. It is a concept that occasionally extends into some forms of systems programming such as lexers and parsers....
resources, rather than messages or operations. Clean URLs are tightly associated with the REST concept.
An architecture based on REST (one that is 'RESTful') can use WSDL to describe SOAP messaging over HTTP, can be implemented as an abstraction purely on top of SOAP (e.g., WS-Transfer), or can be created without using SOAP at all.
WSDL version 2.0
Web Services Description Language
The Web Services Description Language is an XML-based language that is used for describing the functionality offered by a Web service. A WSDL description of a web service provides a machine-readable description of how the service can be called, what parameters it expects and what data structures...
offers support for binding to all the HTTP request methods (not only GET and POST as in version 1.1) so it enables a better implementation of RESTful web service
Representational State Transfer
Representational state transfer is a style of software architecture for distributed hypermedia systems such as the World Wide Web. The term representational state transfer was introduced and defined in 2000 by Roy Fielding in his doctoral dissertation...
s. However, support for this specification is still poor in software development kit
Software development kit
A software development kit is typically a set of software development tools that allows for the creation of applications for a certain software package, software framework, hardware platform, computer system, video game console, operating system, or similar platform.It may be something as simple...
s, which often offer tools only for WSDL 1.1.
Automated design methodologies
Automated tools can aid in the creation of a Web service. For services using WSDL it is possible to either automatically generate WSDL for existing classes (a bottom-up strategy) or to generate a class skeleton given existing WSDL (a top-down strategy).- A developer using a bottom up method writes implementing classes first (in some programming language), and then uses a WSDL generating tool to expose methods from these classes as a Web service. This is often the simpler approach.
- A developer using a top down method writes the WSDL document first and then uses a code generating tool to produce the class skeleton, to be completed as necessary. This way is generally considered more difficult but can produce cleaner designs
Criticisms
Critics of non-RESTful Web services often complain that they are too complex and based upon large software vendors or integrators, rather than typical open sourceOpen source
The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...
implementations. There are open source implementations like Apache Axis
Apache Axis
Apache Axis is an open source, XML based Web service framework. It consists of a Java and a C++ implementation of the SOAP server, and various utilities and APIs for generating and deploying Web service applications. Using Apache Axis, developers can create interoperable, distributed computing...
and Apache CXF
Apache CXF
Apache CXF is an open-source, fully featured Web services framework. It originated as the combination of two open-source projects: Celtix developed by IONA Technologies and XFire developed by a team hosted at Codehaus. These two projects were combined by people working together at the Apache...
.
One key concern of the REST Web service developers is that the SOAP WS toolkits make it easy to define new interfaces for remote interaction, often relying on introspection to extract the WDL, since a minor change on the server (even an upgrade of the SOAP stack) can result in different WSDL and a different service interface. The client-side classes that can be generated from WSDL and XSD descriptions of the service are often similarly tied to a particular version of the SOAP endpoint and can break, if the endpoint changes or the client-side SOAP stack is upgraded. Well-designed SOAP endpoints (with handwritten XSD and WSDL) do not suffer from this but there is still the problem that a custom interface for every service requires a custom client for every service.
There are also concerns about performance due to Web services' use of XML as a message format and SOAP/HTTP in enveloping and transport.
See also
- Amazon Web ServicesAmazon Web ServicesAmazon Web Services is a collection of remote computing services that together make up a cloud computing platform, offered over the Internet by Amazon.com...
- Business Intelligence 2.0Business Intelligence 2.0Business Intelligence 2.0 is a term that refers to new tools and software for business intelligence, beginning in the mid-2000s, that enable, among other things, dynamic querying of real-time corporate data by employees, and a more web- and browser-based approached to such data, as opposed to the...
(BI 2.0) - Devices Profile for Web ServicesDevices Profile for Web ServicesThe Devices Profile for Web Services defines a minimal set of implementation constraints to enable secure Web Service messaging, discovery, description, and eventing on resource-constrained devices....
- Enterprise Information IntegrationEnterprise Information IntegrationEnterprise Information Integration , is a process of information integration, using data abstraction to provide a unified interface for viewing all the data within an organization, and a single set of structures and naming conventions to represent this data; the goal of EII is to get a large set of...
(EII) - List of web service frameworks
- List of web service specifications
- Microsoft Connected Services Framework
- OAuthOAuthOAuth is an open standard for authorization. It allows users to share their private resources stored on one site with another site without having to hand out their credentials, typically username and password.OAuth allows users to hand out tokens instead of credentials to their data hosted by a...
- Service Implementation BeanService Implementation BeanA Service Implementation Bean , is a term used in Java Platform, Enterprise Edition, for a Java object implementing a web service. It can be either a POJO or a Stateless Session EJB. The Java interface of an SIB is called a Service Endpoint Interface .-External links:*...
- Service systemService systemA service system is a configuration of technology and organizational networks designed to deliver services that satisfy the needs, wants, or aspirations of customers.- Scope of the term :...
- Service-oriented architectureService-oriented architectureIn software engineering, a Service-Oriented Architecture is a set of principles and methodologies for designing and developing software in the form of interoperable services. These services are well-defined business functionalities that are built as software components that can be reused for...
(SOA) - SOAPjrSOAPjrSOAPjr is a protocol specification for exchanging structured information in the implementation of Web services in computer networks. It is a hybrid of SOAP and JSON-RPC .-Introduction:...
- Web Processing ServiceWeb Processing ServiceThe OGC Web Processing Service Interface Standard provides rules for standardizing how inputs and outputs for invoking geospatial processing services, such as polygon overlay, as a Web service. The WPS standard defines how a client can request the execution of a process, and how the output from...
- Web serverWeb serverWeb server can refer to either the hardware or the software that helps to deliver content that can be accessed through the Internet....
- Web Services DiscoveryWeb Services DiscoveryWeb services provide access to software systems over the Internet using standard protocols. In a minimalistic scenario there exists at least a Web service provider that publishes some service such as a weather service and a Web service consumer that uses this service...
External links
- Messaging Design Pattern and a distributed component/service model
- W3C Web Services Activity home page
- Web Services Architecture (W3C Working Group Note)
- Where to find Web Services on the Web: Investigating Web Services on the World Wide Web (2008)
The W3C defines a "Web service" as "a software system designed to support interoperable
Interoperability
Interoperability is a property referring to the ability of diverse systems and organizations to work together . The term is often used in a technical systems engineering sense, or alternatively in a broad sense, taking into account social, political, and organizational factors that impact system to...
machine-to-machine interaction over a network
Computer network
A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....
". It has an interface described in a machine-processable format (specifically Web Services Description Language, known by the acronym WSDL
Web Services Description Language
The Web Services Description Language is an XML-based language that is used for describing the functionality offered by a Web service. A WSDL description of a web service provides a machine-readable description of how the service can be called, what parameters it expects and what data structures...
). Other systems interact with the Web service in a manner prescribed by its description using SOAP
SOAP
SOAP, originally defined as Simple Object Access Protocol, is a protocol specification for exchanging structured information in the implementation of Web Services in computer networks...
messages, typically conveyed using HTTP with an XML serialization in conjunction with other Web-related standards."
The W3C also states, "We can identify two major classes of Web services, REST
Representational State Transfer
Representational state transfer is a style of software architecture for distributed hypermedia systems such as the World Wide Web. The term representational state transfer was introduced and defined in 2000 by Roy Fielding in his doctoral dissertation...
-compliant Web services, in which the primary purpose of the service is to manipulate XML representations of Web resources using a uniform set of "stateless" operations; and arbitrary Web services, in which the service may expose an arbitrary set of operations."
Big Web services
"Big Web services" use Extensible Markup LanguageXML
Extensible Markup Language is a set of rules for encoding documents in machine-readable form. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards....
(XML) messages that follow the SOAP
SOAP
SOAP, originally defined as Simple Object Access Protocol, is a protocol specification for exchanging structured information in the implementation of Web Services in computer networks...
standard and have been popular with traditional enterprises. In such systems, there is often a machine-readable description of the operations offered by the service written in the Web Services Description Language
Web Services Description Language
The Web Services Description Language is an XML-based language that is used for describing the functionality offered by a Web service. A WSDL description of a web service provides a machine-readable description of how the service can be called, what parameters it expects and what data structures...
(WSDL). The latter is not a requirement of a SOAP endpoint, but it is a prerequisite for automated client-side
Client-side
Client-side refers to operations that are performed by the client in a client–server relationship in a computer network.Typically, a client is a computer application, such as a web browser, that runs on a user's local computer or workstation and connects to a server as necessary...
code generation in many Java
Java (programming language)
Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...
and .NET
.NET Framework
The .NET Framework is a software framework that runs primarily on Microsoft Windows. It includes a large library and supports several programming languages which allows language interoperability...
SOAP frameworks (frameworks such as Apache Axis2
Apache Axis2
Apache Axis2 is a core engine for Web services. It is a complete re-design and re-write of the widely used Apache Axis SOAP stack. Implementations of Axis2 are available in Java and C....
, Apache CXF
Apache CXF
Apache CXF is an open-source, fully featured Web services framework. It originated as the combination of two open-source projects: Celtix developed by IONA Technologies and XFire developed by a team hosted at Codehaus. These two projects were combined by people working together at the Apache...
, and Spring being notable exceptions). Some industry organizations, such as the WS-I
Web Services Interoperability
The Web Services Interoperability Organization is an industry consortium chartered to promote interoperability amongst the stack of web services specifications. WS-I does not define standards for web services; rather, it creates guidelines and tests for interoperability...
, mandate both SOAP and WSDL in their definition of a Web service.
Web API
Web api
A web API is typically a defined set of HTTP request messages along with a definition of the structure of response messages, typically expressed in JSON or XML...
is a development in Web services (in a movement called Web 2.0
Web 2.0
The term Web 2.0 is associated with web applications that facilitate participatory information sharing, interoperability, user-centered design, and collaboration on the World Wide Web...
) where emphasis has been moving away from SOAP
SOAP
SOAP, originally defined as Simple Object Access Protocol, is a protocol specification for exchanging structured information in the implementation of Web Services in computer networks...
based services towards representational state transfer
Representational State Transfer
Representational state transfer is a style of software architecture for distributed hypermedia systems such as the World Wide Web. The term representational state transfer was introduced and defined in 2000 by Roy Fielding in his doctoral dissertation...
(REST) based communications. REST services do not require XML, SOAP, or WSDL
Web Services Description Language
The Web Services Description Language is an XML-based language that is used for describing the functionality offered by a Web service. A WSDL description of a web service provides a machine-readable description of how the service can be called, what parameters it expects and what data structures...
service-API definitions.
Web APIs allow the combination of multiple Web services into new applications known as mashup
Mashup (web application hybrid)
In Web development, a mashup is a Web page or application that uses and combines data, presentation or functionality from two or more sources to create new services...
s.
When used in the context of Web development
Web development
Web development is a broad term for the work involved in developing a web site for the Internet or an intranet . This can include web design, web content development, client liaison, client-side/server-side scripting, web server and network security configuration, and e-commerce development...
, Web API is typically a defined set of Hypertext Transfer Protocol (HTTP
Hypertext Transfer Protocol
The Hypertext Transfer Protocol is a networking protocol for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web....
) request messages along with a definition of the structure of response messages, usually expressed in an Extensible Markup Language (XML
XML
Extensible Markup Language is a set of rules for encoding documents in machine-readable form. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards....
) or JavaScript Object Notation (JSON
JSON
JSON , or JavaScript Object Notation, is a lightweight text-based open standard designed for human-readable data interchange. It is derived from the JavaScript scripting language for representing simple data structures and associative arrays, called objects...
) format.
When running composite Web services, each sub service can be considered autonomous. The user has no control over these services. Also the Web services themselves are not reliable; the service provider may remove, change or update their services without giving notice to users. The reliability and fault tolerance is not well supported; faults may happen during the execution. Exception handling in the context of Web services is still an open research issue, although this can still be handled by responding with an error object to the clients.
Styles of use
Web services are a set of tools that can be used in a number of ways. The three most common styles of use are RPCRemote procedure call
In computer science, a remote procedure call is an inter-process communication that allows a computer program to cause a subroutine or procedure to execute in another address space without the programmer explicitly coding the details for this remote interaction...
, SOA
Service-oriented architecture
In software engineering, a Service-Oriented Architecture is a set of principles and methodologies for designing and developing software in the form of interoperable services. These services are well-defined business functionalities that are built as software components that can be reused for...
and REST
Representational State Transfer
Representational state transfer is a style of software architecture for distributed hypermedia systems such as the World Wide Web. The term representational state transfer was introduced and defined in 2000 by Roy Fielding in his doctoral dissertation...
.
Remote procedure calls
RPC Web services present a distributed function (or method) call interface that is familiar to many developers. Typically, the basic unit of RPC Web services is the WSDL operation.
The first Web services tools were focused on RPC, and as a result this style is widely deployed and supported. However, it is sometimes criticized for not being loosely coupled
Loose coupling
In computing and systems design a loosely coupled system is one where each of its components has, or makes use of, little or no knowledge of the definitions of other separate components. The notion was introduced into organizational studies by Karl Weick...
, because it was often implemented by mapping services directly to language-specific functions or method calls. Many vendors felt this approach to be a dead end, and pushed for RPC to be disallowed in the WS-I Basic Profile
WS-I Basic Profile
The WS-I Basic Profile , a specification from the Web Services Interoperability industry consortium , provides interoperability guidance for core Web Services specifications such as SOAP, WSDL, and UDDI...
.
Other approaches with nearly the same functionality as RPC are: Object Management Group
Object Management Group
Object Management Group is a consortium, originally aimed at setting standards for distributed object-oriented systems, and is now focused on modeling and model-based standards.- Overview :...
's (OMG) Common Object Request Broker Architecture (CORBA
Common Object Request Broker Architecture
The Common Object Request Broker Architecture is a standard defined by the Object Management Group that enables software components written in multiple computer languages and running on multiple computers to work together .- Overview:CORBA enables separate pieces of software written in different...
), Open Software Foundation
Open Software Foundation
The Open Software Foundation was a not-for-profit organization founded in 1988 under the U.S. National Cooperative Research Act of 1984 to create an open standard for an implementation of the UNIX operating system.-History:...
's (OSF) DCE/RPC
DCE/RPC
DCE/RPC, short for "Distributed Computing Environment / Remote Procedure Calls", is the remote procedure call system developed for the Distributed Computing Environment...
, Microsoft
Microsoft
Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
's RPC (a part of DCOM
Distributed component object model
Distributed Component Object Model is a proprietary Microsoft technology for communication among software components distributed across networked computers. DCOM, which originally was called "Network OLE", extends Microsoft's COM, and provides the communication substrate under Microsoft's COM+...
) or .NET Remoting
.NET Remoting
.NET Remoting is a Microsoft application programming interface for interprocess communication released in 2002 with the 1.0 version of .NET Framework. It is one in a series of Microsoft technologies that began in 1990 with the first version of Object Linking and Embedding for 16-bit Windows...
and Sun Microsystems
Sun Microsystems
Sun Microsystems, Inc. was a company that sold :computers, computer components, :computer software, and :information technology services. Sun was founded on February 24, 1982...
's Java/Remote Method Invocation (RMI
Java remote method invocation
The Java Remote Method Invocation Application Programming Interface , or Java RMI, is a Java application programming interface that performs the object-oriented equivalent of remote procedure calls ....
).
Service-oriented architecture
Web services can also be used to implement an architecture according to service-oriented architecture (SOA) concepts, where the basic unit of communication is a message, rather than an operation. This is often referred to as "message-orientedMessage-oriented middleware
Message-oriented middleware is software or hardware infrastructure supporting sending and receiving messages between distributed systems. MOM allows application modules to be distributed over heterogeneous platforms and reduces the complexity of developing applications that span multiple...
" services.
SOA Web services are supported by most major software vendors and industry analysts. Unlike RPC Web services, loose coupling
Loose coupling
In computing and systems design a loosely coupled system is one where each of its components has, or makes use of, little or no knowledge of the definitions of other separate components. The notion was introduced into organizational studies by Karl Weick...
is more likely, because the focus is on the "contract" that WSDL provides, rather than the underlying implementation details.
Middleware analyst
Middleware analyst
Middleware analysts are computer software engineers with a specialization in products that connect two different computer systems together. These products can be open-source or proprietary...
s use enterprise service bus
Enterprise service bus
An enterprise service bus is a software architecture model used for designing and implementing the interaction and communication between mutually interacting software applications in Service Oriented Architecture...
es (ESBs) that combine message-oriented
Message-oriented middleware
Message-oriented middleware is software or hardware infrastructure supporting sending and receiving messages between distributed systems. MOM allows application modules to be distributed over heterogeneous platforms and reduces the complexity of developing applications that span multiple...
processing and Web services to create an event-driven SOA
Event-driven SOA
Event-driven SOA is a form of service-oriented architecture , combining the intelligence and proactiveness of event-driven architecture with the organizational capabilities found in service offerings...
. Examples of open-source ESB are Mule
Mule (software)
Mule is a lightweight enterprise service bus and integration framework. It can handle services and applications using disparate transport and messaging technologies...
and Open ESB
Open ESB
Open ESB is a Java based open source enterprise service bus. Open ESB can be used as a platform for both Enterprise Application Integration and SOA. Open ESB is built on open standards....
. An alternate approach is the Hub-and-Spoke model, which is server based. An example of this is Enterprise Message Service (EMS, an implementation of JMS).
Representational state transfer (REST)
REST attempts to describe architectures that use HTTP or similar protocols by constraining the interface to a set of well-known, standard operations (like GET, POST, PUT, DELETE for HTTP). Here, the focus is on interacting with statefulState (computer science)
In computer science and automata theory, a state is a unique configuration of information in a program or machine. It is a concept that occasionally extends into some forms of systems programming such as lexers and parsers....
resources, rather than messages or operations. Clean URLs are tightly associated with the REST concept.
An architecture based on REST (one that is 'RESTful') can use WSDL to describe SOAP messaging over HTTP, can be implemented as an abstraction purely on top of SOAP (e.g., WS-Transfer), or can be created without using SOAP at all.
WSDL version 2.0
Web Services Description Language
The Web Services Description Language is an XML-based language that is used for describing the functionality offered by a Web service. A WSDL description of a web service provides a machine-readable description of how the service can be called, what parameters it expects and what data structures...
offers support for binding to all the HTTP request methods (not only GET and POST as in version 1.1) so it enables a better implementation of RESTful web service
Representational State Transfer
Representational state transfer is a style of software architecture for distributed hypermedia systems such as the World Wide Web. The term representational state transfer was introduced and defined in 2000 by Roy Fielding in his doctoral dissertation...
s. However, support for this specification is still poor in software development kit
Software development kit
A software development kit is typically a set of software development tools that allows for the creation of applications for a certain software package, software framework, hardware platform, computer system, video game console, operating system, or similar platform.It may be something as simple...
s, which often offer tools only for WSDL 1.1.
Automated design methodologies
Automated tools can aid in the creation of a Web service. For services using WSDL it is possible to either automatically generate WSDL for existing classes (a bottom-up strategy) or to generate a class skeleton given existing WSDL (a top-down strategy).- A developer using a bottom up method writes implementing classes first (in some programming language), and then uses a WSDL generating tool to expose methods from these classes as a Web service. This is often the simpler approach.
- A developer using a top down method writes the WSDL document first and then uses a code generating tool to produce the class skeleton, to be completed as necessary. This way is generally considered more difficult but can produce cleaner designs
Criticisms
Critics of non-RESTful Web services often complain that they are too complex and based upon large software vendors or integrators, rather than typical open sourceOpen source
The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...
implementations. There are open source implementations like Apache Axis
Apache Axis
Apache Axis is an open source, XML based Web service framework. It consists of a Java and a C++ implementation of the SOAP server, and various utilities and APIs for generating and deploying Web service applications. Using Apache Axis, developers can create interoperable, distributed computing...
and Apache CXF
Apache CXF
Apache CXF is an open-source, fully featured Web services framework. It originated as the combination of two open-source projects: Celtix developed by IONA Technologies and XFire developed by a team hosted at Codehaus. These two projects were combined by people working together at the Apache...
.
One key concern of the REST Web service developers is that the SOAP WS toolkits make it easy to define new interfaces for remote interaction, often relying on introspection to extract the WDL, since a minor change on the server (even an upgrade of the SOAP stack) can result in different WSDL and a different service interface. The client-side classes that can be generated from WSDL and XSD descriptions of the service are often similarly tied to a particular version of the SOAP endpoint and can break, if the endpoint changes or the client-side SOAP stack is upgraded. Well-designed SOAP endpoints (with handwritten XSD and WSDL) do not suffer from this but there is still the problem that a custom interface for every service requires a custom client for every service.
There are also concerns about performance due to Web services' use of XML as a message format and SOAP/HTTP in enveloping and transport.
See also
- Amazon Web ServicesAmazon Web ServicesAmazon Web Services is a collection of remote computing services that together make up a cloud computing platform, offered over the Internet by Amazon.com...
- Business Intelligence 2.0Business Intelligence 2.0Business Intelligence 2.0 is a term that refers to new tools and software for business intelligence, beginning in the mid-2000s, that enable, among other things, dynamic querying of real-time corporate data by employees, and a more web- and browser-based approached to such data, as opposed to the...
(BI 2.0) - Devices Profile for Web ServicesDevices Profile for Web ServicesThe Devices Profile for Web Services defines a minimal set of implementation constraints to enable secure Web Service messaging, discovery, description, and eventing on resource-constrained devices....
- Enterprise Information IntegrationEnterprise Information IntegrationEnterprise Information Integration , is a process of information integration, using data abstraction to provide a unified interface for viewing all the data within an organization, and a single set of structures and naming conventions to represent this data; the goal of EII is to get a large set of...
(EII) - List of web service frameworks
- List of web service specifications
- Microsoft Connected Services Framework
- OAuthOAuthOAuth is an open standard for authorization. It allows users to share their private resources stored on one site with another site without having to hand out their credentials, typically username and password.OAuth allows users to hand out tokens instead of credentials to their data hosted by a...
- Service Implementation BeanService Implementation BeanA Service Implementation Bean , is a term used in Java Platform, Enterprise Edition, for a Java object implementing a web service. It can be either a POJO or a Stateless Session EJB. The Java interface of an SIB is called a Service Endpoint Interface .-External links:*...
- Service systemService systemA service system is a configuration of technology and organizational networks designed to deliver services that satisfy the needs, wants, or aspirations of customers.- Scope of the term :...
- Service-oriented architectureService-oriented architectureIn software engineering, a Service-Oriented Architecture is a set of principles and methodologies for designing and developing software in the form of interoperable services. These services are well-defined business functionalities that are built as software components that can be reused for...
(SOA) - SOAPjrSOAPjrSOAPjr is a protocol specification for exchanging structured information in the implementation of Web services in computer networks. It is a hybrid of SOAP and JSON-RPC .-Introduction:...
- Web Processing ServiceWeb Processing ServiceThe OGC Web Processing Service Interface Standard provides rules for standardizing how inputs and outputs for invoking geospatial processing services, such as polygon overlay, as a Web service. The WPS standard defines how a client can request the execution of a process, and how the output from...
- Web serverWeb serverWeb server can refer to either the hardware or the software that helps to deliver content that can be accessed through the Internet....
- Web Services DiscoveryWeb Services DiscoveryWeb services provide access to software systems over the Internet using standard protocols. In a minimalistic scenario there exists at least a Web service provider that publishes some service such as a weather service and a Web service consumer that uses this service...
External links
- Messaging Design Pattern and a distributed component/service model
- W3C Web Services Activity home page
- Web Services Architecture (W3C Working Group Note)
- Where to find Web Services on the Web: Investigating Web Services on the World Wide Web (2008)