Service Oriented Architecture Library (SOALIB) is used to distribute reusable Service Oriented Architecture (SOA) software in a manner similar to other computing libraries. SOA consists of loosely coupled interoperable services which use messaging based on both Simple Object Access Protocol (SOAP) and 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). A library in computing is a set of compiled modules which are tested and ready for reuse. A similar concept is used for SOA, in that whatever technology is used to develop the service can also be distributed in library form. A Java-based SOA library may be distributed in Web ARchive (WAR) or Enterprise Archive

EAR (file format)

EAR is a file format used by Java EE for packaging one or more modules into a single archive so that the deployment of the various modules onto an application server happens simultaneously and coherently...

 (EAR) file formats. C

C (programming language)

C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....

, C++

C++

C++ is a statically typed, free-form, multi-paradigm, compiled, general-purpose programming language. It is regarded as an intermediate-level language, as it comprises a combination of both high-level and low-level language features. It was developed by Bjarne Stroustrup starting in 1979 at Bell...

, 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...

 applications may be distributed as a shared object (in Unix

Unix

Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...

 and Linux

Linux

Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...

), a Dynamic Link Library

Dynamic-link library

Dynamic-link library , or DLL, is Microsoft's implementation of the shared library concept in the Microsoft Windows and OS/2 operating systems...

 (in Windows), or as an executable

Executable

In computing, an executable file causes a computer "to perform indicated tasks according to encoded instructions," as opposed to a data file that must be parsed by a program to be meaningful. These instructions are traditionally machine code instructions for a physical CPU...

 file.

History

Service Oriented Architecture is usually tied to the redesign of an entire software system and determines how to decompose the single software unit into loosely coupled components, in which each loosely coupled components acts as interoperable services. Such a task is enormous and may take significant amount of time, while on the atomic level (where atom is defined as a single loosely-coupled service that is self-contained), most services are reusable regardless of the application. As an example, all matter is built with atoms, yet all material things are different. At the atomic level, however, they appear uniform. Similarly, all software can be built on loosely-coupled services which serve as the "atoms" of the redesign process. Because loose coupling is difficult to determine, the opposite is not true. That means it is easier to build a complete software system by using available loosely-coupled services.

By building Service Oriented Architecture Libraries, each of which are loosely-coupled services, complex applications can be developed by making use of these services. Because new applications depend on all loosely-coupled services, as long as we stick to loose coupling, the final application is also loosely-coupled. While it is true that the final application depends on many hierarchical loosely-coupled systems, it remains loosely-coupled because all the hierarchy is based on atomic services.

Objectives

Building SOA requires the loose coupling of services as a starting point. They are termed as atomic services. The first step is to determine the atomic services. Then build these atomic services for reuse. A large number of such atomic services could be created, upon which composite services will be built. Composite service are services that are built only upon atomic services.

Steps

• Identify, build, and test loosely coupled atomic services.
• Identify, build, and test loosely coupled composite services, where each composite services is made up of atomic services only.
• Build integrated services, where each of the integrated services are made up of composite and atomic services.
• Build complex software system via the reuse of atomic, composite, and integrated services. This complex system remains loosely-coupled.

Platform independence

Consideration for cross platform

Cross-platform

In computing, cross-platform, or multi-platform, is an attribute conferred to computer software or computing methods and concepts that are implemented and inter-operate on multiple computer platforms...

 is important. Presently, there are many ways to make the services host platform to be platform independent. Examples are building services in Java, where JVM is available for the host in which the server will run as a service. Alternatives are building applications with full compliance to ANSI

Ansi

Ansi is a village in Kaarma Parish, Saare County, on the island of Saaremaa, Estonia....

 C/C++ so that none of the components of the code is reliant upon third party libraries. Typically, this means building the C/C++ applications using GNU

GNU

GNU is a Unix-like computer operating system developed by the GNU project, ultimately aiming to be a "complete Unix-compatible software system"...

 tools and GNU C compilers because GNU compilers are ported to most operating systems and platforms. Another alternative is to use C# .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...

 as the language of the web service where the Common Language Runtime

Common Language Runtime

The Common Language Runtime is the virtual machine component of Microsoft's .NET framework and is responsible for managing the execution of .NET programs. In a process known as just-in-time compilation, the CLR compiles the intermediate language code known as CIL into the machine instructions...

  is ported to the target operating system and platform. Many other options are available, but the most common approaches to the platform independence has already been mentioned.

Steps

• Full platform independence to the extent possible.
• Automatic tests on each platforms.

Multi-vendor database

The scope of the library is limited if it does not have support for databases. Composite and integration services should be built to take advantage of loosely-coupled atomic services which operate on databases. Once the support for database access is added, a metadata

Metadata

The term metadata is an ambiguous term which is used for two fundamentally different concepts . Although the expression "data about data" is often used, it does not apply to both in the same way. Structural metadata, the design and specification of data structures, cannot be about data, because at...

 layer should be added to map the various kinds of data format in the database into a uniform set of data types which will have equal meaning to all databases. This is the difficult part, but at this time, JDBC

Java Database Connectivity

Java DataBase Connectivity, commonly referred to as JDBC, is an API for the Java programming language that defines how a client may access a database. It provides methods for querying and updating data in a database. JDBC is oriented towards relational databases...

, ODBC

Open Database Connectivity

In computing, ODBC is a standard C interface for accessing database management systems . The designers of ODBC aimed to make it independent of database systems and operating systems...

, ADO

ActiveX Data Objects

Microsoft's ActiveX Data Objects is a set of Component Object Model objects for accessing data sources. A part of MDAC, it provides a middleware layer between programming languages and OLE DB...

 and other standards database drivers already do part of the task. Each database may store data in different formats. Some data may be encrypted, some may be stored in little endian Endianness

Endianness

In computing, the term endian or endianness refers to the ordering of individually addressable sub-components within the representation of a larger data item as stored in external memory . Each sub-component in the representation has a unique degree of significance, like the place value of digits...

, or others in big endian, and so on. Therefore, data must be transformed at some point by the services and they have to be done at runtime due to the changing nature of data. All databases are different, therefore, no single API can take advantage of all the features of all databases. Therefore, services should use database specific features as well.

Steps

• Full support for all major databases - mobile, PC, and server-based.
• Creation of a metadata layer for uniform data access.
• All database access through the service libraries.
• Automatic runtime data transformation.
• Support internal database specific features.

Data synchronization

Once multi-vendor databases are supported, services can be added so that each database may synchronize with any other database. This will now become possible as all data is now passed through a data layer and data is represented in some intermediate form. The intermediate form may be any native form and does not have to be standards-based. Usually, the native form should be portable, that means, representing it in 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....

 may be the best approach. Because data sizes tend to be large, incremental change detection should also be added.

Steps

• Any-to-any synchronization.
• Change capture engine.
• Uni- and bi-directional data synchronization.
• Custom mapping with referential integrity.
• Heterogeneous synchronization.

Security

All libraries must be secure. If the libraries have SOA implementation as web services, then it should have WS-Security

WS-Security

WS-Security is a flexible and feature-rich extension to SOAP to apply security to web services. It is a member of the WS-* family of web service specifications and was published by OASIS....

, WS-Policy

WS-Policy

WS-Policy is a specification that allows web services to use XML to advertise their policies and for web service consumers to specify their policy requirements.WS-Policy is a W3C recommendation as of September 2007....

 and other WS-type standards compliance. If based on REST or other protocols, then it should follow the respective standards. All libraries must at least support SSL

Transport Layer Security

Transport Layer Security and its predecessor, Secure Sockets Layer , are cryptographic protocols that provide communication security over the Internet...

.

Steps

• Support all major standards-based security architectures.
• Secure Socket Layer support.
• Option for encrypted storage on the server.

Interoperability

Interoperability is one of the most important reasons why SOA has been so important. A SOA library must also include the required API that could be used for rapid platform specific development.

Steps

• Support all major programming languages: 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...
  
  , Java ME, C
  C (programming language)
  C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
  
  , C++
  C++
  C++ is a statically typed, free-form, multi-paradigm, compiled, general-purpose programming language. It is regarded as an intermediate-level language, as it comprises a combination of both high-level and low-level language features. It was developed by Bjarne Stroustrup starting in 1979 at Bell...
  
  , C#.NET, VB.NET.
  Visual Basic .NET
  Visual Basic .NET , is an object-oriented computer programming language that can be viewed as an evolution of the classic Visual Basic , which is implemented on the .NET Framework...
  
  , PHP
• Supplied with all needed client APIs.
• All APIs must be tested against the binding SOA services.

Building applications atom by atom

An atomic service is a loosely-coupled service which is independent of any assumptions, absolutely predictable and have no other dependencies on services or other atomic services. As an example, a disk file operation may be considered as an atomic service in which the only operations performed by the service are read, write, delete, or append file operations. Because the only information the disk file would need is the full path to the file and possibly some access parameters (like username and password), there would be no other dependencies. If a composite service is designed based on atomic services, it is still loosely coupled, but not an atomic service. Each integrated service can then be built together to make a larger SOA application. By building layer by layer, a large SOA application may be created which will remain loosely-coupled.

General guidelines

To keep the integrated services loosely-coupled would require all the services to be built on atomic and composite services. As soon as the integrated service uses another service that is somewhat tightly-coupled, the entire service application becomes tightly-coupled. This is analogous to atomic structures becoming "charged" if there is just one electron missing. For this reason, when using third party services, the designer must ensure that the service remains loosely-coupled.

• If the service is reliant on third party services, those services must also be loosely-coupled.
• If third part offers atomic services, then composite services may be built by mixing Service Oriented Architecture Libraries as well as third party atomic services.
• If any of the services is deemed to be tightly-coupled, which may become necessary when there is an industrial appliance involved (e.g., Robotic Arms, Consumer Appliances, etc.), this should be the final service and no service should be derived from them. If other services are built on tightly-coupled services, the derived services are tightly-coupled as well. These derived services may be used in specialized applications where tight coupling is required (e.g., in precision machines).

The following is the hierarchy in which all service oriented applications should be designed.

Hierarchy

Ideally, the following should be the SOA application design approach:

• Integrated Services - based upon composite and atomic services
  • Composite Services - based only upon atomic services
    • Atomic Services - no dependency, this service is the atom

Structures to avoid

In some cases, loose coupling may not be possible due to reliance on hardware, mechanical systems, or specialized instruments. For example, if there is a service built to move a robotic arm, monitor industrial generators, or emergency hospital equipment. Then, tightly-coupled services are required. Tightly-coupled services should be the top in the hierarchy such that no other service may reuse tightly-coupled services, if possible. If there are derived services based on tightly-coupled services, then all derived services also become tightly-coupled. Such a system, if designed, should be limited to the scope of the purpose of the application.

External links

• Web Services Specification Up to date information about Web Services Specifications
• Representational State Transfer Architectural Styles and the Design of Network-based Software Architectures, PhD Dessertation, Dr. Roy Thomas Fielding