Data Distribution Service
Encyclopedia
Data distribution service for real-time systems (DDS) is a specification of a publish/subscribe
middleware
for distributed systems created by the Object Management Group
(OMG) in response to the need to standardize a data-centric
publish-subscribe programming model for distributed systems.
and the French Thales Group
teamed up to create the DDS specification in and which was subsequently approved by the Object Management Group
resulting in Version 1.0 in 2003.
Version History
The DDS specification describes two levels of interfaces:
that simplifies complex network programming
. It implements a publish/subscribe
model for sending and receiving data, events, and commands among the node
s. Nodes that are producing information (publishers) create "topics" (e.g., temperature, location, pressure) and publish "samples." DDS takes care of delivering the sample to all subscribers that declare an interest in that topic.
DDS handles all the transfer chores: message addressing, data marshalling and demarshalling
(so subscribers can be on different platforms than the publisher), delivery, flow control, retries, etc. Any node can be a publisher, subscriber, or both simultaneously.
The DDS publish-subscribe model virtually eliminates complex network programming for distributed applications.
DDS supports mechanisms that go beyond the basic publish-subscribe model. The key benefit is that applications that use DDS for their communications are entirely decoupled. Very little design time has to be spent on how to handle their mutual interactions. In particular, the applications never need information about the other participating applications, including their existence or locations. DDS automatically handles all aspects of message delivery, without requiring any intervention from the user applications, including:
This is made possible by the fact that DDS allows the user to specify Quality of Service
(QoS) parameters as a way to configure automatic-discovery mechanisms and specify the behavior used when sending and receiving messages. The mechanisms are configured up-front and require no further effort on the user's part. By exchanging messages in a completely anonymous manner, DDS greatly simplifies distributed application design and encourages modular, well-structured programs.
DDS also automatically handles hot-swapping redundant publishers if the primary fails. Subscribers always get the sample with the highest priority whose data is still valid (that is, whose publisher-specified validity period has not expired). It automatically switches back to the primary when it recovers, too. DDS is available from different vendors with Ada
, C
, C++
, C#, and Java
API
s.
Space Software Italia developed a JAVA DDS version for applications based on Fixed and Mobile Cooperating Multi-Agents (Swarm Systems)
Publish/subscribe
Publish–subscribe is a messaging pattern where senders of messages, called publishers, do not program the messages to be sent directly to specific receivers, called subscribers. Published messages are characterized into classes, without knowledge of what, if any, subscribers there may be...
middleware
Middleware
Middleware is computer software that connects software components or people and their applications. The software consists of a set of services that allows multiple processes running on one or more machines to interact...
for distributed systems created by the 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 :...
(OMG) in response to the need to standardize a data-centric
Database-centric architecture
Database-centric architecture or data-centric architecture has several distinct meanings, generally relating to software architectures in which databases play a crucial role. Often this description is meant to contrast the design to an alternative approach...
publish-subscribe programming model for distributed systems.
History
A few proprietary DDS solutions had been available for several years. Starting in 2001, two major DDS vendors, the American group Real-Time InnovationsReal-Time Innovations
Real Time Innovations, Inc. is a computer networking software company headquartered in Sunnyvale, California specializing in publish/subscribe middleware. The company's major competitors are PrismTech, 29West, and TIBCO Software.- History :...
and the French Thales Group
Thales Group
The Thales Group is a French electronics company delivering information systems and services for the aerospace, defense, transportation and security markets...
teamed up to create the DDS specification in and which was subsequently approved by the 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 :...
resulting in Version 1.0 in 2003.
Version History
- DDS 1.3 — Working version, OMG members only.
- DDS 1.2 (January 1, 2007)
- DDS 1.1 (December 4, 2005)
- DDS 1.0 (June 1, 2003)
The DDS specification describes two levels of interfaces:
- A lower DCPS (Data-centric publish-subscribe) level that is targeted towards the efficient delivery of the proper information to the proper recipients.
- An optional higher DLRL (data local reconstruction layer) level, which allows for a simple integration of DDS into the application layerApplication layerThe Internet protocol suite and the Open Systems Interconnection model of computer networking each specify a group of protocols and methods identified by the name application layer....
.
DDS entities
- DomainParticipantFactory: A singletonSingleton patternIn software engineering, the singleton pattern is a design pattern used to implement the mathematical concept of a singleton, by restricting the instantiation of a class to one object. This is useful when exactly one object is needed to coordinate actions across the system...
factory that is the main entry point to DDS.
- DomainParticipant: Entry point for the communication in a specific domain; it represents the participation of an application in one DDS Domain. Furthermore, it acts as a factory for the creation of DDS Publishers, Subscribers, Topics, MultiTopics and ContentFilteredTopics.
- TopicDescription: Abstract base class for Topic, ContentFilteredTopic and MultiTopic.
- Topic: A specialization of TopicDescription that is the most basic description of the data to be published and subscribed.
- ContentFilteredTopic: A specialized TopicDescription like the Topic that additionally allows content-based subscriptions.
- MultiTopic: A specialization of TopicDescription like the Topic that additionally allows subscriptions to combine/filter/rearrange data coming from several topics.
- Publisher: A Publisher is the object responsible for the actual dissemination of publications.
- DataWriter: Allows the application to set the value of the data to be published under a given Topic.
- Subscriber: A Subscriber is the object responsible for the actual reception of the data resulting from its subscriptions.
- DataReader: A DataReader allows the application to declare the data it wishes to receive (by making a subscription using a Topic, ContentFilteredTopic or MultiTopic) and to access the data received by the attached Subscriber.
DDS model
DDS is networking middlewareMiddleware
Middleware is computer software that connects software components or people and their applications. The software consists of a set of services that allows multiple processes running on one or more machines to interact...
that simplifies complex network programming
Computer network programming
In computing, network programming, essentially identical to socket programming or client–server programming, involves writing computer programs that communicate with other programs across a computer network. The program or process initiating the communication is called a client process, and the...
. It implements a publish/subscribe
Publish/subscribe
Publish–subscribe is a messaging pattern where senders of messages, called publishers, do not program the messages to be sent directly to specific receivers, called subscribers. Published messages are characterized into classes, without knowledge of what, if any, subscribers there may be...
model for sending and receiving data, events, and commands among the node
Node (networking)
In communication networks, a node is a connection point, either a redistribution point or a communication endpoint . The definition of a node depends on the network and protocol layer referred to...
s. Nodes that are producing information (publishers) create "topics" (e.g., temperature, location, pressure) and publish "samples." DDS takes care of delivering the sample to all subscribers that declare an interest in that topic.
DDS handles all the transfer chores: message addressing, data marshalling and demarshalling
Serialization
In computer science, in the context of data storage and transmission, serialization is the process of converting a data structure or object state into a format that can be stored and "resurrected" later in the same or another computer environment...
(so subscribers can be on different platforms than the publisher), delivery, flow control, retries, etc. Any node can be a publisher, subscriber, or both simultaneously.
The DDS publish-subscribe model virtually eliminates complex network programming for distributed applications.
DDS supports mechanisms that go beyond the basic publish-subscribe model. The key benefit is that applications that use DDS for their communications are entirely decoupled. Very little design time has to be spent on how to handle their mutual interactions. In particular, the applications never need information about the other participating applications, including their existence or locations. DDS automatically handles all aspects of message delivery, without requiring any intervention from the user applications, including:
- determining who should receive the messages,
- where recipients are located,
- what happens if messages cannot be delivered.
This is made possible by the fact that DDS allows the user to specify Quality of Service
Quality of service
The quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...
(QoS) parameters as a way to configure automatic-discovery mechanisms and specify the behavior used when sending and receiving messages. The mechanisms are configured up-front and require no further effort on the user's part. By exchanging messages in a completely anonymous manner, DDS greatly simplifies distributed application design and encourages modular, well-structured programs.
DDS also automatically handles hot-swapping redundant publishers if the primary fails. Subscribers always get the sample with the highest priority whose data is still valid (that is, whose publisher-specified validity period has not expired). It automatically switches back to the primary when it recovers, too. DDS is available from different vendors with Ada
Ada (programming language)
Ada is a structured, statically typed, imperative, wide-spectrum, and object-oriented high-level computer programming language, extended from Pascal and other languages...
, 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#, and 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...
API
Application programming interface
An application programming interface is a source code based specification intended to be used as an interface by software components to communicate with each other...
s.
External links
- The OMG DDS portal
- RTI Data Distribution Service commercial implementation
- PrismTech's OpenSplice DDS commercial implementation
- The open source version of PrismTech's OpenSplice DDS
- Twin Oaks Computing's CoreDX commercial DDS implementation
- OCI's OpenDDS open source DDS implementation
- MilSOFT commercial implementation
- PocoCapsule for DDS A framework for component-based CORBA and DDS applications.
- InterCOM DDS Gallium commercial implementation
- Sparx DDS UML implementation
Space Software Italia developed a JAVA DDS version for applications based on Fixed and Mobile Cooperating Multi-Agents (Swarm Systems)