Data Distribution Service: Difference between revisions

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{{Short description|Object Management Group standard}}

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The '''Data Distribution Service''' ('''DDS''') for real-time systems is an [[Object Management Group]] (OMG) [[machine-to-machine]] (sometimes called [[middleware]] or connectivity framework) standard that aims to enable [[Safety-critical|dependable]], [[Many-task computing|high-performance]], [[interoperable]], [[Real-time computing|real-time]], [[Scalability|scalable]] [[data exchange]]s using a [[publish–subscribe pattern]].

DDS addresses the real-time data exchange needs of applications likewithin aerospace and, defense, [[air-traffic control]], [[autonomous vehicles]], medical devices, robotics, power generation, simulation and testing, [[smart grid]] management, transportation systems, and other applications that require real-time data exchange.

== Architecture ==

=== The Conceptual Model ===

=== The Conceptual Model ===

Conceptually, DDS builds a Distributed Global Data Space where applications interact and cooperate by sharing data in Secure, Real-time and Fault-tolerant way. Applications that take the responsibility to produce data endorse the role of Writers, those that consume it are Readers. Applications can filter or query data (in SQL) as if they are interacting with a real-time and an in-memory database.

With DDS, Data and their associated Quality of Services are the only contract that bounds and integrate distributed the applications together. Data can represent Device and system States, Commands or Replies, Video and Audio stream, Documents and Messages, etc ... From that perspective, DDS helps to build a Data-Centric System as opposed to Service-Oriented System where applications interact by invoking their mutual interfaces.

Although there is a unique Global Data Space, in a DataCentric Middleware each Data Reader and Data writer can have or build its unique view of the data.

DDS helps to build decoupled and distributed architectures where Applications do not have to expose either their ___location, their APIs, their internal behaviour nor they need to be active and alive at the same time. With DDS, the decoupling is bidimensional, it happens both in Space and Time. Applications developers focus on the data they provide and the data they require and do not need to deal with the underlying networking technologies in use.

To build and share the Global Data Space DDS relies on the Publisher and Subscriber communication paradigm.

The Global data space lives in the notion of a Domain. A DDS ___domain is an administrative boundary that limits the scope of the data dissemination within the network. Only applications that live in the same ___domain can share data and can communicate. A DDS partition organises the Global data space and the datasets it contains in logical groups to form hierarchies, disjoint groups or networked groups.

=== The Engineering Model ===

DDS is a networking [[middleware]] that simplifies complex [[computer network programming|network programming]]. It implements a [[publish–subscribe pattern]] for sending and receiving data, events, and commands among the [[node (networking)|node]]s. Nodes that produce information (publishers) create "topics" (e.g., temperature, ___location, pressure) and publish "samples". DDS delivers the samples to subscribers that declare an interest in that topic.

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* what happens if messages cannot be delivered

DDS allows the user to specify [[quality of service]] (QoS) parameters to configure discovery and behavior mechanisms up-front. By exchanging messages anonymously, DDS simplifies distributed applications and encourages modular, well-structured programs. {{citation needed|date=October 2019}}

DDS also automatically handles hot-swapping redundant publishers if the primary fails. {{citation needed|date=October 2019}} Subscribers always get the sample with the highest priority whose data is still valid (that is, whose publisher-specified validity period has not expired){{citation needed|date=January 2024}}. It automatically switches back to the primary when it recovers, too{{citation needed|date=January 2024}}.

=== Interoperability ===

Both commercialproprietary and [[open-source software]] implementations of DDS are available. These include [[application programming interface]]s (APIs) and libraries of implementations in [[Ada (programming language)|Ada]], [[C (programming language)|C]], [[C++]], [[C Sharp (programming language)|C#]], [[Java (programming language)|Java]], [[Python (programming language)|Python]], [[Scala (programming language)|Scala]], [[Lua (programming language)|Lua]], [[Pharo]] and, [[Ruby (programming language)|Ruby]]., and [[Rust (programming language)|Rust]].

DDS vendors participated in interoperability demonstrations at the OMG Spring technical meetings from 2009 to 2013.<ref name="2009DemoNotes">{{Cite web|url=http://www.omg.org/news/meetings/GOV-WS/pr/rte-pres/ddsi-demo.pdf|title=DDS Interoperability Demo|author=Angelo Corsaro, Gerardo Pardo-Castellote and Clark Tucker|date=August 12, 2009|publisher=Object Management Group|archiveurlarchive-url=https://web.archive.org/web/20110915193450/http://www.omg.org/news/meetings/GOV-WS/pr/rte-pres/ddsi-demo.pdf|archivedatearchive-date=September 15, 2011|url-status=dead|accessdateaccess-date=November 9, 2016}}</ref><ref name="2010DemoNotes">{{Cite web|url=https://d2vkrkwbbxbylk.cloudfront.net/sites/default/files/dds_interop_demo_santa_clara_dds_2010_12_04.pdf|title=DDS Interoperability Demo December 2010|date=December 11, 2010|publisher=Real-Time Innovations, Inc|accessdateaccess-date=November 9, 2016}}</ref><ref name="2011DemoNotes">2011, March 2011, https://community.rti.com/content/presentation/omg-dds-interoperability-demo-2011</ref><ref name="2012DemoNotes">2012, March 2012, https://community.rti.com/content/presentation/omg-dds-interoperability-demo-2012</ref><ref name="2013DemoNotes">2013, March 2013, http://www.slideshare.net/GerardoPardo/dds-interoperability-demo-2013-washington-dc</ref><ref>{{Cite web|url=https://www.youtube.com/watch?v=Bn56V0NLW1E |archive-url=https://web.archive.org/web/20140107013946/http://www.youtube.com/watch?v=Bn56V0NLW1E |archive-date=2014-01-07 |url-status=dead|title=DDS Interoperability Demonstration|date=December 14, 2010|work=video|publisher=Real-Time Innovations|accessdateaccess-date=November 9, 2016}}</ref>

During demos, each vendor published and subscribed to each other's topics using a test suite called the shapes demo. For example, one vendor publishes information about a shape and the other vendors can subscribe to the topic and display the results on their own shapes display. Each vendor takes turns publishing the information and the other subscribe.

Two things made the demos possible: the DDS-I or Real-Time Publish-Subscribe (RTPS) protocol,<ref name="RtpsRef">{{Cite web|url=http://www.omg.org/spec/DDSI-RTPS/|title=The Real-time Publish-Subscribe Wire Protocol DDS Interoperability Wire Protocol Specification (DDSI-RTPS)|last=|first=|date=May 2019|website=|url-status=live|archive-url=|archiveaccess-date=|accessdate=October 28, 2019}}</ref> and the agreement to use a common model.

[[File:Notional OMG DDS Interoperability.jpg|thumb|upright=2.4|OMG Data Distribution Service interoperability]]

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== History ==

Development of the DDS specification started in 2001. It was developed by Real-Time Innovations, a US government contractor, and [[Thales Group]], a French defense company. In 2004, the [[Object Management Group]] (OMG) published DDS version 1.0.<ref>{{Cite web |title= Data Distribution Service (DDS), Version 1.0 |date= December 2, 2004 |publisher= Object Management Group |url= http://www.omg.org/spec/DDS/1.0 |accessdateaccess-date= November 9, 2016 }}</ref> Version 1.1 was published in December 2005,<ref>{{Cite web |title= Data Distribution Service (DDS), Version 1.1 |date= December 4, 2005 |url= http://www.omg.org/spec/DDS/1.1 |accessdateaccess-date= November 9, 2016 }}</ref> 1.2 in January 2007,<ref>{{Cite web |title= Data Distribution Service (DDS), Version 1.2 |date= January 1, 2007 |url= http://www.omg.org/spec/DDS/1.2 |accessdateaccess-date= November 9, 2016 }}</ref> and 1.4 in April 2015.<ref>{{Cite web |title= Data Distribution Service (DDS), Version 1.4 |date= April 10, 2015 |url= http://www.omg.org/spec/DDS/1.4 |accessdateaccess-date= November 9, 2016 }}</ref>

DDS is covered by several US patents,<ref>[https://wwwpatents.google.com/patentspatent/US8874686 US Patent US8874686]</ref><ref>[httphttps://wwwpatents.google.com/patentspatent/US8671135 US Patent US8671135]</ref><ref>[httphttps://wwwpatents.google.com/patentspatent/US8150988 US Patent US8150988]</ref><ref>[httphttps://wwwpatents.google.com/patentspatent/US9015672 US Patent US9015672]</ref> among others.

The DDS specification describes two levels of interfaces:

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The specification provides mappings for the [[application programming interface]] (API) specified in DDS-XTypes, and accessing [[quality of service]] (QoS) profiles specified in DDS-CCM.

Extensible and Dynamic Topic Types for DDS (DDS-XTypes) provided support for data-centric publish-subscribe communication where topics are defined with specific data structures. To be ''extensible'', DDS topics use data types defined before compile- time and used throughout the DDS global data space. This model is desirable when static type checking is useful.<ref>Extensible and Dynamic Topic Types for DDS (DDS-XTypes), 1.0, formal/2012-11-10, November 2012, http://www.omg.org/spec/DDS-XTypes/1.0/PDF</ref>

A [[Unified Modeling Language]] (UML) profile specified DDS domains and topics to be part of the analysis and design modeling.<ref>UML Profile for Data Distribution, version: 1.0, http://www.omg.org/cgi-bin/doc?ptc/10-05-17.pdf </ref> This specification also defined how to publish and subscribe objects without first describing the types in another language, such as XML or OMG IDL.<ref>DDS-Java: Java 5 Language PSM for DDSVersion 1.0, ptc/2012-12-01, March 2013 http://www.omg.org/spec/DDS-Java/1.0/Beta3/PDF</ref>

An [[interface definition language]] (IDL) was specified in 2014 independently from the [[Common Object Request Broker Architecture]] (CORBA) specification chapter 3. This IDL 3.5 was compatible with the CORBA 3 specification, but extracted as its own specification allowing it to evolve independently from CORBA.<ref>{{Cite web |title= Interface Definition Language (IDL), Version 3.5 |date= March 1, 2014 |publisher= OMG |url= http://www.omg.org/spec/IDL35/3.5/ |accessdateaccess-date= November 9, 2016 |archive-url= https://web.archive.org/web/20170121033326/http://www.omg.org/spec/IDL35/3.5/ |archive-date= January 21, 2017 |url-status= dead }}</ref>

Other protocols to be mentioned are: DDS-XRCE (DDS for eXtremely Resource Constrained Environments), this specification protocol allows the communication between devices of limited resources, like microcontroller for example and a DDS network. It makes publishing and subscribing to topics via an intermediate service in a DDS ___domain possible <ref>{{Cite web|title=About the DDS For Extremely Resource Constrained Environments Specification Version 1.0|url=https://www.omg.org/spec/DDS-XRCE|access-date=2021-03-12|website=www.omg.org}}</ref> and DDS-RPC (RPC Over DDS) which defines Remote Procedure Calls. These provide a bidirectional request/reply communication and determine distributed services, and are detailed using a service interface. It also supports both synchronous and asynchronous method invocation.<ref>{{Cite web|title=About the RPC Over DDS Specification Version 1.0|url=https://www.omg.org/spec/DDS-RPC/1.0|access-date=2021-03-12|website=www.omg.org}}</ref>

Starting with DDS version 1.4 in 2015, the optional DLRL layer was moved to a separate specification.<ref>{{Cite web |title= DDS Data Local Reconstruction Layer (DDS-DLRL) |date= April 2015 |url= http://www.omg.org/spec/DDS-DLRL/ |accessdate= November 9, 2016 }}</ref>

== Commercial Editors and Opensource Editions ==

Starting with DDS version 1.4 in 2015, the optional DLRL layer was moved to a separate specification.<ref>{{Cite web |title= DDS Data Local Reconstruction Layer (DDS-DLRL) |date= April 2015 |url= http://www.omg.org/spec/DDS-DLRL/ |accessdateaccess-date= November 9, 2016 }}</ref>

Several editors provide OMG DDS compliant implementations, namely:

* [[ADLINK]], [https://www.adlinktech.com/en/data-distribution-service]

* [[eProsima]], [https://www.eprosima.com/index.php/]

* [[Kongsberg]], [https://kongsberggeospatial.com/]

* [[Milsoft]], [http://www.milsoft.com.tr/]

* [[Object Groups Inc]], [https://objectcomputing.com/ ]

* [[RTI]], [https://www.rti.com/en/]

* [[Twinoaks]], [http://www.twinoakscomputing.com/]

Some DDS implementations are opensource with commercially support offerings, such as:

* [[Cyclone DDS]], [http://github.com/eclipse-cyclonedds/cyclonedds]

* [[FastRTPS]], [https://github.com/eProsima/Fast-DDS]

* [[OpenDDS]], [https://github.com/objectcomputing/OpenDDS]

* [[Opensplice]], DDS community edition]] https://github.com/ADLINK-IST/opensplice

== See also ==

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* [[Middleware]]

* [[Open architecture computing environment]]

* [[Object Management Group]] (OMG), the standards body that developed the specification

== References ==

{{Reflist|30em}}

{{Ambient intelligence}}