Service choreography

Last updated

Service choreography in business computing is a form of service composition in which the interaction protocol between several partner services[ clarification needed ] is defined from a global perspective. [1] The idea underlying the notion of service choreography can be summarised as follows:

Contents

"Dancers dance following a global scenario without a single point of control"

That is, at run-time each participant in a service choreography executes its part according to the behavior of the other participants. [2] A choreography's role specifies the expected messaging behavior of the participants that will play it in terms of the sequencing and timing of the messages that they can consume and produce. [3]

Choreography describes the sequence and conditions in which the data is exchanged between two or more participants in order to meet some useful purpose. [4]

Service choreography and service orchestration

Service choreography is better understood through the comparison with another paradigm of service composition: service orchestration. On one hand, in service choreographies the logic of the message-based interactions among the participants is specified from a global perspective. In service orchestration, on the other hand, the logic is specified from the local point of view of one controlling participant, called the orchestrator. In the service orchestration language BPEL, for example, the specification of the service orchestration (e.g. the BPEL process file) is a workflow that can be deployed on the service infrastructure (for example a BPEL execution engine like Apache ODE). The deployment of the service orchestration specification transforms a workflow into a composite service. [5]

In a sense, service choreography and orchestrations are two sides of the same coin. On one hand, the roles of a service choreography can be extracted as service orchestrations through a process called projection. [6] Through projection it is possible to realize skeletons, i.e. incomplete service orchestrations that can be used as baselines to realize the web services that participate to the service choreography. On the other hand, already existing service orchestrations may be composed in service choreographies.

Enactment of service choreographies

Service choreographies are not executed: they are enacted. A service choreography is enacted when its participants execute their roles. [7] That is, unlike service orchestration, service choreographies are not run by some engine on the service infrastructure, but they “happen" when their roles are executed. This is because the logic of the service choreography is specified from a global point of view, and thus it is not realized by one single service like in service orchestration.

The key question which much of the research into choreography seeks to answer is this: Suppose a global choreography is constructed that describes the possible interactions between the participants in a collaboration. What conditions does the choreography need to obey if it is to be guaranteed that the collaboration succeeds? Here, succeeds means that the emergent behaviour that results when the collaboration is enacted, with each participant acting independently according to its own skeleton, exactly follows the choreography from which the skeletons were originally projected. When this is the case, the choreography is said to be realizable. [8] In general, determining realizability of a choreography is a non-trivial question, particularly where the collaboration uses asynchronous messaging and it is possible for different participants to send messages simultaneously.

Service choreography languages

In the ambit of the specifications concerning Web services, the following specifications have focused on defining languages to model service choreographies:

Moreover, the OMG specification BPMN version 2.0 includes diagrams to model service choreographies. [9]

Academic proposals for service choreography languages include:

Moreover, a number of service choreography formalisms have been proposed based on:

Web service choreography

Web service choreography (WS-Choreography) is a specification by the W3C defining an XML-based business process modeling language that describes collaboration protocols of cooperating Web Service participants, in which services act as peers, and interactions may be long-lived and stateful. (Orchestration is another term with a very similar, but still different meaning.)

The main effort to get a choreography, The W3C Web Services Choreography Working Group, was closed on 10 July 2009 [24] leaving WS-CDL as a Candidate Recommendation.

"Many presentations at the W3C Workshop on Web services of 11–12 April 2001 pointed to the need for a common interface and composition language to help address choreography. The Web Services Architecture Requirements Working Draft created by the Web Services Architecture Working Group also lists the idea of Web service choreography capabilities as a Critical Success Factor, in support of several different top-level goals for the nascent Web services architecture".

The problem of choreography was of great interest to the industry during that time; efforts such as WSCL (Web Service Conversation Language) and WSCI (Web Service Choreography Interface) were submitted to W3C and were published as Technical Notes. Moreover, complementary efforts were launched: [25]

"In June 2002, Intalio, Sun, BEA and SAP released a joint specification named Web Services Choreography Interface (WSCI). This specification was also submitted to W3C as a note in August 2002. W3C has since formed a new Working Group called Web Services Choreography Working Group within the Web services Activity. The WSCI specification is one of the primary inputs into the Web Services Choreography Working Group which published a Candidate Recommendation on WS-CDL version 1.0 on November 9th, 2005". "XLang, WSFL and WSCI are no longer being supported by any standard organization or companies. BPEL replaced Xlang and WSFL WSCI was superseded by WS-CDL".

The upcoming Business Process Modeling Notation version 2.0 will introduce diagrams for specifying service choreographies. [9]

The academic field has put forward other service choreography languages, for example Let's Dance, [10] BPEL4Chor [11] and MAP. [19]

Paradigms of service choreographies

Service choreographies specify message-based interactions among participants from a global perspective. In the same way as programming languages can be grouped into programming paradigms, service choreography languages can be grouped in styles: [26]

Research projects on choreographies

There are several active research projects on the topic of service choreography.

See also

Related Research Articles

A web service (WS) is either:

The Organization for the Advancement of Structured Information Standards is a nonprofit consortium that works on the development, convergence, and adoption of open standards for cybersecurity, blockchain, Internet of things (IoT), emergency management, cloud computing, legal data exchange, energy, content technologies, and other areas.

The Web Services Business Process Execution Language (WS-BPEL), commonly known as BPEL, is an OASIS standard executable language for specifying actions within business processes with web services. Processes in BPEL export and import information by using web service interfaces exclusively.

The High Level Architecture (HLA) is a standard for distributed simulation, used when building a simulation for a larger purpose by combining (federating) several simulations. The standard was developed in the 1990s under the leadership of the US Department of Defense and was later transitioned to become an open international IEEE standard. It is a recommended standard within NATO through STANAG 4603. Today the HLA is used in a number of domains including defense and security and civilian applications.

<span class="mw-page-title-main">Business Process Model and Notation</span> Graphical representation for specifying business processes

Business Process Model and Notation (BPMN) is a graphical representation for specifying business processes in a business process model.

<span class="mw-page-title-main">XPDL</span>

The XML Process Definition Language (XPDL) is a format standardized by the Workflow Management Coalition (WfMC) to interchange business process definitions between different workflow products, i.e. between different modeling tools and management suites. XPDL defines an XML schema for specifying the declarative part of workflow / business process.

Business Process Modeling Language (BPML) is an XML-based language for business process modeling. It was maintained by the Business Process Management Initiative (BPMI) until June 2005 when BPMI and OMG announced the merger of their respective Business Process Management (BPM) activities to form the Business Modeling and Integration Domain Task Force. It is deprecated since 2008. BPML was useful to OMG in order to enrich UML with process notation.

The Business Process Definition Metamodel (BPDM) is a standard definition of concepts used to express business process models, adopted by the OMG. Metamodels define concepts, relationships, and semantics for exchange of user models between different modeling tools. The exchange format is defined by XSD and XMI, a specification for transformation of OMG metamodels to XML. Pursuant to the OMG's policies, the metamodel is the result of an open process involving submissions by member organizations, following a Request for Proposal (RFP) issued in 2003. BPDM was adopted in initial form in July 2007, and finalized in July 2008.

<span class="mw-page-title-main">Apache ODE</span>

Apache ODE is a software coded in Java as a workflow engine to manage business processes which have been expressed in the Web Services Business Process Execution Language (WS-BPEL) via a website. It was made by the Apache Software Foundation and released in a stable format on March 23, 2018. The software principally communicates with one or more Web services, sending and receiving messages, manipulating data and handling exceptions (errors) as defined by any given process. The engine is capable of running both long and short living processes to coordinate all the services that make up a service or application (orchestration).

BPELscript is a language to specify BPEL processes. It provides a compact syntax inspired by scripting languages such as JavaScript and Ruby and a full coverage of all features provided by BPEL.

<span class="mw-page-title-main">Wil van der Aalst</span> Dutch computer scientist and professor

Willibrordus Martinus Pancratius van der Aalst is a Dutch computer scientist and full professor at RWTH Aachen University, leading the Process and Data Science (PADS) group. His research and teaching interests include information systems, workflow management, Petri nets, process mining, specification languages, and simulation. He is also known for his work on workflow patterns.

<span class="mw-page-title-main">Web Services Description Language</span> XML-based interface description language

The Web Services Description Language is an XML-based interface description language that is used for describing the functionality offered by a web service. The acronym is also used for any specific WSDL description of a web service, which provides a machine-readable description of how the service can be called, what parameters it expects, and what data structures it returns. Therefore, its purpose is roughly similar to that of a type signature in a programming language.

In philosophy, a process ontology refers to a universal model of the structure of the world as an ordered wholeness. Such ontologies are fundamental ontologies, in contrast to the so-called applied ontologies. Fundamental ontologies do not claim to be accessible to any empirical proof in itself, but to be a structural design pattern, out of which empirical phenomena can be explained and put together consistently. Throughout Western history, the dominating fundamental ontology is the so-called substance theory. However, fundamental process ontologies are becoming more important in recent times, because the progress in the discovery of the foundations of physics spurred the development of a basic concept able to integrate such boundary notions as "energy," "object", and those of the physical dimensions of space and time.

Web Services Flow Language 1.0 (WSFL) was an XML programming language proposed by IBM in 2001 for describing Web services compositions. Language considered two types of compositions. The first type was for describing business processes as a collection of web services and the second was for describing interactions between partners. WSFL was proposed to be layered on top of Web Services Description Language.

<span class="mw-page-title-main">Jolie (programming language)</span>

Jolie is an open-source programming language for developing distributed applications based on microservices. In the programming paradigm proposed with Jolie, each program is a service that can communicate with other programs by sending and receiving messages over a network. Jolie supports an abstraction layer that allows services to communicate using different mediums, ranging from TCP/IP sockets to local in-memory communications between processes.

Executable choreography represents a decentralized form of service composition, involving the cooperation of several individual entities. It is an improved form of service choreography. Executable choreographies can be intuitively seen as arbitrary complex workflows that get executed in systems belonging to multiple organisations or authorities.

<span class="mw-page-title-main">Frank Leymann</span> German computer scientist and mathematician

Frank Leymann is a German computer scientist and mathematician. He is professor of computer science at the University of Stuttgart, Germany, and director and founder of the Institute of Architecture of Application Systems (IAAS).

References

  1. ↑ S-Cube Knowledge Model: Service Choreography
  2. ↑ Chris Peltz: Web Services Orchestration and Choreography. IEEE Computer (COMPUTER) 36(10):46-52 (2003)
  3. ↑ Jianwen Su, Tevfik Bultan, Xiang Fu, Xiangpeng Zhao: Towards a Theory of Web Service Choreographies. WS-FM 2007:1-16
  4. ↑ "WS Choreography Model Overview". 24 March 2004. Retrieved 16 February 2019.
  5. ↑ Arellanes, Damian; Lau, Kung-Kiu (2017). "Exogenous Connectors for Hierarchical Service Composition". 2017 IEEE 10th Conference on Service-Oriented Computing and Applications (SOCA). Kanazawa: IEEE: 125–132. doi:10.1109/SOCA.2017.25. ISBN   9781538613269. S2CID   31211787.
  6. ↑ Hongli Yang, Xiangpeng Zhao, Chao Cai, Zongyan Qiu: "Exploring the Connection of Choreography and Orchestration with Exception Handling and Finalization/Compensation". FORTE 2007:81-96
  7. ↑ Howard Foster, Sebastián Uchitel, Jeff Magee, Jeff Kramer: Model-Based Analysis of Obligations in Web Service Choreography. AICT/ICIW 2006:149
  8. ↑ Ashley McNeile: Protocol Contracts with Application to Choreographed Multiparty Collaborations. Service Oriented Computing and Applications Volume 4, Number 2, 109-136 (2010)
  9. 1 2 Jack Vaughan: BPMN 2.0 adds notation to handle BPM choreography. SearchSOA.com, 22 Oct 2009
  10. 1 2 3 Johannes Maria Zaha, Alistair P. Barros, Marlon Dumas, Arthur H. M. ter Hofstede: Let's Dance: A Language for Service Behavior Modeling. OTM Conferences 2006:145-162
  11. 1 2 3 Gero Decker, Oliver Kopp, Frank Leymann, Mathias Weske: BPEL4Chor: Extending BPEL for Modeling Choreographies. ICWS 2007:296-303
  12. ↑ "Chor Programming Language".
  13. ↑ Carbone, Marco; Montesi, Fabrizio (2013). Deadlock-freedom by design: Multiparty Asynchronous Global Programming. doi:10.1145/2429069.2429101.
  14. ↑ Gero Decker, Mathias Weske: Local Enforceability in Interaction Petri Nets. BPM 2007:305-319
  15. ↑ Karsten Schmidt: Controllability of Open Workflow Nets. EMISA 2005:236-249
  16. ↑ Nadia Busi, Roberto Gorrieri, Claudio Guidi, Roberto Lucchi, Gianluigi Zavattaro: Choreography and Orchestration Conformance for System Design. COORDINATION 2006:63-81
  17. ↑ Tevfik Bultan, Jianwen Su, Xiang Fu: Analyzing Conversations of Web Services. IEEE Internet Computing (INTERNET) 10(1):18-25 (2006)
  18. ↑ Michele Mancioppi, Manuel Carro, Willem-Jan van den Heuvel, Mike P. Papazoglou: Sound Multi-party Business Protocols for Service Networks. ICSOC 2008:302-316
  19. 1 2 Adam Barker, Christopher D. Walton, David Robertson: Choreographing Web Services. IEEE Transactions on Services Computing, volume 2, number 2, pages 152-166, IEEE Computer Society, April–June 2009
  20. ↑ ShuiGuang Deng, Zhaohui Wu, Mengchu Zhou, Ying Li, Jian Wu: Modeling Service Compatibility with Pi-calculus for Choreography. ER 2006:26-39
  21. ↑ Paolo Besana, Adam Barker: An Executable Calculus for Service Choreography. OTM Conferences 2009:373-380
  22. ↑ Raman Kazhamiakin, Marco Pistore: Analysis of Realizability Conditions for Web Service Choreographies. FORTE 2006:61-76
  23. ↑ Zongyan Qiu, Xiangpeng Zhao, Chao Cai, Hongli Yang: Towards the theoretical foundation of choreography. WWW 2007:973-982
  24. ↑ Web Services Choreography Working Group at W3
  25. ↑ Charter
  26. ↑ Gero Decker, Oliver Kopp, Alistair P. Barros: An Introduction to Service Choreographies (Servicechoreographien - eine Einführung). it - Information Technology (IT) 50(2):122-127 (2008)
  27. ↑ S-Cube Knowledge Model: Interaction Choreography Model
  28. ↑ S-Cube Knowledge Model: Interconnected Interface Choreography Model
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.