It has become clear that a next step in the evolution
of Web services will be the ability to compose and describe the relationships
between Web services. Although differing terminology is used in the industry,
such as orchestration, collaboration, coordination, conversations, etc.,
the terms all share a common characteristic of defining linkages and
usage patterns between web services. For the purpose of this document,
and without prejudice, we use the term choreography as a moniker
to denote this space.
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 WG 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.
Two technical submissions -- WSCL, and WSCI, have recently been published by the W3C as Technical Notes. There are other industry efforts in the area of choreography languages, such as BPML (defined by BPMI.org), BPSS (defined by ebXML.org), IBM's
WSFL, MSFT's XLANG, and IBM/MSFT/BEA's BPEL4WS and their companion specifications WS-Coordination and WS-Transaction), etc.
The problems posed by the lack of a widely adopted choreography specification, the current proliferation of overlapping work, and the time required to complete this effort merit the chartering a new W3C WG now. This WG should address the choreography space encompassed by the input documents and deliverables. This WG should also coordinate with other WGs within the Web Service Activity, with the aim of developing an interoperable and open standard for Web service choreography
WSDL has proved very useful for describing a single service. Currently complex natural language describing the obligations of the participants detailing how to use a service (sequencing, state management, etc.) have to accompany a WSDL description. The next step is to partially replace these somewhat imprecise instructions with precise language. This will simplify the daunting task companies now face when trying to use web services to integrate their business processes. In a B2B context such a specification could reduce the cost of integrating with new trading partners and responding to changes in existing interfaces. In addition, creating a standard language to describe the relationships between document exchanges will be helpful to other standards bodies, such as RosettaNet or CIDX, giving them a standard infrastructure for message choreography and enabling them to focus on the core competencies relevant to their domain.
The Web Services Choreography Working Group, part of the Web Services Activity, is chartered to create the definition of a choreography, language(s) for describing a choreography, as well as the rules for composition of, and interaction among, such choreographed Web services. The language(s) should build upon the foundation of the Web Service Description Language (WSDL).
The Working Group shall start by considering the various input documents listed below and refine the scope and factorization of the choreography space. The Working Group is also expected to be aware of other work that has been published in this area, although it is not a formal input.
The Working Group shall consider, at a minimum, as input:
The Working Group shall produce the following deliverables:
A test suite
will be developed by the Working Group in order to assess advancement to
Proposed Recommendation stage and to promote interoperability. The Working
Group is expected to demonstrate two interoperable implementations during
the Candidate Recommendation phase. Conformance requirements must be
clearly stated in the specification produced.
The choreography specification(s) shall define (at a minimum) the behavior and language constructs for the following key concepts:
It is obvious that transactions, security, reliability, availability, and other such qualities are intimately related with Web service choreography, some more than others. It is not the goal of this group to define these mechanisms, but it must clearly articulate the boundaries.
Web services are composed of interfaces to applications, which can be written in different programming languages. The purpose of the Working Group is to provide a framework that supports a wide variety of applications and programming languages, and is not geared towards any programming language. Given the wide variety of programming languages, the Working Group should not define mappings to any programming languages.
These are subject to revision due to editorial needs and external scheduling issues; updates will be negotiated with the related groups and recorded on the Web Services Choreography Working Group home page. Meeting dates are mentioned here for planning purposes.
Working Group chartered
W3C Workshop on Web Services Choreography
First Working Group face-to-face meeting
First requirements document for Web services choreography
First Working Draft of the Web services choreography specification.
Candidate Recommendation for the Web services choreography specification.
Recommendation for the Web services choreography specification.
Working Group ends
The target duration of the Working Group is 2 years, through June 2004. Experience suggests that 6 months of contingency should be allowed to accommodate unexpected obstacles to progress.
XML and XML derived activities have become a strategic technology in W3C and elsewhere. Each deliverable of any Working Group must satisfy the dependencies from other W3C Working Groups before it can advance to Candidate Recommendation.
The Web Services Architecture Working Group has been chartered to create a document describing the architecture of Web services. A working draft of this document is now available. The Working Group will continue to take this document into account while designing the choreography language in order to make sure that Web services can be deployed in an optimal way, as recommended by the Web Services Architecture Working Group.
The Working Group must describe services accessible via WSDL 1.2 defined by the Web Services Description Group.
It is expected that other Working Groups will be formed to deal with different aspects of the Web services architecture. The Working Group will closely coordinate its work with any other Working Group formed within the Web Services Activity and generally in the Web services area, as well as with relevant Working Groups outside of the Web Services Activity.
The Working Group will participate in the Web Services Coordination Group.
The typing of the messages must be possible using XML Schema. While no dependencies other than the one with the XML Schema Working Group are presently identified, the Web Services Description Working Group should be prepared to coordinate with the XML Activity as necessary.
The Working Group will develop a primer and a test suite in order to improve the quality of the documents produced and their implementations.
The Internationalization Working Group will review work to ensure that principles developed by that group are consistently applied.
The work of the Working Group will be subject to review by this project.
XForms can be seen as providing a user interface for Web services. The Working Group will call for requirements from the XForms Working Group, if any.
The Web Services Choreography Working Group should liaise with at least the following groups outside W3C (see also W3C liaisons with other organizations):
ebXML Joint Co-ordination Committee
The ebXML initiative was a joint activity of UN/CEFACT (the United Nations body responsible for UN/EDIFACT) and OASIS (Organization for the Advancement of Structured Information Standards). Their charter was to develop an XML-based infrastructure for electronic commerce, with a particular focus on making connections between EDI and XML. While the original ebXML initiative's charter ended in May of 2001, the work transitioned to the respective sponsoring organizations (OASIS and UN/CEFACT) under the auspices of an MOU signed by the two in May of 2001.
UN/CEFACT (United Nations Centre for Trade Facilitation
and Electronic Business)
The International Trade and Business Processes Group (TBG) maintains ebXML Business Process Specification Schema, a metamodel for business processes that is part of the ebXML framework.
BPMI.org is a non-profit working towards establishing standards for the management of business processes that span multiple applications, corporate departments and business partners.
Workflow Management Coalition
The Workflow Management Coalition, founded in August 1993, is a non-profit, international organization of workflow vendors, users, analysts and university/research groups. The Coalition’s mission is to promote and develop the use of workflow through the establishment of standards for software terminology, interoperability and connectivity between workflow products.
To join the Web Services Choreography Working Group, please follow the instructions of section 4.2.3 of the Process Document, sending email to the Working Group Chair and the W3C Team contact. The nomination must include explicit agreement to this charter, including its goals, an IPR disclosure and the level of effort required of the representative.
Each Member organization may have at most two participants in the Working Group. Only Working Group participants may engage in formal votes on substantive issues. When a formal vote is required, each Member organization or group of related Members is allowed one vote, even though the Member may have several participants in the Working Group.
The W3C Team is expected to have at most two participants in the Working Group (including the Team contact). When a formal vote is required, the Team is allowed one vote.
Membership is also open to invited experts from the community, selected by the Chair in order to balance the technical experience of the group.
Each participant should expect to spend one day per week on work for this Working Group.
The Working Group will utilize a public mailing list <email@example.com> for its technical email communications. It is referred to in the rest of this document as the Working Group mailing list.
A Member-only mailing list <firstname.lastname@example.org> is available for administrative purposes only.
The Working Group has a home page that records the history of the group, provides access to the archives, meeting minutes, updated schedule of deliverables, membership list, and relevant documents and resources. The page is available to the public and should be maintained by the Chair in collaboration with the W3C Team contact.
The Working Group will have distributed and face-to-face meetings.
A one- to two-hour Working Group distributed meeting will be held every week. When necessary to meet agreed-upon deadlines, distributed meetings may be held twice a week.
The Working Group may schedule face-to-face meetings in a manner that maximizes co-location with events that Working Group members would be attending anyway.
Participation in meetings (distributed or face-to-face) is limited to participants in good standing and individuals invited at the discretion of the Chair to specific meetings.
Decisions taken in meetings must be announced on the Working Group mailing list. Observers may take part in decision-making at the discretion of the Chair.
Meeting records must include attendance, the results of group decisions, and action items. They must be made publicly available except for non-technical issues that do not directly affect the output of the Working Group. The Chair will decide which issues are not made public.
To be successful, we expect the Working Group to have approximately 20 to 30 active participants. A large public review group that will participate in the mailing list discussions is expected.
The Chair for the Web Services Choreography Working Group will be XXXX.
The W3C Team expects to dedicate the time of the services of one Team Contact, full-time, for the 2-year duration of the Working Group. XXXX will provide this effort.
W3C promotes an open working environment. Whenever possible, technical decisions should be made unencumbered by intellectual property right (IPR) claims. W3C's policy for intellectual property is set out in section 2.2 of the W3C Process document.
Members of the Working Group are expected to disclose any intellectual property they have in the area. This WG will work on a royalty-free basis, as defined in the W3C Current Patent Practice document. The Working Group is thus obliged to produce a specification which relies only on intellectual property available on a royalty-free basis.
If it proves impossible to produce specifications implementable on a royalty-free basis, then a Patent Advisory Group will be launched as described in the W3C Current Patent Practice document.
Members disclose patent and other IPR claims by sending email to <email@example.com>, an archived mailing list that is readable by Members and the W3C Team. Members must disclose all IPR claims to this mailing list but they may also copy other recipients. IPR disclosures are expected to be made public; Members should specify if their disclosure is confidential.