W3C has acknowledged receipt of a 2002-02-04 submission from the Hewlett-Packard Company for a Web Services Conversation Language (WSCL). The published Note "proposes a simple conversation language standard that can be used for various Web-service protocols and frameworks. It focuses on modeling the sequencing of the interactions or operations of one interface and fills the gap between mere interface definition languages that do not specify any choreography and more complex process or flow languages that describe complex global multi-party conversations and processes." The Web Services Conversation Language "allows the abstract interfaces of Web services, i.e., the business level conversations or public processes supported by a Web service, to be defined. WSCL specifies the XML documents being exchanged, and the allowed sequencing of these document exchanges. WSCL conversation definitions are themselves XML documents and can therefore be interpreted by Web services infrastructures and development tools. WSCL may be used in conjunction with other service description languages like WSDL; for example, to provide protocol binding information for abstract interfaces, or to specify the abstract interfaces supported by a concrete service." The WSCL submission will be brought to the attention of W3C's Web Services Architecture Working Group and to the Web Services Description Working Group; it will also be brought to the attention of the Web Ontology Working Group as a potential use case for the Web Ontology language designed.

An earlier version of WSCL was released through HP Web Services (May 2001).

Bibliographic information: Web Services Conversation Language (WSCL) 1.0. W3C Note 14-March-2002. Authors from Hewlett-Packard Company: Arindam Banerji, Claudio Bartolini, Dorothea Beringer, Venkatesh Chopella, Kannan Govindarajan, Alan Karp, Harumi Kuno, Mike Lemon, Gregory Pogossiants, Shamik Sharma, and Scott Williams. Version URL: http://www.w3.org/TR/2002/NOTE-wscl10-20020314/. Latest version URL: http://www.w3.org/TR/wscl10/.

WSCL description from the W3C staff comment: "A single communication between two parties in the context of Web services is usually part of a larger application-level process, i.e., a complex set of interactions. The Web Services Conversation Language (WSCL) 1.0 allows the description of sequences interactions with a Web service, called conversations. The format of the XML documents exchanged are called document type descriptions and are expressed as references to XML schemas. The exchanges of inbound and outbound documents with a Web service are called interactions. An application-level communication is likely to be composed of a sequence of interactions and can be modeled as a UML activity diagram. WSCL allows description of the transitions from one interaction (activity) to another, which can be based on the result of an interaction. WSCL doesn't address the protocol binding aspect of the interactions nor the instantiation of the abstract interfaces described. The specification includes a section about how to combine WSCL with WSDL, which addresses those aspects." [excerpt only]

Extending WSCL: "The WSCL specification contains the smallest possible set of elements and attributes to describe conversations. This set is sufficient to model many of the conversations needed for Web services. However, there are more complex B2B interactions that need additional capabilities from a conversation definition language. Such additional requirements include the following examples: (1) Defining document types that have non-XML content; for example, binary attachments; (2) Explicit description of roles of participants; (3) Multi-party conversations with three or more participants or roles; (4) Expressing timeouts and other quality of service characteristics of individual interactions; (5) Expressing more complex SourceInteractionConditions; for example, listing several documents, excluding documents, or even referencing the content of documents; (6) Events, i.e., interactions that can occur at any time within a conversation instance; (7) Recursive conversations, aggregating conversations into larger conversations; (6) Sub-typing and extending existing conversation definitions." [from the v1.0 Note]