Steve Graham WS-ResourceFramework Modeling Stateful Resources With Web services OASIS WSRF TC F2F Wednesday, April 28th, 2004

© 2004 IBM Corporation 2 Motivation  Stateful entities exist in most systems Data in a purchase order Current usage agreement for resources Metrics associated with work load on a server  Hitherto: no standard way to deal with state in Web services context Each system does it in “idiosyncratic way” Integration impediment  Goal: Formalize a mechanism to represent “state” in Web services In order to help unify Grid computing, Systems management and e-business computing

© 2004 IBM Corporation 3 Scope of WS-ResourceFramework  How to represent state in a Web services context  How is state referenced and “identified” in Web services  How is state modeled in XML and WSDL  How is state accessed through Web services  How to reason about lifetime of state  How to aggregate/collect stateful resources  How to reason about fault messages

© 2004 IBM Corporation 4 What is a Web Service ?  An operation execution component made available at an endpoint address A service is defined in terms of the operations it implements –An operation is defined in terms of a message exchange The supported set of messages exchanges (operations) implemented by a service may be described as a WSDL portType The Web service itself is typically stateless  Accessible through use of a WS-Addressing Endpoint Reference  Lifecycle of a Web service typically described in terms of “deployment”

© 2004 IBM Corporation 5 What do we mean by Stateful Resource ?  A specific set of state data expressible as an XML document;  Has a well-defined identity and lifecycle; and  Known to, and acted upon, by one or more Web services.  Many possible implementations Files, Database tables, EJB Entities, XML documents, Composed from multiple data sources, etc.  Lifecycle expressed in terms of resource creation and destruction Multiple independent instances may be created and destroyed Identity is assigned at creation time

© 2004 IBM Corporation 6 WS-Addressing: Referencing Web services  Standardizes the representation of the address of a Web service deployed at a given network endpoint  A WS-Addressing endpoint reference is an XML serialization of a network-wide pointer to a Web service  EPRs can be used to pass services to other services by reference  Dynamic generation and customization of service endpoint descriptions  Identification and description of specific service instances that are created as the result of stateful interactions  An EPR contains: Service address (wsa:Address) Metadata associated with the Web service such as service description information (WSDL) Policy information related to the use of the service Reference properties, which can be used to identify specific stateful resource instances associated with the Web service at the endpoint address (wsa: ReferenceProperties)

© 2004 IBM Corporation 7 Contents of EndpointReference

© 2004 IBM Corporation 8 WS-Resource  WS-Resource: Web service + associated resource In other words: – A resource with an associated Web service  A WS-Resource has: Identity: Can be uniquely identified/referenced Lifetime: Often created & destroyed by clients State: Can be projected as an XML document Type: Its Web service interface  An EPR “ points to ” a WS-Resource WS-Resource Qualified Endpoint Reference Implied Resource Pattern

© 2004 IBM Corporation 9 The WS-Resource Qualified Endpoint Reference  An endpoint reference containing a WS-Resource identifier is a WS-Resource-qualified endpoint reference.

© 2004 IBM Corporation 10 WS-Resource Identifier  The WS-Resource identifier is a “lookup key” the WS- Resource to be used in the execution of the request message The set of reference properties  The content of the WS-Resource identifier is opaque to the service requestor The service requestor’s applications should not examine or attempt to interpret the contents of the WS-Resource identifier The WS-Resource identifier is meaningful only to the Web service  From the point of view of the service requestor: EPR is a pointer to the Web service + WS-Resource In other words, the EPR represents a pointer to a WS-Resource accessible through a Web service

© 2004 IBM Corporation 11 WS-Resource Relationship Cardinality  A Web service can execute message exchanges against zero or more WS-Resources of a given type  One Stateful resource can be “associated” with multiple Web services Different interfaces, or same interface for redundancy  At the type level, a WSDL 1.1 portType, defining the interface to a Web service, can be associated with at most one “kind” or “type” of WS- Resource  One “kind” or “type” of WS-Resource can be associated with many WSDL 1.1 portTypes A C WS1 B WS2