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Modeling Elements of Web Service State in WSDL

Modeling Elements of Web Service State in WSDL. May 12, 2003 sggraham@us.ibm.com Global Grid Forum. Situation. In Grid computing (particularly infrastructure) Modeling stateful Web service instances (with identity) Certain services have complex state

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Modeling Elements of Web Service State in WSDL

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  1. Modeling Elements of Web Service State in WSDL May 12, 2003 sggraham@us.ibm.com Global Grid Forum

  2. Situation • In Grid computing (particularly infrastructure) • Modeling stateful Web service instances (with identity) • Certain services have complex state • Dozens (perhaps many dozens) of state elements • Many of these state elements need to be publicly accessible • get, set, query, subscribe for state change notification

  3. Accessing Publicly Available State • We would like service requestors (for example management applications) to be able to: • Access publicly available state data from Web services • We would like service providers to: • Declare which elements of their state are publicly accessible • Modeled at the interface level • Which elements are readable, writeable, subscribable • Declare operations that allow get, set, query across multiple elements, and subscribe • Declare “dynamic state data elements” • e.g. elements of state that are available only because of a particular service life cycle value.

  4. Examples • For all the instances of “diskDrive” interface • Find me all the ones where • percentFull < 80% and contiguousAvailableSpace > 100 MB • For the “manageableResource” interface • If the lifecycleState = “crashed” • Access the “stackTrace” state element • “stackTrace” is not a part of the service’s state in most circumstances

  5. Option 1 – model as operations • Use getters/setters to access “attributes” • Similar to JavaBeans pattern • no new concepts • explosion of # messages, parts and operations in the interface • Relies on programmer adhering to a convention • No simple multi-attribute query • At best only hard coded queries • No notion of “dynamic” state elements

  6. Option 2 – Model as First Class Concept • Introduce an “Attribute” concept to wsdl:interface • Similar to attribute in CORBA IDL • Core idea: • Elements of publicly available state are modeled using XML Schema element • State of a Web service instance is modeled “logically” as an XML instance document • Define operations: get, set, query, [subscribe] • Elements of state are modeled with the interface definition as attributes • Use attributes to convey state and meta-data of the service • Client proxy generators can still generate type-specific getters/setters (if they want)

  7. In OGSI – ServiceData Elements • Modeled state elements as “serviceData elements” • SDE is an extension and restriction of XSD:element • SDEs are declared within a WSDL interface <gwsdl:portType name="NCName"> * <wsdl:documentation .... /> ? <wsdl:operation name="NCName"> * … <sd:serviceData name="NCName" … /> * <sd:staticServiceDataValues>? <some element>* </sd:staticServiceDataValues> … </gwsdl:portType>

  8. Example PortType with SDEs <wsdl:definitions xmlns:tns=”xxx” targetNamespace=”xxx”> <gwsdl:portType name="exampleSDUse"> * <wsdl:operation name=…> … <sd:serviceData name="sd1" type=”xsd:String” mutability=”static”/> <sd:serviceData name="sd2" type=”tns:SomeComplexType”/> … <sd:staticServiceDataValues> <tns:sdl>initValue</tns:sd1> </sd:staticServiceDataValues> </gwsdl:portType> … </wsdl:definitions>

  9. SDEs in OGSI • SDEs are inherited down an interface inheritance hierarchy • Operations are defined in the GridService interface (base) • get (findServiceData(expression)) • set (setServiceData(expression)) • subscribe (NotificationSource::subscribe(expression)) • Dynamic service data is supported • GridService has a “serviceDataName” SDE • SDE values are conveyed using a “container element”

  10. Concerns • This is ok to model in gwsdl:portType, but: • This facility is useful for more than just Grid applications • Grid community really doesn’t want this feature separate from Web services community • Interoperability, tooling, runtimes, adoption

  11. Proposal • W3C Web Services Description Working Group form a task force to examine the concept of modeling elements of publicly available state data in WSDL 1.2 • Concept and requirements • Conceptual model • Syntax • Operations • Deliver final conclusions to entire WG • NO LATER THAN Toronto F2F

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