Modeling Elements of Web Service State in WSDL

1
Modeling Elements of Web Service State in WSDL

• May 12, 2003
• sggraham_at_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 lt 80 and contiguousAvailableSpace gt
  100 MB
• For the manageableResource interface
• If the lifecycleState crashed
• Access the stackTrace state element
• stackTrace is not a part of the services 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
  wsdlinterface
• 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
  XSDelement
• SDEs are declared within a WSDL interface
• ltgwsdlportType name"NCName"gt
• ltwsdldocumentation .... /gt ?
• ltwsdloperation name"NCName"gt
• ltsdserviceData name"NCName" /gt
• ltsdstaticServiceDataValuesgt?
• ltsome elementgt
• lt/sdstaticServiceDataValuesgt
• lt/gwsdlportTypegt

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Example PortType with SDEs

• ltwsdldefinitions xmlnstnsxxx
  targetNamespacexxxgt
• ltgwsdlportType name"exampleSDUse"gt
• ltwsdloperation namegt
• ltsdserviceData name"sd1"
  typexsdString
• mutabilitystatic/gt
• ltsdserviceData name"sd2"
  typetnsSomeComplexType/gt
• ltsdstaticServiceDataValuesgt
• lttnssdlgtinitValuelt/tnssd1gt
• lt/sdstaticServiceDataValuesgt
• lt/gwsdlportTypegt
• lt/wsdldefinitionsgt

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 (NotificationSourcesubscribe(expressio
  n))
• 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 gwsdlportType, but
• This facility is useful for more than just Grid
  applications
• Grid community really doesnt 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