1. Formal Specification Of Web Services For Dependable Systems contribution to the PISA Workshop (25. – 27. 11. 2002) on the IP DeSIRE and the NoE DeFINE Prof. Dr. F. VOGT TELEMATIK TU Hamburg-Harburg Slides prepared by Marcus Venzke

2. 2 WSDL is Not Enough! Interface = Contract! Described in WSDL In WSDL describableIn WSDL NOT describable >Operations of interface >Parameters of operations >Structure and types of parameters (XML Schema) >Relations between –Values in SOAP message –Request and response –Several operations Is part of Contract!

3. 3 Describing Relations >Relations expressed in predicate logic >Required: Operations to handle XML! (For expressions about SOAP messages.) >To be described: –SOAP body –SOAP header entries –SOAP error messages (E.g.: When is which returned?) >Description of dynamic behavior –E.g. Allowed order of operation calls –Relation between SOAP message and history (Can be expressed in predicate logic.) –Similar to: Hoare‘s Traces (See: Hoare, C.A.R: Communicating Sequential Processes. Prentice-Hall International, UK, LTD, 1985.) Also relations among each other!

4. 4 Predicate Logic Expressions in WSDL >WSDL + Description of relations = Complete description of contract >Advantage: Contract completely in WSDL document >Extensions allowed in WSDL (as „extensibility elements“) >Predicate logic expressions can be put there >Goals of extended WSDL: –Documentation for developers –Basis for automatic validation und verification

5. 5 >Automatic validation: >To be checked: –Message a valid SOAP message? (Conforming to SOAP standard) –SOAP message conforming to „classic WSDL“? Includes XML Schema validation –Are all predicate logic expressions true? Automatic Validation Validator: Checks for every message, if it conforms to the specification.

6. 6 Verification of Web Services >Formal specification of interface = Basis for verification >To be considered: –Predicate logic expressions –Everything described in WDSL including parts in XML Schema –Implicit things from SOAP standard >Advisable (if possible) : Transformation of WSDL und implicit things into predicate logic expressions. Must not be forgotten!