 Copyright 2006 Digital Enterprise Research Institute. All rights reserved. Web Services eXecution Environment (WSMX) (A ‘What not the How’ Approach to Distributed Computing) Matthew Moran Digital Enterprise Research Institute National University of Ireland, Galway

2 Contents Introduction Conceptual model Mediation Discovery Reference architecture Summary

3 Aiming for Seamless B2B Integration at Web Scale Buy 100 IBM R50p power supplies Data: UNSPSC B2B Protocol: ebXML Data: RosettaNet B2B Protocol: RosettaNet Data : EDI B2B Protocol: EDI Ship to Africa Service Client

4 RPC based Distributed Computing Network layer Wire protocol Client stubServer stub Client Server

5 CORBA and DCOM build on RPC Object oriented distributed computing – RMI –Objects in one process invoking objects in another process Typed interfaces defined using IDL –Build-time type checking Standardised bindings to programming languages –Java, C, C++, Lisp, Python, Smalltalk At least 15 years of research into –Efficiency, transactionality, reliability, exception handling

6 The Promise of Web Services web-based SOA as new system design paradigm

7 Web services a step back scientifically Re-inventing inferior technology –No standardised mappings to programming languages –Not type-safe –Immature notions of security, transactionality, reliability –Closer to RPC – no polymorphism or inheritance But there are advantages … –Language and platform independent –Web standard specifications: URIs, XML, HTTP –Open and interoperable – scale for the Web

8 Current Situation Web services descriptions are structural only –WSDL, UDDI, XML-Schema, BPEL, WS-* Assumption of shared understanding of semantics –Data, process, protocol, policy, QoS Web service usability, usage, and integration needs to be inspected manually Design-time binding of services and requesters

9 Adding formal semantics, we can improve … Discovery –How can a machine interpret a textual UDDI description Handling mismatches –Data, process and protocol Composing services –(Semi-) automatically Orchestration –Execution of complex services defined using Workflow

10 Contents Introduction Conceptual model Mediation Discovery Reference architecture Summary

11 WWW URI, HTML, HTTP Semantic Web RDF, RDF(S), OWL Dynamic Web Services UDDI, WSDL, SOAP Static Semantic Web Services The Vision Time

12 Conceptual model for Semantic Web Services Formally describe required knowledge base What a service requester wants to achieve Describe services including the capability they offer and the public interface they provide Overcome interoperability issues for data, process, protocol

13 Conceptual model for Semantic Web Services Formally describe required knowledge base What a service requester wants to achieve Describe services including the capability they offer and the public interface they provide Overcome interoperability issues for data, process, protocol

14 Conceptual model for Semantic Web Services Formally describe required knowledge base What a service requester wants to achieve Describe services including the capability they offer and the public interface they provide Overcome interoperability issues for data, process, protocol

15 Conceptual model for Semantic Web Services Formally describe required knowledge base What a service requester wants to achieve Describe services including the capability they offer and the public interface they provide Overcome interoperability issues for data, process, protocol

16 Contents Introduction Conceptual model Mediation Discovery Reference architecture Summary

17 WSMO Mediator uses a Mediation Service via Source Component Source Component Target Component 1.. n 1 Mediation Services - as a Goal - directly - optionally incl. Mediation Mediator structure

18 Mediation – background theory Ontology alignment with machine assistance building on –Schema-mapping approach of DB integration –Ontology-mapping (MAFRA) and ontology merging (PROMPT) Extended with –With different matching perspectives on ontologies Helps for different types of matches and expertise levels –Top-down and bottom-up approach Caters for different scope for ontology alignment Better guidance during mapping

19 Mediation – background theory Formal model for mapping creation –Abstract model for flexible grounding to ontology langauge –ISWC 2006 paper (building on ontology alignment & merging) Design-time tool –Model is mapped to the graphical elements Run-time –Abstract mappings are grounded to WSML –Automatic execution with WSMX

20 Data mediation in WSMX

21 Example: mapping with top-down decomposition concept ticket type impliesType _string departure_city impliesType _string departure_code impliesType _string arrival_city impliesType _string arrival_code impliesType _string departure_date impliesType date arrival_date impliesType date departure_time impliesType time arrival_time impliesType time issuing_terms impliesType terms firstName impliesType _string lastName impliesType _string concept travelVoucher type impliesType _string bearer impliesType name toFrom impliesType tripPoints departureDate impliesType date … concept tripPoints departure impliesType station arrival impliesType station concept station city impliesType _string stationCode impliesType _string ticket[arrival_city]  travelVoucher[toFrom[arrival[city]]]

22 Contents Introduction Conceptual model Mediation Discovery Reference architecture Summary

23 Discovery Two aspects –Finding the services on the Web –Matching goals with capability descriptions of available services We focus on the matching –What needs to be modelled to make the semantic match –What kind of middleware is needed –What algorithms can we use Finding services on the Web –Subset of problem for Semantic Web Search Engines

24 Matt Objective: „book a flight and a hotel for me for the ICWS 2005.“ Service Registry SWS Discovery has searches VTA result set includes Goal definition Web service discovery

25 Underlying principle State-based formalization of services and goals –Precondition, assumptions, postconditions and effects Follow description logics approach of OWL-S But stick with more intuitive semantics –Postconditions, effects represent ‘objects’ the service can deliver –Preconditions and assumptions represent a ‘contract’ that needs to be fulfilled before discovery can take place Use reasoner to query over combined knowledge base (capabilities, inputs, additional axioms) to get matches

26 Additional axioms may be used

27 Using contracting interface to get additional info Contracting Interface WS1 Contracting Interface WS2 WSMO Registry Discovery Possible Matches Network Goal Collection of WS Step 2 Step 3 Step 1 Step 4

28 Contents Introduction Conceptual model Mediation Discovery Reference architecture Summary

29 WSMX Architecture Execution environment for goal-based invocation of Web services Semantic overlay for Web service-based distributed computing WSMX interprets a client’s goal to –Discover matching service (simple or composed) –Select the best service –Mediate interoperabilities (data, process, protocol) –Enact the interoperation between the client and service Based on the conceptual model provided by WSMO Layered on top of Web service specifications (WSDL, XML, SOAP)

30 WSMX Design Principles Strong decoupling & Strong mediation autonomous components with mediators for interoperability Goal-driven invocation distinguish interface (= description) from implementation (=program) +

31 Architecture overview

32 Reasoner Mins –Datalog + Negation + Function Symbols Reasoner Engine –Features Built-in predicates Function symbols Stratified negation WSML2Reasoner –Reasoning API mapping from WSML to a vendor-neutral rule representation –Contains: Common API for WSML Reasoners Transformations of WSML to tool-specific input data (query answering or instance retrieval) WSML-DL-Reasoner –Features: T-Box reasoning (provided by FaCT++) Querying for all concepts Querying for the equivalents, for the children, for the descendants, for the parents and for all ancestors of a given concept Testing the satisfiability of a given concept with respect to the knowledge base Subsumption test of two concepts with respect to the knowledge base Wrapper of WSML-DL to the XML syntax of DL used in the DIG interface

33 OASIS Semantic Execution Environment (SEE TC) –Based on WSMX architecture –Co-chaired by DERI –EU, US, Asia co-operation W3C member submission –WSMO, WSML and WSMX Standardization

34 WSMX – Summary Current WS technology insufficient for eCommerce –Syntactic nature of WSDL, UDDI, XML Schema … WSMO provides rich formal descriptions –Layering on WSDL and XML Schema for compatibility WSMX: reference implementation for WSMO –Discovery, mediation, choreography, orchestration, enactment of WS Adopted platform for multiple EU Projects (DIP, SUPER, TripCom, SWING, ++) Standardization through OASIS (and input to W3C)