Web Service Brokerage using Semantic Web Technologies

1. Web Service Brokerage using Semantic Web Technologies By Janaka Liyanage

2. Why Semantics? • WSDL & UDDI based on XML syntax • If the supplier publishes a service to sell “Published Documents” and a user wants to buy “Books” and do a search on “Books” he will not get a hit. No way to define the relationships between terms

3. Semantic Web • Current Web based on syntax (HTML) • The proposed Semantic Web based on semantics (RDF & RDFS & OWL) and is an extension to the current one • Semantic Web out of research labs now

4. Semantic Web • Current Web – for humans • Semantic Web –for computers • Agents – programs that collect Web content from diverse sources, process the information and exchange the results with other programs. • Distributed approach to knowledge representation: URIs used to uniquely identify meanings given to terms and to locate definitions • “Properly designed, the Semantic Web can assist the evolution of human knowledge as a whole”

5. OWL (Ontology Web Language) • RDF based on triples (subject, predicate, object) • RDFS introduces the notion of classes • OWL introduces: • Ontologies (explicit specification of a conceptualization) which are used to organize knowledge (classes and properties) into domains • Logic OWL Classes <owl:Class rdf:ID="Region"/> Definig an instance of a class <Region rdf:ID="Asia"/> Definig a sub class of Region <owl:Class rdf:ID=“Country"> <rdfs:subClassOf rdf:resource="#Region"/> </owl:Class>

6. Classes & Properties <owl:ObjectProperty rdf:ID="locatedIn"> <rdf:type rdf:resource="&owl;TransitiveProperty" /> <rdfs:domain rdf:resource="&owl;Thing" /> <rdfs:range rdf:resource="#Region" /> </owl:ObjectProperty> Everything (including a region itself) located in some region <Region rdf:ID="Sri Lanka"> <locatedIn rdf:resource="#Asia"/> </Region> <Region rdf:ID="Colombo"> <locatedIn rdf:resource="#Sri Lanka"/> </Region> Can infer that Colombo is located in the Asia region

7. Semantic Web Services (SWS) • Designed to overcome the problems with conventional web services, by integrating semantic markup into web services descriptions • Agents being able to make sense of the capabilities and how to invoke these SWS • Two approaches OWL-S and WSMO • OWL-S is the W3C recommended and widely accepted

8. OWL-Services (OWL-S) • A set of OWL ontologies to describe a web service • Service is the central class which represents a SWS • A SWS may correspond to zero or more conventional web services

9. Service Profiles • Describes capabilities, requirements, publisher information, QoS and optionally the category • Describes the inputs, outputs, preconditions and effects (IOPE) of a service. • These details of the service are described using the ServiceProfile class’s properties hasInput, hasOutput, hasPrecondition and hasResult respectively • Allows capability based discovery of web services, rather than keyword based searching as in UDDI

10. Sample IOPEs of Services A process for confirming a reservation of a seat <profile:Profile rdf:ID="ConfirmReservation"> <profile:hasInput rdf:resource="#ReservationID_In"/> <profile:hasInput rdf:resource="#Confirm_In"/> <profile:hasOutput rdf:resource="#SeatNum_Out"/> <profile:hasOutput rdf:resource="#ReservationID_Out"/> <profile:hasEffect rdf:resource="#HaveSeat"/> </profile:Profile> <process:Input rdf:ID="ReservationID_In"> <process:parameterType rdf:resource="&concepts;#ReservationNumber"/> </process:Input> <process:Effect rdf:ID="HaveSeat"> <process:ceEffect rdf:resource="&concepts;#HaveFlightSeat"/> </process:UnConditionalEffect>

11. Service Models • A class called Process, describes how the underling service(s) works • Divides processes into 2 categories • AtomicProcess: corresponds to the actions a service can perform by a single interaction. An AtomicProcess directly executes a single underlying web service, and thus should contain a mandatory instance of ServiceGrounding. • CompositeProcess: is a process which is composed of atomic or other composite processes. A CompositeProcess should define the execution and data flow paths between its constituting processes, using the control constructs: Sequence, Split, Split + Join, Choice, Any-Order, Condition, If-Then-Else, Iterate, Repeat-While, and Repeat-Until.

12. Service Grounding • Tying together a WSDL description and a OWL-S description of a service • So that OWL-S service can be executed • Inputs & outputs of Atomic Processes are mapped to the WSDL message parts • XSL transforms used to convert OWL types to WSDL types

13. Web Service Brokers • An ideal brokerage system should contain • Automatic service discovery • Automatic service composition • Automatic mediation • No current broker with all this functionality • Either implements partial functionality or requires human intervention • E.g. OWLS-MX, XPlan, CMU OWL-S Broker

14. My Brokerage System Three parties of the system A possible composition plan generated by broker Booking a seat to travel COL to NY in the cheapest route Executes four services sequentially and iteratively

15. Architecture • Used Java language • Apache Axis for creating and executing web services • Apache Tomcat server hosts the broker and provider services • Uses Jena API (by HP labs) to manipulate RDF & OWL data • Uses “Pellet” Inference engine for reasoning

16. Implementation • Extended OWL-S specification to suit my requirements • Used RDQL queries to extract information from the knowledge base • Used a tool named WSDL2OWLS to generate skeleton OWL-S descriptions for the services • Used XSL transforms to convert OWL types to SOAP messages and vice versa

17. Implementation Issues • SOAP marshalling for complex types (not standardized) • .NET web services and Java service not compatible – when coming to complex types • Lot of defects in tools and libraries (still in primitive stages) • WSDL2OWLS • had to correct bugs by modifying code • Jena API when processing to OWL • Had to find a workaround

18. Demonstration • Demonstrating only the tip of the iceberg • “TcpTrace” to see the interaction between the provider and services • Uses the flight booking scenario to evaluate the prototype • Get all routes from a source airport to a destination • Get the minimum cost route from a set of routes • Book a seat in a flight route • Get the credit card details of a person given the bank

19. Sample Composite Services • Sequential execution of services • Concurrent execution of services

20. Thank You Any Questions?