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Learn about web services development using WSDL (Web Services Description Language) for contracts and RDF (Resource Description Framework) for metadata representation. Understand elements, examples, discussions, and XML mappings. Enhance your skills in service composition, access, and discovery.

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Descriptions

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  1. Descriptions Robert Grimm New York University

  2. The Final Assignment… • Your own application • Discussion board • Think: Paper summaries • Web cam proxy • Think: George Orwell or JenCam • Visitor announcement and tracking • Look at 7th floor lobbies at 715 Broadway

  3. The Final Assignment… (cont.) • Ground rules • Implemented as a web proxy or SOAP service • For SOAP services you need to implement a client as well • Built on top of Munin, uses HTTP/1.1 • A continuation of the semester-long group effort • One paragraph summary due 11/18

  4. The Final Assignment… (cont.) • Due 12/2 before class • In-class talk and live demo • 20 minutes per group • 3 introductory slides • Application overview (what does it do?) • Implementation overview (how does it work?) • Lessons learned (what did you get out of it?)

  5. Descriptions in One Slide • The overall challenge: Provide metadata • How to find services? • How to access services? • How to compose services? • Today’s journey • WSDL as the IDL for web services • RDF as a general description language • OWL as a way to reason about descriptions

  6. WSDL Overview • WSDL provides a contract between clients and services • Functions • Data types • Wire protocol • Address • Naturally, this contract is expressed in XML

  7. WSDL Elements • The five main elements (children of definitions) • types • Complex types • message • Definition of messages • portType • Combination of messages into operations (think request/response) • binding • Description of wire protocol (think SOAP) • service • Address of service (think URL)

  8. WSDL Elements (cont.) • Two utility elements • documentation • Human-readable information • import • Inclusion of other WSDL documents

  9. A WSDL Example • <?xml version="1.0" encoding="UTF-8"?><definitions name="HelloService" targetNamespace="http://www.ecerami.com/wsdl/HelloService.wsdl" xmlns="http://schemas.xmlsoap.org/wsdl/" xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/" xmlns:tns="http://www.ecerami.com/wsdl/HelloService.wsdl" xmlns:xsd="http://www.w3.org/2001/XMLSchema">

  10. A WSDL Example (cont.) • <message name="SayHelloRequest"> <part name="firstName" type="xsd:string"/></message><message name="SayHelloResponse"> <part name="greeting" type="xsd:string"/></message><portType name="Hello_PortType"> <operation name="sayHello"> <input message="tns:SayHelloRequest"/> <output message="tns:SayHelloResponse"/> </operation></portType>

  11. A WSDL Example (cont.) • <binding name="Hello_Binding" type="tns:Hello_PortType"> <soap:binding style="rpc“ transport="http://schemas.xmlsoap.org/soap/http"/> <operation name="sayHello"> <soap:operation soapAction="sayHello"/> <input> <soap:body encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" namespace="urn:examples:helloservice" use="encoded"/> </input> <output> <soap:body encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" namespace="urn:examples:helloservice" use="encoded"/> </output> </operation></binding>

  12. A WSDL Example (cont.) • <service name="Hello_Service"> <documentation>WSDL File for HelloService</documentation> <port binding="tns:Hello_Binding" name="Hello_Port"> <soap:address location="http://localhost:8080/soap/servlet/rpcrouter"/> </port></service></definitions>

  13. WSDL Discussion • Who generates WSDL? • Who generates corresponding code? • Why do we need inclusions? • What is missing? • What service is provided? • Think discovery • When should I use this service? • Geographic limitations, quality, cost • How does the service work?

  14. RDF • A language for representing meta-data • Is more structured than plain XML • Includes its own schema language (RDF-Schema) • Based on a simple (but powerful) model • Statements consist of <subject, predicate, object>or <resource, property, value> • To express ontologies • Powerful combinations • Predicates, objects, and statements can become subjects themselves • Formal semantics

  15. “There is someone, whose name is Eric Miller, whose email is em@w3.org, and whose title is Dr.” An RDF Example

  16. The Corresponding XML Representation • <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:contact="http://www.w3.org/2000/10/swap/pim/contact#"> <contact:Person rdf:about="http://www.w3.org/People/EM/contact#me"> <contact:fullName>Eric Miller</contact:fullName> <contact:mailbox rdf:resource="mailto:em@w3.org"/> <contact:personalTitle>Dr.</contact:personalTitle> </contact:Person></rdf:RDF>

  17. But RDF Is Not Enough • Several successive extensions • DAML (DARPA Agent Markup Language) • OIL (Ontology Inference Layer) • DAML+OIL • OWL (Web Ontology Language) • W3C!!! • Common push • Richer way of restricting and relating classifications

  18. OWL • Three sublanguages • Lite, DL, Full • Simple classification hierarchy • Maximum expressiveness while also providing computational completeness and decidability • “It is unlikely that any reasoning software will be able to support complete reasoning for every feature of OWL Full.” • Features • Basic definitions • Class, property, subclass, subproperty, domain, range • (In)Equality, property characteristics, type restrictions, cardinality restrictions, intersection, versioning,…

  19. The Three Faces of XML • Documents • Plain XML, DTDs • Serialized data • Structured data, XML-Schema • Metadata • RDF, OWL

  20. Discussion • Who writes descriptions? • Who manages evolution of descriptions? • Is there one ontology or many ontologies? • If there are many, how do we map between them? • How do we use descriptions?

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