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Web Services Basics

Web Services Basics. EECS600 Internet Applications Michael Rabinovich. HTTP + CGI = Web Services?. URLs allow to encode arguments to a program Web servers can specify that a URL invokes an executable Exposes API for the executable to communicate with the Web server

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Web Services Basics

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  1. Web Services Basics EECS600 Internet Applications Michael Rabinovich

  2. HTTP + CGI = Web Services? • URLs allow to encode arguments to a program • Web servers can specify that a URL invokes an executable • Exposes API for the executable to communicate with the Web server • Standard ways to pass arguments from HTTP request to executable • Standard ways to pass results from executable to HTTP response

  3. CGI is not Enough • Hard to pass complex data types as arguments • Hard to use between executables • Involves extensive human interaction • Involves manual integration and ad-hoc implementation of caller

  4. Web Services Main Building Blocks • XML as data format • SOAP as invocation mechanism • WSDL as interface description • UDDI for service discovery • Web applications server • Servlet API (alternative to CGI) • J2EE environment

  5. Why XML?

  6. <H2> Important Dates </H2> Note: all deadlines are firm! <UL> <LI>Abstracts due: January 5, 2004</LI> <LI>Full papers due: January 12, 2004</LI> <LI>Decisions due: March 12, 2004</LI> <LI>Final version due: April 12, 2004</LI> <UL> HTML: Syntactic Tags Tags reflect document structure and appearance <I>Milestones</I> <BR><HR> <TABLE> <TR><TD> Submission deadline</TD> <TD>7.2.04.</TD> </TR> <TR><TD> Decision notification</TD> <TD>7.3.04</TD> </TR> <TR><TD> Camera copy due</TD> <TD>12.5.04</TD></TR> </TABLE> www.acm.org/sigmod.html www.computer.org/icde/cpf.html

  7. XML: Semi-Structured Data <deadlines> <preamble> <H2> Important Dates </H2> Note: all deadlines are firm! </preamble> <interest text=“Abstracts due:”> <date>January 5, 2004 </date> </interest> <submission text=“Full papers due:”> <date>January 12, 2004 <date/> </submission> </deadlines> • Self-expressive tags • Content (can be) separated from appearance • Structural restrictions • Suitable for both humans and applications <deadlines> <preamble> Milestones </preamble> <submission text=“Submission deadline:”> <date>7.2.04<date/> </submission> </deadlines>

  8. deadlines preamble interest submission date date PCDATA PCDATA PCDATA XML Trees <deadlines> <preamble> <H2> Important Dates </H2> Note: all deadlines are firm! </preamble> <interest text=“Abstracts due:”> <date>January 5, 2004 </date> </interest> <submission text=“Full papers due:”> <date>January 12, 2004 <date/> </submission> </deadlines>

  9. XML Namespaces . . . <n:passenger xmlns:n="http://mycompany.example.com/employees"> <n:name>Åke Jógvan Øyvind</n:name> </n:passenger> <c:payment xmlns:c="http://creditcompany.com/credit"> <c:name> <c:employee> Åke Jógvan Øyvind</c:employee> <c:company> Mycompany </c:company> </c:name> </c:payment> . . . • Avoiding tag name conflicts

  10. It’s Easier with XML! • Easier to find documents of interest • Keyword queries as before • Structural queries • Easier to extract data from documents • Easier to reformat and construct new documents • Easier to process document in an application

  11. Typical Web Application Scenario (2) Query for service (Obtain UDDI/WSDL files) (1) Register service (UDDI file, WSDLpointers) Middleware Client Server (3) Use WSDL file to write apps (4) SOAP calls

  12. SOAP • XML dialect for specifying Web service requests and responses • Typically, it is XML encoding for RPC • Typically, it is carried over HTTP (“HTTP Binding”) • Web service is identified by a URL • Node providing service • Resource on the node (e.g., service name) • Additional information in request: • Procedure (method) name • Input parameters • Information in response: • (Responding procedure name) • Output parameters • Return code

  13. SOAP Request POST /Reservations HTTP/1.1 Host: travelcompany.com Content-Type: application/soap+xml; charset="utf-8" Content-Length: nnnn <?xml version='1.0' ?> <env:Envelope xmlns:env="http://www.w3.org/2003/05/soap-envelope" > <env:Header> <t:transaction xmlns:t="http://thirdparty.com/transaction" env:mustUnderstand="true" > 5 </t:transaction> </env:Header> <env:Body> <m:chargeReservation env:encodingStyle="http://www.w3.org/2003/05/soap-encoding" xmlns:m="http://travelcompany.com> <m:reservation <m:code>FT35ZBQ</m:code> </m:reservation> <o:creditCard xmlns:o="http://mycompany.com/financial"> <n:name xmlns:n="http://mycompany.com/employees"> Åke Jógvan Øyvind </n:name> <o:number>123456789099999</o:number> <o:expiration>2005-02</o:expiration> </o:creditCard> </m:chargeReservation> </env:Body> </env:Envelope>

  14. SOAP Response HTTP/1.1 200 OK Content-Type: application/soap+xml; charset="utf-8” Content-Length: nnnn <?xml version='1.0' ?> <env:Envelope xmlns:env="http://www.w3.org/2003/05/soap-envelope" > <env:Header> <t:transaction xmlns:t="http://thirdparty.com/transaction” env:mustUnderstand="true"> 5 </t:transaction> </env:Header> <env:Body> <m:chargeReservationResponse env:encodingStyle="http://www.w3.org/2003/05/soap-encoding" xmlns:rpc="http://www.w3.org/2003/05/soap-rpc" xmlns:m="http://travelcompany.com/"> <rpc:result>m:status</rpc:result> <m:status>confirmed</m:status> <m:code>FT35ZBQ</m:code> <m:viewAt> http://travelcompany.example.org/reservations?code=FT35ZBQ </m:viewAt> </m:chargeReservationResponse> </env:Body> </env:Envelope>

  15. Options • Message exchange patterns • Request-response • Using HTTP POST method • Both request and response are SOAP messages • Response • For idempotent method invocations • Using HTTP GET • Parameters encoded in a URL • Only response is SOAP • HTTP-based request/response matching

  16. WSDL • Supports automation of SOAP programming • Specifies a Web service: • Abstract message interaction scenarios • “Binding” of abstract messages to physical formats • Service end-point (whom to invoke)

  17. WSDL File Sections • Description attributes • Define namespaces • System namespaces (WSDL, SOAP, WSDL Extensions) • Service-specific namespaces • Documentation • Human-readable description • Types • XML schemas of every message • Interface • Lists operations, and for each operation the in/out messages • Binding • Specifies underlying protocol (HTTP), SOAP message exchange pattern, encoding style (message serialization) • Service • Service URL

  18. <?xml version="1.0" encoding="utf-8" ?> <description xmlns="http://www.w3.org/2005/08/wsdl" targetNamespace= "http://greath.example.com/2004/wsdl/resSvc" xmlns:tns= "http://greath.example.com/2004/wsdl/resSvc"> <documentation>This document describes the GreatH Web service. </documentation> <types> <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" targetNamespace="http://greath.example.com/2004/schemas/resSvc" xmlns:ghns ="http://greath.example.com/2004/schemas/resSvc"> <xs:element name="checkAvailability" type="tCheckAvailability"/> <xs:complexType name="tCheckAvailability"> <xs:sequence> <xs:element name="checkInDate" type="xs:date"/> <xs:element name="checkOutDate" type="xs:date"/> <xs:element name="roomType" type="xs:string"/> </xs:sequence> </xs:complexType> <xs:element name="checkAvailabilityResponse" type="xs:double"/> </xs:schema> </types> <interface name = "reservationInterface" > <operation name="opCheckAvailability" pattern="http://www.w3.org/2005/08/wsdl/in-out" style="http://www.w3.org/2005/08/wsdl/style/iri"> <input messageLabel="In" element="ghns:checkAvailability" /> <output messageLabel="Out" element="ghns:checkAvailabilityResponse" /> </operation> </interface> <binding name="reservationSOAPBinding" interface="tns:reservationInterface" type="http://www.w3.org/2005/08/wsdl/soap" wsoap:protocol="http://www.w3.org/2003/05/soap/bindings/HTTP"> <operation ref="tns:opCheckAvailability" wsoap:mep="http://www.w3.org/2003/05/soap/mep/soap-response"/> </binding> <service name="reservationService" interface="tns:reservationInterface"> <endpoint name="reservationEndpoint" binding="tns:reservationSOAPBinding" address ="http://greath.example.com/2004/reservation"/> </service> </description>

  19. UDDI • Registry for Web services • Human readable contact information • Business categorization • WSDL file or file pointer • Itself uses SOAP to interact with registry

  20. Web Services Readings • Web Services Description Language (WSDL) Version 2.0 Part 0: Primer http://www.w3.org/TR/2005/WD-wsdl20-primer-20050803/ • SOAP Version 1.2 Part 0: Primer http://www.w3.org/TR/2003/REC-soap12-part0-20030624/ • OASIS UDDI Specifications http://www.oasis-open.org/committees/uddi-spec/doc/tcspecs.htm

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