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– Standard ways to pass arguments from HTTP

request to executable– Standard ways to pass results from executable to

HTTP response

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

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

Why XML?

HTML: Syntactic Tags

<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>

Tags reflect document structure and appearance

<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>

www.acm.org/sigmod.html www.computer.org/icde/cpf.html

XML: Semi-Structured Data

• Self-expressive tags• Content (can be) separated from appearance • Structural restrictions• Suitable for both humans and applications

<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>

<deadlines> <preamble> Milestones </preamble> <submission text=“Submission deadline:”> <date>7.2.04<date/> </submission></deadlines>

XML Trees

deadlines

preamble

PCDATA

submissioninterest

date date

PCDATAPCDATA

<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>

XML Namespaces• Avoiding tag name conflicts . . .

<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> . . .

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

Typical Web Application Scenario

Client

Middleware

Server

(1) Register service(UDDI file, WSDLpointers)

(2) Query for service

(Obtain UDDI/WSDL files)

(3) Use WSDL file to write apps

(4) SOAP calls

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

SOAP RequestPOST /Reservations HTTP/1.1Host: travelcompany.comContent-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>

SOAP ResponseHTTP/1.1 200 OKContent-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>

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

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)

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

<?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>

UDDI

• Registry for Web services– Human readable contact information– Business categorization– WSDL file or file pointer

• Itself uses SOAP to interact with registry

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