Presentation 7: SOAP, WSDL & introduction to UDDI.

Presentation 7:

SOAP, WSDL & introduction to UDDI

Ingeniørhøjskolen i ÅrhusSlide 2 af 51

Outline

• Overview of Web Services & SOAP• Service-Oriented Architecture

– Service Description– Service Registration and Discovery– Service Execution

• Emerging Web Services standards:

SOAP, WSDL, UDDI (introduced)

Web Service Defined

• W3C definition:– [Definition: A Web service is a software system

designed to support interoperable machine-to-machine interaction over a network. It has an interface described in a machine-processable format (specifically WSDL). Other systems interact with the Web service in a manner prescribed by its description using SOAP messages, typically conveyed using HTTP with an XML serialization in conjunction with other Web-related standards.]

Overview SOAP & Web services

• SOAP – Simple Object Access Protocol - & Web services:

– A light-weight & ultra heterogenic alternative to CORBA, DCOM & RMI

– Openness in focus – meant for opening legacy applications for others

– Not meant in the role of Inter business, large scale, transaction heavy communication (as CORBA & J2EE)

– But can prob. be used for it!– Does not have services for transactions,

concurrency, persistence, scalability– Does have discovery services (UDDI) giving

some degree of location transparency– Does have Interface Definition Language for

heterogeneity (WSDL)– Fails on several of the dist. system

requirements!– But easy to implement yourself!

Why SOAP When We Have CORBA?

• CORBA has been considered too complex by many– May not be true with new development tools using wizards

• They aim at solving different tasks:– SOAP covers light-weight application integration within the

enterprise, exposing legacy business objects across enterprises, and sharing resources (like Google Search Engine, or Sonofon SMS/MMS API) on the net, as well as technology openness

– CORBA has a wide range of services for (as we shall see later):• Locating, creating & moving objects• Object relationship management between hosts• Persistency services – activation frameworks etc.• Distributed concurrency and transaction management • Security

– Only some are supported in SOAP tech family – its lightweight– Lesson: define your needs – and find the right technology

Regarding SOAP• SOAP is not by it self revolutionary – its merely:

– a framework for exchanging XML-based information in a network (via protocols of the TCP/IP family) – with RPC capabilities

– the currently most hyped XML / Web service technology • But when combined with other technologies like

– WSDL &– UDDI – It solves several of the requirements of a Distributed System

• And the fact that it is an open standard – supported by all major software vendors and programming languages:– C++– Java– C#– Delphi– Visual Basic and many more

• Makes it somewhat revolutionary! A practical solution – like WWW

Examples of Web Services

• Google's Web Service - access the Google search engine – http://www.google.com/apis/

• Amazon's Web Service - access Amazon's product information – http://associates.amazon.com/exec/panama/associates/join/

developer/resources.html

• XMethods - collection of information about existing Web services – http://www.xmethods.com

• SalCentral - WSDL / SOAP Web services search-engine – http://www.salcentral.com/salnet/webserviceswsdl.asp

Google Web Service

Service-Oriented Architecture (SOA)

ClientClientServerServer

RegistryRegistryAbstract Architecture- Web service stackAbstract Architecture- Web service stack

Legacycode onserver

Opening up for doing business (the sharing of objects) on the Internet

Technologies for Implementing SOA

SOAP for communicationSOAP for communication WSDL for contract & bindingWSDL for contract & binding

UDDI & WSDL for registration & discoveryUDDI & WSDL for registration & discovery

SOAP is used for Client/Server communications

What is SOAP?

• Simple Object Access Protocol• Wire protocol similar to

– IIOP for CORBA– JRMP for RMI

• XML is used for data encoding – “text” based protocol vs. “binary” protocol

• Supports XML-based RPC

What is Not SOAP?

• Not a component model– So it will not replace objects and components, i.e. EJB,

JavaBeans and .NET

• Not a programming language– So it will not replace Java, C# og C++

• Not a solution for all– So it will not replace other distributed computing

technologies such as RMI and CORBA

Where is SOAP?

• W3C XML Protocol working group– SOAP 1.2 current version:

http://www.w3.org/TR/soap12/

• Microsoft, SUN, Oracle, HP, IBM all support the W3C recommendation– but there are still differences to be overcome– security issues, transactions etc.

What does SOAP define?

• Message Envelope• Encoding Rules• RPC Convention• Binding with underlying protocols

– HTTP (which we will use in this course)– SMTP– FTP and others

SOAP Message Format

Possible to Attach binaries (images, cryptographic material) to attachmentsPossible to Attach binaries (images, cryptographic material) to attachments

SOAP Message Envelope

• Encoding information• Header

– Optional– Could contain context knowledge

• Security• Transaction

• Body– RPC methods and parameters– Contains application data

Two types of communication

SOAP RPC Request Example

<SOAP-ENV:Envelope

xmlns:SOAP-ENV="…"

SOAP-ENV:encodingStyle="…">

<SOAP-ENV:Header>

</SOAP-ENV:Header>

<SOAP-ENV:Body>

<m:GetLastTradePrice xmlns:m=“some_URI">

</m:GetLastTradePrice>

</SOAP-ENV:Body>

</SOAP-ENV:Envelope>

SOAP RPC Response Example

<SOAP-ENV:Envelopexmlns:SOAP-ENV="…"SOAP-ENV:encodingStyle="…"><SOAP-ENV:Header>

</SOAP-ENV:Header><SOAP-ENV:Body>

<m:GetLastTradePriceResponse xmlns:m=“some_URI"><price>30.5</price>

</m:GetLastTradePriceResponse></SOAP-ENV:Body>

</SOAP-ENV:Envelope>

SOAP RPC composition I

• Information needed for a method call:1. The URI of the target object (marked with red)

• <SOAP-ENV:Body><m:GetLastTradePrice xmlns:m=“http://stocks.com/StockQuotes">

</SOAP-ENV:Body>

SOAP RPC composition II

• Information needed for a method call:1. The URI of the target object

2. The Method Name

<SOAP-ENV:Body>

<m:GetLastTradePrice xmlns:m=“http://stocks.com/StockQuotes">

</SOAP-ENV:Body>

SOAP RPC composition III

• Information needed for a method call:1. The URI of the target object

2. The Method Name

3. Parameters

4. Binding protocol (next slide)

<SOAP-ENV:Body>

<m:GetLastTradePrice xmlns:m=“http://stocks.com/StockQuotes">

</SOAP-ENV:Body>

Name is not important

SOAP RPC composition IV: complete SOAP RPC Request

POST /StockQuote HTTP/1.1Host: www.stockquoteserver.comContent-Type: text/xml; charset="utf-8"Content-Length: nnnnSOAPAction: "Some-URI"

<SOAP-ENV:Envelope xmlns:SOAP-ENV=”http://schemas.xmlsoap.org/soap/encoding" SOAP-ENV:encodingStyle=”http://schemas.xmlsoap.org/soap/envelope/">

<SOAP-ENV:Body><m:GetLastTradePrice xmlns:m=" http://stocks.com/StockQuotes">

</SOAP-ENV:Body></SOAP-ENV:Envelope>

HTTPHTTP

EncodingEncoding

Name-spaceName-space

STEP 4: BINDING TO PROTOCOLSTEP 4: BINDING TO PROTOCOL

Request to HelloWorld.jws

Input parameters type stringInput parameters type string

HTTP Post CallHTTP Post Call

HTTP Host TargetHTTP Host Target

Method nameMethod name

… and the HTTP Response from Server

HTTP ResponseHTTP Response

Method ResponseMethod Response

Parameter valueParameter valueParameter nameParameter name

Apache Tomcat Server RespondingApache Tomcat Server Responding

In addition

• There is:– Response handling– Fault handling

Lucky us

• Luckly we dont have to understand SOAP– So it does not really matter that it is somewhat complex– Unless we want to develop clients that do not have a

SOAP API– ... But then we need an XML parser … and more …– BUT IT IS POSSIBLE and might be feasible

How to make a Web service with SOAP

• You need an application or API capable of supporting:– Communication over the Internet (HTTP)– Security (SSL)– XML Parsing capabilities– …

• Two examples of Application Servers with support:– Apache Tomcat Application Server with AXIS– Microsoft Internet Information Server

• JAX-RPC (JSR-101)– Java™ API for XML-based RPC– Need to implement features manually

Issues with SOAP

• Issues with SOAP– Lack of business semantics– Insufficient functionality for business operations– Security– Reliability– Under development

• Low performance

• WSDL is used for describing WebServices

What is WSDL?

• XML language for describing web services• Web service is described as

– A set of communication endpoints (ports)

• Endpoint is made of– Abstract definitions of operations and messages– Concrete binding to networking protocol and message

format

Why WSDL?

• Enables automation of communication details between communicating partners– Machines can read WSDL– Machines can invoke a service defined in WSDL

• Note that WSDL defines only low-level aspects of Web services, however other technologies might follow …– Security– Transactions– Persistency

WSDL Document Example

• Simple service providing stock quotes• A single operation called GetLastTradePrice• Deployed using SOAP 1.1 over HTTP• Request takes a ticker symbol of type string• Response returns price as a float

WSDL Elements

• Types– Data type definitions– Used to describe exchanged messages– Uses W3C XML Schema as canonical type system

WSDL Example: Types

WSDL Elements

• Messages– Abstract, typed definitions of data being exchanged

• Operations– Abstract description of an action– Refers to input and output messages

• Port type– Collection of operations – Resembles a Class in OOPL

Example:Messages, Operation, Port type

WSDL Elements

• Binding– Concrete protocol and data format for a particular Port

type– Example: SOAP 1.1, HTTP, MIME

• Port– Defines a single communication endpoint– Address for binding– URL for HTTP, email address for SMTP

• Service– Aggregate set of related ports

WSDL Elements

HelloWorld.jws?wsdl

• Generate WSDL document from– existing Java classes or EJB components– AXIS: Java2WSDL

• Generate SOAP messages from– WSDL document (via client stub and server skeleton)

• JAX-RPC, Forte for Java, JBuilder, JDeveloper

• UDDI for publishing & discovery – the SOA

• Universel Descrition, Discovery & Integration• UDDI defines a scheme to publish and discover

information about Webservices• Programmatic registration and discovery business

entities and their Webservices• Based on SOAP, HTTP, XML• Registry data

– Business registrations– Service type definitions

Registration

• “ White pages”– Address, contact, and known identifiers

• “ Yellow pages”– industrial categorizations– Industry: NAICS (Industry codes - US Govt.)– Product/Services: UN/SPSC (ECMA)– Location: Geographical taxonomy

• “ Green pages”– technical information about services

What uses UDDI?

• Tool building client (Service Consumer)– Browse or search registry– Create a service proxy

• Tool publishing the service– Generates WSDL– Construct UDDI entries

• Application that needs dynamic binding– Directly access UDDI– Query can be pre-generated

SOAP & Web Services in relation to Distributed Objects

SOAP and Distributed Objects

• SOAP in it self has nothing to do with objects• There probably is SOAP API’s for C and COBOL• The trick is the supporting API’s converting

objects to WSDL and SOAP for serialization across the network

• Using the Proxy Pattern for decoupling – perhaps with the Façade Pattern for larger granularity– Emmerich: Accessing distributed objects is expensive– Use larger granularity

• More on Architecture later in the course

Proxy Pattern (GoF version)

WatchClient

RealWatchProxyWatch TestWatch

setTime()

setTime() setTime() setTime()

Objects of RealWatch class are locateed on a different machinethan the Client object.This is an example of Remote Proxy – which is anArchitectural Pattern. from GoF

abstract

GoF: Gang Of Four (Design Pattern bog af Gamma m.fl.)

Proxy Pattern (B. Douglas version)

ClientObject

SOAPProxy

Serverobject

BD.s212

Client component

Server component

Proxy Pattern Client

Server Proxy

Proxy (= en stedfortræder)

By encapsulatingThe SOAP communicationin a Proxy,we have decoupled theClient Object fromneeding to knowthat it calls overThe Internet. Thus making it easyto implementdifferent Middlewareand use the Serverobject locallyWe could do the same for

The Server object

Façade Pattern (also GoF)

Used for encapsulation and decouplingUsed for encapsulation and decoupling

The entire Client Subsystem is decoupled from the serverand a Client Proxy hides the SOAP implementation (also Server Proxy)

This is known as Client Stubs & Server Skeletons

The entire Client Subsystem is decoupled from the serverand a Client Proxy hides the SOAP implementation (also Server Proxy)

This is known as Client Stubs & Server Skeletons

Presentation 7: SOAP, WSDL & introduction to UDDI.

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