Web Services – Introduction Jens Greive Ayman Tarakji

Web Services – Introduction

Jens Greive Ayman Tarakji

Web Services Introduction | 13.06.2007 | Folie 2Regionales Rechenzentrum für Niedersachsen

Outline

Web Service introductionService Oriented ArchitecturePractical examplesBasic of Extensible Markup Language (XML)

DTDSchema

UDDI – Publishing Web ServicesWSDL – A formal language to describe Web ServicesSOAP – Accessing Web ServicesExample from www.xmethods.comSome challenges of the Web Service Technologie


Web Services – A Description

„ Web service is a piece of software, which provide functionality as blackbox, available on server, accessible via a simple object access protocol and has a well-defined interface“ An example is Google without browser .


Why Web Services?

Transactional web is desired

Convert applications into web applications

Interaction between different systems is needed

Web services can perform functions which can be anything from a simple request to a complicated business process (weather reports, Amazon, etc)

Web services are self-contained and self-describing

Using a service-oriented architecture to provide business services accessed by other applications


SOA – Service Oriented Architecture (1)

Provider– Implements and publishes a web service (WSDL)– Provides the service to customers (SOAP)

Broker– Holds a list of published web services (UDDI)– Provides a dynamic search functionality for requesters (UDDI)

Requester– Searches for a specific web service in the broker's list (WSDL)– Establishes a connection with the provider and uses the service (SOAP)

Requester Broker

Provider

Find

Bind Publish

WSDL

UDDI

WSDLSOAP


Web Services (Examples)

Book a flightSouth West Airline connects its own booking system with the one of Dollar Car Rentals

using Dollar Car's Web ServiceA customer booking a flight over the South West homepage can book a car together

with the flight without leaving the South West website

Restaurant guide for PDAsMakes suggestions of restaurants for a user based on the user's profileCalls the Web Service of www.mapquest.com to provide directions to the restaurants


Web Service - Requirements

A mechanism to allow document transfer

Possibility to make Remote Procedure Calls (RPCs)

An easy protocol

Platform independency

Ability to be processed by common programming languages

A formal, standardized language to allow communication between the different roles

Regionales Rechenzentrum für Niedersachsen

XML – Extensible Markup Language

Unlike HTML, XML is used to describe data and not to display it

Currently the lingua franca of information and data encoding

Cross-platform, soft- and hardware independent tool for exchanging information

A meta language for creating xml-based mark-up languages (SGML)

Classification of XML languagesData oriented languages (database systems)Document oriented languages (WML)Protocols and programming languages (XSD, XSLT, WSDL , etc.)Hybrids (data and document oriented)


XML namespaces

Using URIs to identify different name spacesThe cheapest way of getting unique names and avoiding confusions.

<widget type=“gadget“> <head size=“medium“/> <info> <head> <title> description

of gadget </title> </head> <body> … </body> </info></widget>

<widget type=“gadget“ xmlns=“http://www.widget.inc“>

<head size=“medium“/> <info

xmlns:xhtml=“http://www.w3....“> <xhtml:head> <xhtml:title>

description of gadget </xhtml:title> </xhtml:head> <xhtml:body>

… </xhtml:body> </info></widget>


XML syntax

Syntax: very simple and very strict (well-formed)each document has a root element, which in turn has child elements

Land

Forrest Meadow

Tree Tree Tree

<LAND> <FOREST> <TREE>Oak</TREE> <TREE>Pine</TREE> <TREE>Maple </TREE> </FOREST> <MEADOW> <GRASS>Bluegrass</GRASS> <GRASS>Fescue</GRASS> <GRASS>Rye</GRASS> </MEADOW> </LAND


XML syntax: DTD (Data Type Definition)

A schema language for defining the grammar and restrictions over data for the XML document

Basic declaration forms in example:

<!DOCTYPE land SYSTEM “http://www.nature.dk/land.dtd”><!ELEMENT land (forest, meadow)><!ELEMENT forest (tree*)><!ELEMENT meadow (#PCDATA)>

<?xml version=1.1”?><!DOCTYPE land SYSTEM=“http://.../land.dtd>

<land> <forest> <tree>. . . </tree> <tree>. . . </tree> </forest></land>

<?xml version=1.1”?><!DOCTYPE land SYSTEM=”http://.../land.dtd

<land> <meadow> <tree>. . .</tree> <tree>. . . </tree> </meadow></land>

Valid Not Valid


XML syntax: DTD (Data Type Definition)

Pros A simple schema language with a restricted expressive power

Cons character data limitation limited reusability no namespaces supported not self describable not scalable


XML syntax: XSD (XML Schema Definition)

One of the key komponents of XML Overcome DTD limitations (more expressive, self describing and

namespaces supporting)

Inspired from object-oriented programming languages (reuse&comprehensibility) Global as well as local declarations Modularization Nil values in Elements annotations(human readable documentation) subsumption and substitution(xsi:type attribute)

The most central constructs in XSD:1. Simple type definition2. Complex type definition3. Element declaration4. Attribute declaration


XSD - Example

<schema xmlns=“http://www.w3.org/2001/XMLSchema” xmlns:b=“http://businesscard.org targetNamespace=“http://businesscard.org”>

<element name=“card” type=“b:card_type”/><element name=“name” type=“string”/><element name=“phone” type=“string”/><element name=“logo” type=“b:logo_type”/><attribute name=“uri” type=“anyURI”><complexType name=“card_type”> <sequence>

< element ref=“b:name”/> < element ref=“b:phone” minoccurs=“0”/> < element ref=“b:logo” minoccurs=“0”/></sequence>

</complexType><complexType name=“logo_type”> <attribute ref=“b:uri” use=“required”/></complexType>

<schema>


XML Schema (1)

Pros More expressive than DTD Self described Namespace support Written in XML Reusable & comprehensibility More flexible

Cons Too complicated and hard to use (Type mechanism) Context insensitivity – typical problem in XML languages Difficult to enforce a particular root element


XML Schema (2)

Common approach to overcome these problems(guidelines)Example:guildlines of „Danish ministry of science“

Always employ namespaces Use global definitions Reuse existing definitions whenever possible Don´t use the list construct Avoid substitution groups Don´t use unqualified local elements

and many more.


UDDI – Universal Description Discovery and Integration

Requester

Broker

Provider

Find

BindPublish

WSDL

UDDI

WSDLSOAP


UDDI – Universal Description Discovery and Integration

UDDI is an XML-based, platform-independent registry allows businesses worldwide to publish their services and find usefull services

provided by other companiesA UDDI can be thought of as a DNS for business applicationshas a SOAP interface

Two main goals for service discoverySupport developers in finding information about services, so they know how to write

clients which can interact with those servicesEnable dynamic binding by allowing clients to query the registry and obtain references

to services of interest

An UDDI business registration consists of three componentsWhite Pages – Basic information like name, address, unique identifierYellow Pages – Categorizes the registered businessesGreen Pages – Technical information describing the provided services and how they

can be invoked


UDDI – Data types

<businessEntity>

• Name, contact, description

• Identifier and category

<publisherAssertion>

• Connection between two companies

<businessService>

• Grouping of logical services

<bindingTemplate>

• Technical information of a single Web Service

• URL-Accesspoint for this Service

<tModel>

• Specification implemented by the Web Service

• Links pointing to the specifications


WSDL

RequesterBroker

Provider

Find

Bind

Publish

WSDL

UDDI

WSDL

SOAP


WSDL

WSDL WSDL is a platform-, protocol and programming language independent XML-

Specification to describe Web Services Is a Meta language Describes the provided functions, data and types

A WSDL document contains information about the provided interface the protocol which must be used how the service can be accessed

The document does not contain information about Quality-of-Service-Information Taxonomy/Ontology for semantic description of the service


WSDL – Description elements

DatatypesDefinition of the datatypes, which are used to exchange the message

MessageAn abstract definition of the transported data

Port typesDefine the operations so that the Web Service knows how to interpret the data and

what kind of data has to be returned4 different types of exchanged messages

One-way: The service receives an input message from the clientRequest-Response: The service receives an input message from the client and sends an

answerSolicit-response: The service sends a message to the client and waits for a responseNotification: The service sends an output message

BindingDefines the concrete protocol for every port type

PortsDefines an address for the binding. Usually an URI

Service Identifies a Web Service


WSDL – An example (1)

Book price at Barnes & Nobles by ISBN

<wsdl:types><s:schema elementFormDefault="qualified" targetNamespace="http://www.abundanttech.com/webservices/BNPrice"><s:element name="GetBNQuote">

<s:complexType><s:sequence>

<s:element minOccurs="0" maxOccurs="1" name="sISBN" type="s:string"/>

</s:sequence></s:complexType>

</s:element><s:element name="GetBNQuoteResponse">

<s:complexType><s:sequence>

<s:element minOccurs="0" maxOccurs="1" name="GetBNQuoteResult" type="s:string"/>

</s:sequence></s:complexType>

</s:element><s:element name="string" nillable="true" type="s:string"/></s:schema></wsdl:types>


WSDL – An Example (2)

<wsdl:message name="GetBNQuoteSoapIn"><wsdl:part name="parameters" element="tns:GetBNQuote"/>

</wsdl:message><wsdl:message name="GetBNQuoteSoapOut">

<wsdl:part name="parameters" element="tns:GetBNQuoteResponse"/></wsdl:message>

<wsdl:portType name="BNPriceWSSoap"><wsdl:operation name="GetBNQuote">

<wsdl:input message="tns:GetBNQuoteSoapIn"/><wsdl:output message="tns:GetBNQuoteSoapOut"/>

</wsdl:operation></wsdl:portType>

<wsdl:binding name="BNPriceWSSoap" type="tns:BNPriceWSSoap"><soap:binding transport="http://schemas.xmlsoap.org/soap/http”/>

<wsdl:operation name="GetBNQuote"><soap:operation

soapAction="http://.../GetBNQuote" /><wsdl:input>

<soap:body use="literal"/></wsdl:input><wsdl:output>

<soap:body use="literal"/></wsdl:output>

</wsdl:operation></wsdl:binding>


WSDL – An Example (3)

<wsdl:service name="BNPriceWS"><wsdl:port name="BNPriceWSSoap"

binding="tns:BNPriceWSSoap"><soap:address location="http://.../bnprice/bnprice.asmx"/>

</wsdl:port><wsdl:port name="BNPriceWSHttpGet"

binding="tns:BNPriceWSHttpGet"><http:address location="http://.../bnprice/bnprice.asmx"/>

</wsdl:port><wsdl:port name="BNPriceWSHttpPost"

binding="tns:BNPriceWSHttpPost"><http:address location="http://.../bnprice/bnprice.asmx"/>

</wsdl:port></wsdl:service>


WSDL

ProsIndependency between client and serverProgramming language independentPlenty of tools available for processing WSDL documents (code generators like

wsdl2java)

ConsOverhead because of XML


SOAP

Requester Broker

Provider

Find

Bind Publish

WSDL

UDDI

WSDLSOAP


SOAP – Simple Object Access Protocol (1)

Is not simpleSince version 1.2 the abbreviation is no longer used as an acronym because SOAP

is not simple and has nothing to do with accessing objects

Is a framework Sets no rules about the data which should be sentAny application specific data can be transportedSOAP provides a ruleset to define how the XML-Document must look like

Based on existing technologiesXML to describe the data Internet protocols to transport the dataCommon combination is SOAP over HTTP and TCP

Network protocol which allows transfer of documents between systems to call procedures on remote systems (Remote Procedure Calls, RPCs)


SOAP – Simple Object Access Protocol (2)

A SOAP message consists of An SOAP-Envelope, the root element An optional SOAP-Header with processing instructions The SOAP-Body containing the data

SOAP in the TCP/IP Protocol stack

ApplicationSOAP

Transport

Network

HTTP HTTPS ...

TCP

IP


XML to SOAP

<?xml version=‘1.0’ encoding=‘UTF-8’ ?> <SOAP-ENV:Envelope

xmlns:SOAP-ENV=‘http://schemas.xmlsoap.org/soap/envelope/’xmlns:xsi=‚http://www.w3.org/1999/XMLSchema-instance‘xmlns:xsd=‚http://www.w3.org/1999/XMLSchema‘>

<SOAP-ENV:Header>…

</SOAP-ENV:Header> <SOAP-ENV:Body> <PurchaseOrder xmlns=„urn:oreilly-jaws-samples“><shipTo country=„US“>

<name>Joe Smith</name><street>14 Oak Park</street>…

</shipTo><items>

<item>…</item></items>

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

Eigentliches XML-Dokument


SOAP – Remote Procedure Call

Call of a service which returns the price of a book at Barnes & Nobles by a given ISBN:

<?xml version="1.0" encoding="utf-8"?> <soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"><soap:Body>

<GetBNQuote xmlns="http://www.abundanttech.com/webservices/BNPrice"> <sISBN>0130449687</sISBN>

</GetBNQuote>

</soap:Body></soap:Envelope>

<?xml version="1.0" encoding="utf-8"?> <soap:Envelope xmlns:soap="http://.../soap/envelope/">

<soap:Body> <GetBNQuoteResponse xmlns="http://.../BNPrice">

<GetBNQuoteResult>49.99</GetBNQuoteResult> </GetBNQuoteResponse>

</soap:Body> </soap:Envelope>

Response:

http://www.abundanttech.com/webservices/bnprice/bnprice.asmx


SOAP

ProsAllows the use of different transport protocols (HTTP, FTP, etc.)HTTP makes communication behind proxies and firewalls easierXML is simple to parse and widely spreadEasy interaction with a lot of programming languages

ConsUsing XML in SOAP leads to more overhead and slower trafficMany SOAP implementations limit the amount of exchanged data


Using a Web Service – Step 1

www.xmethods.com


Using a Web Service – Step 2


Challenges

Integrating the semantic web specification into Web Services (semantic web annotations group)

Getting Web Services to the point that they can be found and used by applications without human interactionBased on XML WSDL and SOAP are machine readable and processable

More security in Web Services

Delivering a suitable Web Service for the user‘s need (ranking problem)


Summary

Web ServicesSOAXMLUDDIWSDLSOAPExamplesChallenges


Sources

XMLAn introduction to xml and web technologies; Anders Miller, Michael I.

Schwartzbach; Addison Wesley; (Link)http://www.comptechdoc.org/independent/web/xml/guide/http://webservices.xml.com/index.csphttp://www.developer.com/http://www.ibm.com/us/http://www.w3schools.com

Web ServicesJava Web Services; David A. Chappell, Tyler Jewell; O‘Reilly; (Link)http://www.w3.org/2002/ws/http://www.xmethods.com

Some more intresting linkshttp://www.soapclient.com/uddisearch.htmlhttp://www.amazon.com/gp/browse.html?node=3435361http://code.google.com/

Documents

Web Services – Introduction Jens Greive Ayman Tarakji