Web Services

1
Web Services

• Kaarthik Sivashanmugam
• Department of Computer Science
• The University of Georgia

2
Preface

• I assume
• you all know that this is just an introductory
  session to web services
• you all know XML
• you will ask questions
• we all will enjoy this session

3
Purpose of this session

• Introduction to
• web services
• enabling technologies SOAP, WSDL, UDDI etc
• Understanding
• need for web services
• web services jargons
• Foresee challenges
• Discuss my work

4
What are Web Services ?

• Web services are modular web applications that
  provide data and services to other applications
  over the web
• Web services apply web technologies such as HTTP
  and XML to the concepts of distributed computing
  technologies such as CORBA and DCOM

5
Present Web

• Common mans comment It is awesome.
• information sharing
• B2C, B2B
• search, mail, chat, RPC and what not?
• What is missing?
• automated interactions
• commonness between different distributed
  application technologies

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Evolution

Application
Application
Applications were stand-alone
User Interaction
API
Application
APIs used for interacting with applications
Application
User Interaction
SOAP LAYER
All interactions use SOAP unaware of API
involved
API
Application
Application
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Evolution (contd)

• Need for betterment
• Tomorrows Web
• automated interactions
• application level interactions
• distributed computing platform
• Answer web services
• Goals
• enable internet scale dynamic binding
• efficiently support both open web and more
  constrained environments
• universal availability and interoperability

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Vision

• Unified view of applications in heterogeneous
  systems on web
• Seamlessly integrate with existing platforms and
  programming models
• Distributed computing platform for the web
• Interface to access functionalities offered by
  information systems, application programs and
  business processes

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Web Service Definition

• A Web service is a software application
  identified by a URI, whose interfaces and
  binding are capable of being defined, described
  and discovered by XML artifacts and supports
  direct interactions with other software
  applications using XML based messages via
  Internet-based protocols. (W3C definition)
• - An association between an Interface, a
  concrete protocol and a data format

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Web Service Definition (contd)

• Web services are self contained, self-describing,
  modular applications that can be published,
  located, and invoked across the Web. (Tidwell,
  IBM, 2001)
• Web service applications are encapsulated,
  loosely coupled Web components that can bind
  dynamically to each other. (Curbera, IBM, 2001)

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Web Services Features

• Service Oriented Architecture (SOA) as opposed to
  application based (client-server, monolithic)
  architectures
• Web is a collection of services

Service Registry
Publish
Find
Service Provider
Service Requestor
Bind
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Features(contd)

• Create loosely coupled applications
• changing implementation of a function does not
  require change in invoking function
• Create encapsulated applications
• implementation is hidden from outside
• Allows integration of applications with deep
  interaction
• applications are unaware of APIs

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Features(contd)

• Allow reuse of Software Components
• reusable code that need not be written saving
  time, money and reducing risk
• Address Middleware issues over web
• without much complexity
• FYI Middleware is a high level software layer
  that provides a standardized interface to
  collection of distributed objects
• FYI Whats wrong with CORBA/RMI/COM ?
• dont talk to each other (some implementations
  do)
• tightly coupled with application
• different data representation, vendors and
  dialects
• RMI Java-to-Java only technology
• CORBA uses proprietary IIOP (typically blocked
  by Firewall) and interoperability of ORB
  implementations is not guaranteed
• COM/DCOM Microsoft only solution

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Features(contd)

• Based on messages, documents and not APIs
• shift in focus from how to invocate to what to
  invocate
• Can be complementary to CORBA, RMI, COM
• components are treated as services
• using WSDL1 as extended IDL2
• Common registry
• cross vendor, platform, industry
• widely accepted
• 1 Web Services Description Language
  2 Interface Description Language

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Features(contd)

• Operating system agnostic
• because it is XML (simple structured text) based
  technology
• Consistent architecture
• both inside and outside an enterprise
• application producer/consumer in different
  hardware
• regardless of development environment
• Allows composition
• combining and linking existing web services to
  create new web processes to perform a complex
  task

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How Web Services work?

• Web services are standards-based software
  components that can be accessed over the
  Internet.
• Step 1 Service providers (producer)
  maintain/publish information about their services
  in a registry
• Step 2 Service requesters (consumer) search
  registries for services
• Step 3 Once found, a service can be invoked
  based on open Internet standards irrespective of
  differences in platforms, programming model,
  programming languages between consumer and
  producer

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Web Services Standards

• With the following technologies, it is
  possible to build standards-based systems that
  are truly interoperable.
• UDDI Universal Description, Discovery and
  Integration.
• UDDI registry stores descriptions about companies
  and the services they offer in a common XML
  format. (for web services publishing and
  discovery)
• WSDL Web Services Description Language (new
  DAML-S)
• WSDL is an XML-based format for specifying the
  interface to a web service. (for web services
  description)
• SOAP Simple Object Access Protocol
• SOAP is the XML-based protocol for sending
  requests and responses to and from web services.
  (for web services invocation)
• WSFL Web Services Flow Language (new BPEL4WS)
• for web services composition

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Simple Web Service Invocation

• courtesyhttp//www.cs.uga.edu/sent/thesis/Final.
  ppt

Service Requestor
Remote Web Service Repository (Web Sites)
2
Manual Web Service Lookup
HTTP GET
3
WSDL File
Write Client Code
1
Remote Web service
4
SOAP Request
Invoke Web Service
Publish Web Service
5
SOAP Response
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Behind the scene

• Components required
• software which needs to be exposed as a web
  service
• SOAP Server (Apache Axis, SOAPLite, etc.)

SOAP Messages
Requestor
(http transport)
SOAP Client
Endpoint
Web Service Provider
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WSDL Structure
Service

• Service
• collection of endpoints
• endpoints port binding
• Port type
• set of operations supported by endpoints
• Operations
• abstract description of action supported by
  service
• Binding
• maps abstract specification to specific protocol
• Ports
• network address/URI that implements service
• Message
• typed definition of data communicated
• Used in conjunction with UDDI registry and can
  be compared with IDL
• courtesy http//www.llnl.gov/CASC/workshops/compo
  nents_2001/viewgraphs/FranciscoCurbera.ppt

Port (e.g. http//host/svc)
Port
Binding (e.g. SOAP)
Binding
Abstract interface
portType
operation(s)
inMesage
outMessage
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WSDL File

• Provides explicit representation of
  available protocols while in OMG model, protocol
  is fixed at the time ORB infrastructure is
  deployed. Protocol specification is not visible
  to application or developer

Abstract Description
Concrete Description
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SOAP Simple Object Access Protocol

• XML based lightweight protocol for the exchange
  of information in a decentralized, distributed
  environment
• What's so special about SOAP ?
• platform independent
• gets over firewall issues
• Why do we need it ?
• today's applications communicate using RPC using
  HTTP. But HTTP is not designed for this.
• ? introduces security and compatibility issues
• ? firewalls typically block
• How ?
• XML based messages (simple text and nothing else)

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SOAP

• SOAP defines a framework for message structure
  and a message-processing model
• Does not define application semantics
• Enables trans-operating system RPCs
• Used over HTTP, SMTP, FTP, MQSeries, Jabber, JMS
  etc
• lt?xml version"1.0" encoding"UTF-8" ?gt
• ltenvEnvelope xmlnsenv"http//www.w3.org/2001/09
  /soap-envelope"gt
• ltenvHeadergt
• ltnalertcontrol xmlnsn"http//example.org/aler
  tcontrol"gt
• ltnprioritygt1lt/nprioritygt
• ltnexpiresgt2001-06-22T140000-0500lt/nexpiresgt
• lt/nalertcontrolgt
• lt/envHeadergt
• ltenvBodygt
• ltmalert xmlnsm"http//example.org/alert"gt
• ltmmsggtPick up Mary at school at 2pmlt/mmsggt
• lt/malertgt
• lt/envBodygt
• lt/envEnvelopegt

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UDDI

• A shared public registry implementation based on
  a set of public specifications
• Specification for registry also defines a
  SOAP-based web service for locating
  WSDL-formatted protocol descriptions of web
  services
• Two types of information are registered within
  UDDI. The first is the set of abstract service
  protocols, called tModels (technical models),
  which are used to describe the behavior of a web
  service. The second type of information in UDDI
  is the service implementation, currently referred
  to as a businessEntity. These entries refer to
  multiple tModels and provide descriptions about
  their behavior and specifications.

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Web Services Composition

• Task of combining and linking existing web
  services to create new web processes.
• WHY ? (e.g.. Conference booking scenario)
• Adds value to the collection of services, by
  orchestrating them according to the requirement
  of the problem
• Types of Composition
• Static Composition - services to be composed are
  decided at design time
• Dynamic Composition - services to be composed are
  decided at run-time
• WSFL, XLANG, BPEL4WS, DAML-S are some of the XML
  languages that have been proposed for specifying
  a web service composition

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Challenges and my ongoing work in Web Services

• Semantics based discovery of web services
• WSDL, UDDI do not support description and
  publishing services based on capabilities
• present discovery is based on key word search
  (e.g.. Ticket Service). Not efficient.
• solution Ontology based description and
  discovery of web services
• achieves semantic mark up to web services and
  provides semantic interoperability
• Dynamic composition
• QoS, service agreements, security
• Harmonizing transactional behavior, reliably
  executing and monitoring messages

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Summary

• Web Services
• framework is being defined, standardized
• standards are still in flux
• received wide acceptance in industry as an
  e-business (r)evolution
• provides increased flexibility in software
  deployment
• offers a cost effective way to maintain and
  integrate legacy IT systems at a lower cost than
  typical enterprise application integration
  efforts
• could be next-generation EDI
• could be used as middleware for internet level
  applications

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Wrap up

• Hopefully you understood in this session
• 1. what a web service is
• 2. advantages of using it
• 3. value addition by composition
• 4. what has been done so far in web services?
• 5. what can be done in future w.r.t. WS?

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Questions

• and hopefully answers
• mailtokaart_at_cs.uga.edu
• http//www.arches.uga.edu/kaarthik

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For more information

• http//www.uddi.org
• http//www.w3.org/2002/ws/
• http//java.sun.com/webservices/docs/1.0/tutorial/
  
• http//www.alphaworks.ibm.com/webservices
• http//edocs.bea.com/wls/docs70/webserv/index.html
  
• http//xml.apache.org/
• http//www.xml.com/pub/a/2001/04/04/webservices/
• http//www-3.ibm.com/software/solutions/webservice
  s/
• http//www.w3c.org/TR/wsdl
• http//www.w3c.org/TR/soap
• http//chief.cs.uga.edu/jam/webwork/geneflow/pape
  rs/wspapers.html