Introduction to Web Services

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Introduction to Web Services

• Vladimir Tosic
• NSERC Post-Doctoral Fellow
• Department of Computer Science
• University of Western Ontario, London, Canada
• http//elab.njit.edu/vladimir

2
How Do Web Services Relate to Your Course?

• Relatively novel XML-based distributed/network
  computing paradigm
• Supported by all major computing companies
  (Microsoft, IBM, Sun, Oracle, HP, )
• Evolution of older distributed computing
  technologies (e.g., RPC, CORBA)
• Many technical similarities
• The main difference is in business issues

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Lecture Outline

1. What are Web Services?
2. Web Service technologies
3. Examples
4. Web Service tools
5. Web Service resources
6. Discussion
7. Conclusions

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What are Web Services? - Outline

• Service-based software systems
• The Publish-Find-Bind interaction model
• Definition of a Web service
• Some goals of the work on Web services
• Web services vs. distributed objects
• Who is working in this area?

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Service-Based Software Systems

• Software is a service business model
• Software is not a product any more, but a service
  available over the network
• Application Service Providers (ASPs)
• Service-Oriented Architecture (SOA)
• Applications decomposed into distributed services
• On-line access to libraries of composable
  components
• CORBA, Jini, Component Service Providers (CSPs)

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The Publish-Find-Bind Interaction Model
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W3C Definition of a Web Service

• A software application that
• has a unique Uniform Resource Identifier (URI),
• can be defined, described, and discovered using
  XML (Extensible Markup Language),
• supports exchange of XML messages via
  Internet-based protocols.

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Microsoft .NETDefinition of a Web Service

• A black-box programmable application logic that
  can be reused without worrying about how the
  service is implemented
• Defined strictly in terms of the messages the Web
  Service accepts and generates
• Simply and easily composed over the network,
  across domain boundaries
• Accessible using standard and ubiquitous Internet
  protocols and data formats (XML)

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Some Goals of the Work on Web Services

• Faster development and deployment of IT
  (Information Technology) systems
• Dynamic and ad hoc A2A (Application-to-Application
  ) and B2B (Business-to-Business) integration
• Interoperability across programming languages and
  operation platforms
• Leveraging and compatibility with existing
  Internet/Web infrastructure

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Web Services (WS) vs. Distributed Objects (DO)

• (WS) Ad hoc temporary vs.
• (DO) planned stable integration
• (WS) loose vs. (DO) tight coupling
• (WS) Synchronous or asynchronous vs.
• (DO) only synchronous communication
• (WS) RPC or document-based vs.
• (DO) only RPC interactions
• (WS) B2B or intra-enterprise vs.
• (DO) only intra-enterprise integration

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Who Is Working in This Area?

• All major computing companies
• Microsoft .NET, IBM Dynamic e-business, Sun ONE
  (Open Net Environment), Oracle, HP,
• Several industrial standardization bodies
• W3C (World Wide Web Consortium)
• OASIS (Organization for the Advancement of
  Structured Information Standards)
• WS-I (Web Services - Interoperability)

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Overview of Technologies

1. What are Web Services?
2. Web Service technologies
3. Details and examples
4. Web Service tools
5. Web Service resources
6. Discussion
7. Conclusions

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Basic Technologies

• XML (Extensible Markup Language) - For data
  representations
• SOAP a.k.a. Simple Object Access Protocol, XML
  Protocol - An XML packaging protocol, defines
  message formats and encoding rules
• WSDL (Web Services Description Language) - An XML
  service description language

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Some Popular Technologies

• UDDI (Universal Description, Discovery, and
  Integration) - For discovering service providers
  if you do not know their URLs
• BPEL4WS (Business Process Execution Language for
  Web Services) - For describing Web Service
  compositions (orchestrations)

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And Many Other Technologies

• WSLA (Web Service Level Agreements) - A way to to
  specify quality of service (QoS) guarantees and
  service level agreements
• Many WS-??? and WS?L technologies

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And Now Something Concrete

1. What are Web Services?
2. Web Service technologies
3. Details and examples
4. Web Service tools
5. Web Service resources
6. Discussion
7. Conclusions

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Details and Examples - Outline

• A brief summary of XML
• Features of the SOAP packaging protocol
• Structure of a SOAP message
• XML elements of WSDL documents
• Structure of a WSDL document
• Examples

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A Brief Summary of XML

• A textual, platform-independent format for
  structured data representation
• Looks like HTML (HyperText Markup Language), but
  you can define your own tags
• Markup contains information about data
• Elements and attributes
• Structure defined using XML Schema
• Parsers check well-formedness and validity

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The SOAP Packaging Protocol

• Defines the structure of XML messages and XML
  encoding rules for various data types
• Supports both RPC-style and document-style
  interactions
• XML encoding rules used only for RPC-style
• Can be used with various transport protocols
• Most often used with HTTP (HyperText Transport
  Protocol)

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Structure of a SOAP Message
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Elements of WSDL Documents (1/3)

• Used for XML description of Web Services
• Can be used with various XML packaging and
  transport protocols
• The main XML elements in WSDL 1.1 documents
• (new WSDL 2.0 not yet widely used)
• definitions - defines namespaces and contains
  other WSDL elements
• types - defines data types used

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Structure of a WSDL Document

• descriptions
• types
• message
• part
• port type
• operation
• binding
• service
• port

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Elements of WSDL Documents (2/3)

• message - defines name and parameters of one
  message (a portion of an operation)
• part - defines name and data type of a message
  parameter
• port type - contains one or more operations (
  interface)
• operation - groups input, output, and/or fault
  messages

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Types of Operations in WSDL 1.1

1. One-way (input only)
2. Request-response (input, output, and optional
   fault message)
3. Solicit-response (output, input, and optional
   fault message)
4. Notification (output only)

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Elements of WSDL Documents (3/3)

• binding - defines the message packaging protocol
  and transport protocol used for a port type
• service - groups related ports and defines the
  name of the Web Service
• port ( endpoint) - associates a binding with a
  network address
• Other WSDL elements (e.g., description)

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Examples - Simple Stock Web Services

• SOAP www.w3schools.com/soap/soap_example.asp
• WSDL www.brics.dk/amoeller/WWW/webservices/wsdle
  xample.html
• UDDI www.brics.dk/amoeller/WWW/webservices/uddie
  xamples.html

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Tools Make Life Easier

1. What are Web Services?
2. Web Service technologies
3. Details and examples
4. Web Service tools
5. Web Service resources
6. Discussion
7. Conclusions

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Some Popular Web Service Tools

• XML and WSDL writing tools
• Altova XMLSpy,
• SOAP engines
• facilitate development of SOAP applications
• process SOAP messages
• have tools for WSDL lt-gt Java generation
• UDDI registries and tools
• IBM public UDDI registry and IBM UDDI4J,

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Some Popular SOAP Engines

• Apache Axis
• IBM WSTK (Web Services Toolkit)
• IBM WebSphere
• BEA WebLogic
• Systinet WASP
• The Mind Electric GLUE

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A Typical Provider Web Service
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A Typical SOAP Engine
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To Probe Further

1. What are Web Services?
2. Web Service technologies
3. Details and examples
4. Web Service tools
5. Web Service resources
6. Discussion
7. Conclusions

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Web Service Resources

• Books (by OReilly, SAMS, )
• Magazines (e.g., Web Services Journal)
• Conference proceedings (ICWS, SCC, )
• On-line communities and portals
• Company Web Sites
• Web sites of university research groups
• gt http//elab.njit.edu/vladimir/
  WSwebliography.html

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What are the Issues?

1. What are Web Services?
2. Web Service technologies
3. Details and examples
4. Web Service tools
5. Web Service resources
6. Discussion
7. Conclusions

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Discussion Points - Outline

• Some potential advantages of Web Services
• Some potential disadvantages
• Your thoughts and questions
• Summary of my research

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Some Potential Advantages

• Flexibility
• Wide industry support
• Bottom-up approach to standards
• Low entry barrier
• Accommodating legacy systems
• Leveraging widely used technologies (Internet,
  HTTP, XML)
• Basis for the Semantic Web, Grid computing

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Some Potential Disadvantages

• A lot of hype and marketing
• Not exactly software revolution, Reinventing
  the wheel
• Overall infrastructure complexity hidden
• Actual degree of loose coupling
• Performance
• Many puzzle pieces are still in progress

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Your Thoughts and Questions

• What do you think?
• What do you want me to clarify or explain in more
  detail?

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Summary of My Research

• Management of Web Services
• New stream mobile/embedded environments
• Web Service Offerings Language (WSOL)
• Specification of management information (service
  offerings classes of service, constraints,
  prices/ penalties, management statements, )
• Web Service Offerings Infrastructure (WSOI)
• Monitoring enforcement of WSOL descriptions
• Dynamic manipulation of service offerings

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Things to Remember!

1. What are Web Services?
2. Web Service technologies
3. Details and examples
4. Web Service tools
5. Web Service resources
6. Discussion
7. Conclusions

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Conclusions

• Web Services have URIs and use XML for
  description, discovery, and data transfer
• The main technologies are XML, SOAP, WSDL
• There are many other technologies
• Key technical concepts are not revolutionary
• There are very powerful political games around
  Web Services
• Many open research issues

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Thank You!

• Vladimir Tosic
• NSERC Post-Doctoral Fellow
• Department of Computer Science
• University of Western Ontario, London, Canada
• http//elab.njit.edu/vladimir