Web Service

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Web Service

• Ahmed Gamal Ahmed
• Nile University
• Bioinformatics Group

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Agenda

• Web Service Over View
• SOAP
• WSDL
• UDDI

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Web Service Over View

• What are Web services?
• a standardized way of integrating Web-based
  applications using the XML, SOAP, WSDL and UDDI
  open standards over an Internet protocol
  backbone.
• XML is used to tag the data
• SOAP is used to transfer the data
• WSDL is used for describing the services
  available
• UDDI is used for listing what services are
  available.

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Web Service Over View

• Why there is a need for Web services?
• Web services' distributed computing model allows
  application-to-application communication.
• Web services allow different applications from
  different sources to communicate with each other
  without time-consuming custom coding, and because
  all communication is in XML, Web services are not
  tied to any one operating system or programming
  language.
• Because of this level of application
  integration, Web services have grown in
  popularity and are beginning to improve business
  processes. In fact, some even call Web services
  the next evolution of the Web.

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Web Service Over View

• Basic Architecture
• The basic architecture includes Web services
  technologies capable of
• Exchanging messages
• Describing Web services
• Publishing and discovering Web service
  descriptions

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Web Service Over View

• Service-Oriented Architecture
• SOA is a specific architectural style that is
  concerned with loose coupling and dynamic binding
  between services. Some critically important
  factors at the heart of SOA are necessary to make
  it work effectively.

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Web Service Over View
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Web Service Over View

• Components
• The Service
• A service is a software module deployed on
  network accessible platforms provided by the
  service provider.
• It exists to be invoked by or to interact with a
  service requestor.
• It may also function as a requestor, using other
  web services in its implementation.

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Web Service Over View

• Components
• The Service Description
• The service description contains the details of
  the interface and implementation of the service.
• This includes its data types, operations, binding
  information, and network location.
• It could also include categorization and other
  meta data to facilitate discovery and utilization
  by requestors.
• The service description may be published to a
  requestor directly or to a discovery agency.

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Web Service Over View

• Roles
• Service Provider
• From a business perspective, this is the owner
  of the service.
• From an architectural perspective, this is the
  platform that hosts access to the service.
• It has also been referred to as a service
  execution environment or a service container.
• Its role in the client-server message exchange
  patterns is that of a server.

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Web Service Over View

• Roles
• Service Requestor
• From a business perspective, this is the business
  that requires certain function to be satisfied.
• From an architectural perspective, this is the
  application that is looking for and invoking or
  initiating an interaction with a service.
• The requestor role can be played by a browser
  driven by a person or a program without a user
  interface, e.g. another web service.
• Its role in the client-server message exchange
  patters is that of a client.

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Web Service Over View

• Roles
• Discovery Agency
• This is a searchable set of service descriptions
  where service providers publish their service
  descriptions.
• The service discovery agency can be centralized
  or distributed.
• A discovery agency can support both the pattern
  where it has descriptions sent to it and where
  the agency actively inspects public providers for
  descriptions.
• Service requestors may find services and obtain
  binding information (in the service descriptions)
  during development for static binding, or during
  execution for dynamic binding.

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Web Service Over View

• Operations
• Publish
• In order to be accessible, a service needs to
  publish its description such that the requestor
  can subsequently find it.
• Where it is published can vary depending upon the
  requirements of the application.

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Web Service Over View

• Operations
• Find
• The service requestor retrieves a service
  description directly or queries the registry for
  the type of service required .
• The find operation may be involved in two
  different lifecycle phases for the service
  requestor
• At design time in order to retrieve the service's
  interface description for program development
• At runtime in order to retrieve the service's
  binding and location description for invocation.

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Web Service Over View

• Operations
• Interact Eventually, a service needs to be
  invoked. In the interact operation the service
  requestor invokes or initiates an interaction
  with the service at runtime using the binding
  details in the service description to locate,
  contact, and invoke the service. Examples of the
  interaction include single message one way,
  broadcast from requester to many services, a
  multi message conversation, or a business
  process. Any of these types of interactions can
  be synchronous or asynchronous.

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Web Service Over View
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XMLThe Backbone of Web Services
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XMLThe Backbone of Web Services
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XMLThe Backbone of Web Services

• The XML markup, in much the same way as HTML, is
  in the form of tags(e.g., lttaggt, ltnamegt, ltpricegt,
  ltwifegt, and so forth).

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XMLThe Backbone of Web Services

• XML namespaces
• Name Conflicts
• In XML, element names are defined by the
  developer. This often results in a conflict when
  trying to mix XML documents from different XML
  applications.

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XMLThe Backbone of Web Services

• This XML carries HTML table information
• This XML carries information about a table (a
  piece of furniture)

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XMLThe Backbone of Web Services

• Solving the Name Conflict Using a Prefix
• Name conflicts in XML can easily be avoided
  using a name prefix.

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XMLThe Backbone of Web Services

• XML Namespaces - The xmlns Attribute
• When using prefixes in XML, a so-called namespace
  for the prefix must be defined.
• The namespace is defined by the xmlns attribute
  in the start tag of an element.
• The namespace declaration has the following
  syntax. xmlnsprefix"URI".

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XMLThe Backbone of Web Services

• The namespace URI is NOT used by the parser to
  look up information.

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Web Service Stack
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Basic Web Service Usage Scenario
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Web Services Implementation

• Application Server (web service-enabled)
• provides implementation of services and
  exposes it through WSDL/SOAP
• implementation in Java, as EJB, as .NET (C)
  etc.
• SOAP server
• implements the SOAP protocol
• HTTP server
• standard Web server
• SOAP client
• implements the SOAP protocol on the client site

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SOAP Simple Object Access Protocol

• SOAP consists of
• Envelope construct defines the overall
  structure of messages
• Encoding rules define the serialization of
  application data types
• SOAP RPC defines representation of remote
  procedure calls and responses
• Binding framework binding to protocols such
  as HTTP, SMTP
• Fault handling
• Soap supports advanced message processing
• forwarding intermediaries route messages
  based on the semantics of message
• active intermediaries do additional
  processing before forwarding messages, may modify
  message

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SOAP Simple Object Access ProtocolSOAP Messages

• SOAP messages consist of
• Envelope top element of XML message
  (required)
• Header general information on message such as
  security (optional)
• Body data exchanged (required)
• Header
• elements are application-specific
• may be processed and changed by
• intermediaries or recipient
• Body
• elements are application-specific
• processed by recipient only

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SOAP Simple Object Access ProtocolExample
SOAP Message
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SOAP Simple Object Access ProtocolProtocol
Binding

• Bindings to different protocols possible HTTP,
  SMTP
• Different HTTP bindings HTTP POST, HTTP GET
• standard HTPP POST for request-response

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WSDL Web Service Description Language

• Description of Web services in XML format
• abstract description of operations and their
  parameters (messages)
• binding to a concrete network protocol (e.g.
  SOAP)
• specification of endpoints for accessing the
  service
• Structure of a WSDL document

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WSDL Web Service Description Language
Overview of Defining WSDL Services

• Define in XML Schema the message types used when
  invoking the service MT1, MT2 etc.
• Define (named) messages by using these types,
  e.g.
• message m1 has type MT1
• message m2 has type MT2 etc.
• Define Services that consist of one or more
  operations each operation is implemented by the
  exchange of messages
• service S offers operation O1 for executing O1
  first send a request message m1, then a response
  message m2 is returned
• Define a Binding B to a specific protocol, e.g.
  SOAP
• service S is implemented in SOAP the SOAP
  messages are constructed from the abstract
  messages m1 and m2 by, e.g. inlining the message
  as body of SOAP messages
• Service S is provided with binding B at the
  following URI's (called ports)

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WSDL Web Service Description Language
Example Overall Document Structure

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WSDL Web Service Description Language
Example Definition of Types

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WSDL Web Service Description Language
Example Definition of Messages and PortType

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WSDL Web Service Description Language
Example Definition of Binding and Service

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WSDL Web Service Description LanguagePortTypes

• WSDL supports 4 message patterns that an endpoint
  (service provider!) can support for an operation
• one-way message is sent to service provider
  without expecting response
• request-response request is sent to service
  provider expecting response
• solicit-response provider sends a message and
  expects response
• notification message is sent by service provider
• Message patterns are distinguished by the use of
  input/output elements
• one way
• request/response

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UDDI Universal Description Discovery and
Integration

• Universal Description and Discovery and
  Integration
• UDDI consists of
• A specification for how to build a registry of
  business, services and how to connect to them
• A standards committee that is working on revising
  and improving the specification
• Agreement to operate solutions that conform to
  the specification

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UDDI Universal Description Discovery and
Integration

• UDDI Business Registry consist of
• White pages general information regarding
  business
• Yellow pages arranged by geography or industry
  code
• Green pages list protocols supported by each
  business
• Information stored in XML format