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Web Service

Web Service. Ahmed Gamal Ahmed Nile University Bioinformatics Group. Agenda. Web Service Over View SOAP WSDL UDDI. Web Service Over View. What are Web services?

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Web Service

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  1. Web Service Ahmed Gamal Ahmed Nile University Bioinformatics Group

  2. Agenda • Web Service Over View • SOAP • WSDL • UDDI

  3. 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.

  4. 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.

  5. 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

  6. 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.

  7. Web Service Over View

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Web Service Over View

  17. XML—The Backbone of Web Services

  18. XML—The Backbone of Web Services

  19. XML—The Backbone of Web Services • The XML markup, in much the same way as HTML, is in the form of tags(e.g., <tag>, <name>, <price>, <wife>, and so forth).

  20. XML—The 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.

  21. XML—The Backbone of Web Services • This XML carries HTML table information: • This XML carries information about a table (a piece of furniture):

  22. XML—The Backbone of Web Services • Solving the Name Conflict Using a Prefix Name conflicts in XML can easily be avoided using a name prefix.

  23. XML—The 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. xmlns:prefix="URI".

  24. XML—The Backbone of Web Services The namespace URI is NOT used by the parser to look up information.

  25. Web Service Stack

  26. Basic Web Service Usage Scenario

  27. 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

  28. 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

  29. 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

  30. SOAP – Simple Object Access ProtocolExample: SOAP Message

  31. 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

  32. 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

  33. 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)

  34. WSDL – Web Service Description Language Example: Overall Document Structure

  35. WSDL – Web Service Description Language Example: Definition of Types

  36. WSDL – Web Service Description Language Example: Definition of Messages and PortType

  37. WSDL – Web Service Description Language Example: Definition of Binding and Service

  38. 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:

  39. 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

  40. 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

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