ahmed gamal ahmed nile university bioinformatics group

Ahmed Gamal AhmedNile University

Bioinformatics Group

AgendaWeb Service Over ViewSOAPWSDLUDDI

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 dataSOAP is used to transfer the data WSDL is used for describing the services

availableUDDI is used for listing what services are

available.


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.

Basic ArchitectureThe basic architecture includes Web services

technologies capable of:Exchanging messagesDescribing Web servicesPublishing and discovering Web service

descriptions


Service-Oriented ArchitectureSOA 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.


Components1.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.


Components2.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.


Roles1.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.


Roles2.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.


Roles2.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.


Operations1.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.


Operations2.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:

i. At design time in order to retrieve the service's interface description for program development

ii.At runtime in order to retrieve the service's binding and location description for invocation.


OperationsInteract: 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.


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).


XML namespacesName ConflictsIn XML, element names are defined by the

developer. This often results in a conflict when trying to mix XML documents from different XML applications.


This XML carries HTML table information:

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


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


XML Namespaces - The xmlns AttributeWhen 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".


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

Web Service Stack

Basic Web Service Usage Scenario

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

Web Services Implementation

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

SOAP – Simple Object Access Protocol

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 recipientBody– elements are application-specific– processed by recipient only

SOAP – Simple Object Access ProtocolSOAP Messages

SOAP – Simple Object Access ProtocolExample: SOAP Message

Bindings to different protocols possible: HTTP, SMTP

Different HTTP bindings: HTTP POST, HTTP GET

– standard HTPP POST for request-response

SOAP – Simple Object Access ProtocolProtocol Binding

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

WSDL – Web Service Description Language

1. Define in XML Schema the message types used when invoking the service: MT1, MT2 etc.

2. Define (named) messages by using these types, e.g. message m1 has type MT1 message m2 has type MT2 etc.

3. 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

4. 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

5. Service S is provided with binding B at the following URI's (called ports)

WSDL – Web Service Description Language Overview of Defining WSDL Services

WSDL – Web Service Description Language Example: Overall Document Structure

WSDL – Web Service Description Language Example: Definition of Types

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

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

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:

WSDL – Web Service Description LanguagePortTypes

Universal Description and Discovery and Integration

UDDI consists ofA specification for how to build a registry of

business, services and how to connect to themA standards committee that is working on

revising and improving the specificationAgreement to operate solutions that conform to

the specification

UDDI – Universal Description Discovery and Integration

UDDI Business Registry consist ofWhite pages – general information regarding

businessYellow pages – arranged by geography or

industry codeGreen pages – list protocols supported by each

businessInformation stored in XML format

UDDI – Universal Description Discovery and Integration

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