Post on 02-Apr-2015
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.
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.
Basic ArchitectureThe basic architecture includes Web services
technologies capable of:Exchanging messagesDescribing Web servicesPublishing and discovering Web service
descriptions
Web Service Over View
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.
Web Service Over View
Web Service Over View
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.
Web Service Over View
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.
Web Service Over View
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.
Web Service Over View
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.
Web Service Over View
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.
Web Service Over View
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.
Web Service Over View
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.
Web Service Over View
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.
Web Service Over View
Web Service Over View
XML—The Backbone of Web Services
XML—The Backbone of Web Services
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—The Backbone of Web Services
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.
XML—The Backbone of Web Services
This XML carries HTML table information:
This XML carries information about a table (a piece of furniture):
XML—The Backbone of Web Services
Solving the Name Conflict Using a PrefixName conflicts in XML can easily be avoided using a name prefix.
XML—The Backbone of Web Services
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".
XML—The Backbone of Web Services
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