WebServices
key functional components:
Service Implementation:
Build from scratch, provide a wrapper, or create a new service interface for an existing Web Service.
Publication:
Author the WSDL document, publish the WSDL on a Web Server, and publish the existence of your WSDL in a Web Services registry using a standard specification (UDDI).
Discovery:
Search the registry, get the URL, and download the WSDL file. –Invocation: •Author a client (SOAP) using the WSDL and make the request (SOAP message) and get the response (SOAP message).
Service Implementation:
Build from scratch, provide a wrapper, or create a new service interface for an existing Web Service.
Publication:
Author the WSDL document, publish the WSDL on a Web Server, and publish the existence of your WSDL in a Web Services registry using a standard specification (UDDI).
Discovery:
Search the registry, get the URL, and download the WSDL file. –Invocation: •Author a client (SOAP) using the WSDL and make the request (SOAP message) and get the response (SOAP message).
Overview
1. Client queries registry to locate service.
2. Registry refers client to WSDL document.
3. Client accesses WSDL document.
4. WSDL provides data to interact with Web service.
5. Client sends SOAP-message request.
6. Web service returns SOAP-message response.
Stages of Web services Development and Deployment:
Creation – Design, development, documentation, testing, and distribution.
Publication – Web service hosting and maintenance.
Promotion – Directory services, value-added services and accreditation.
2. Registry refers client to WSDL document.
3. Client accesses WSDL document.
4. WSDL provides data to interact with Web service.
5. Client sends SOAP-message request.
6. Web service returns SOAP-message response.
Stages of Web services Development and Deployment:
Creation – Design, development, documentation, testing, and distribution.
Publication – Web service hosting and maintenance.
Promotion – Directory services, value-added services and accreditation.
Structure:
A program sends a request to a remote Web service containing an XML message and (optionally) receives a response.
A minimal web service has three components:
The Service: a software component which is capable of processing an XML document. –Transport, programming language etc is not important
The Document: the XML document that –contains all of the application-specific information.
The Address: describes the protocol binding (e.g. TCP or HTTP) & network address that can be used to access the service. –also called a port-reference.
Features:
Support Document Exchange:
XML containing document-oriented or procedural-oriented information.
Standardization:
Based on standardized XML and supported globally by most major technology firms.
Interoperability:
XML is at the data transport level.
Loosely Coupled:
The abstraction web server interface (WSDL) from its implementation decouples the logic of the client and the server.
–makes it much easier to change back-end implementation without the client needing to update their code.
Course-grained:
Course-grained model e.g. fine grained = Java method but Web Service typically combine several fine-grained operation to expose collective.
Supports RPC:
Support remote procedure calls (built into SOAP) via and XML-based protocol.
Web Service Development:
Green field:
Developer starts from scratch, creating not only the Web service but also the application functionality being exposed as a Web service.
Bottom up:
Functionality being exposed as a Web service (i.e. the back-end application) already exists.
Top down:
Start with an existing Web service interface and then create the application functionality capable of implementing that interface.
Meet in the middle:
Combination – the Web services interface (abstract WSDL) and existing application code exists already –need to integrate them by creating a bridge.
