Biyernes, Agosto 29, 2014

Web Services

Web Services
A Web service is a method of communication between two electronic devices over a network. It is a software function provided at a network address over the web with the servicealways on as in the concept of utility computing. The W3C defines a Web service generally as:
a software system designed to support interoperable machine-to-machine interaction over a network.[1]
[a web service] has an interface described in a machine-processable format (specifically WSDL). Other systems interact with the Web service in a manner prescribed by its description using SOAP (Simple Object Access Protocol) messages, typically conveyed using HTTP with an XML serialization in conjunction with other Web-related standards.[1]
Most web services do not adopt this complex architecture.[citation needed] This article describes it in more detail.
The W3C also states:
We can identify two major classes of Web services:
  • REST-compliant Web services, in which the primary purpose of the service is to manipulate XML representations of Web resources using a uniform set ofstateless operations; and
  • Arbitrary Web services, in which the service may expose an arbitrary set of operations.[2]
Automated tools can aid in the creation of a web service. For services using WSDL, it is possible to either automatically generate WSDL for existing classes (a bottom-up model) or to generate a class skeleton given existing WSDL (a top-down model).
  • A developer using a bottom-up model writes implementing classes first (in some programming language), and then uses a WSDL generating tool to expose methods from these classes as a web service. This is simpler to develop but may be harder to maintain if the original classes are subject to frequent change.[4]
  • A developer using a top-down model writes the WSDL document first and then uses a code generating tool to produce the class skeleton, to be completed as necessary. This model is generally considered more difficult but can produce cleaner designs and is generally more resistant to change. As long as the message formats between sender and receiver do not change, changes in the sender and receiver themselves do not affect the web service. The technique is also referred to ascontract first since the WSDL (or contract between sender and receiver) is the starting point.[5]

Web services that use markup languages[edit]

There are a number of web services that use markup languages:

Criticisms[edit]

Critics of non-RESTful web services often complain that they are too complex[6] and based upon large software vendors or integrators, rather than typical open sourceimplementations.
There are also concerns about performance due to web services' use of XML as a message format and SOAP/HTTP in enveloping and transporting.[7]

Regression Testing of Web service[edit]

Functional and non-functional web service testing is done with the help of WSDL parsing and regression testing is performed by identifying the changes made thereafter. Web service regression testing needs can be categorized in three different ways, namely, changes in WSDL, changes in code, and selective re-testing of web service operations. To capture the above, three intermediate forms of WSDL, namely, Difference WSDL (DWSDL), Unit WSDL (UWSDL), and Reduced WSDL (RWSDL), respectively can be used. These intermediate forms are then combined to form Combined WSDL (CWSDL) which is further used for regression testing of the web service. This will help in Automatic Web Service Change Management (AWSCM), by performing the selection of the relevant test cases to construct a reduced test suite from the old test suite. [8] Source: wikipedia
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