ⓘ Web service



A Uniform Resource Locator, colloquially termed a web address, is a reference to a web resource that specifies its location on a computer network and a mechanism for retrieving it. A URL is a specific type of Uniform Resource Identifier, although many people use the two terms interchangeably. URLs occur most commonly to reference web pages, but are also used for file transfer, email, database access, and many other applications. Most web browsers display the URL of a web page above the page in an address bar. A typical URL could have the form, which indicates a protocol http, a hostname ww ...


Knowledge market

A knowledge market is a mechanism for distributing knowledge resources. There are two views on knowledge and how knowledge markets can function. One view uses a legal construct of intellectual property to make knowledge a typical scarce resource, so the traditional commodity market mechanism can be applied directly to distribute it. An alternative model is based on treating knowledge as a public good and hence encouraging free sharing of knowledge. This is often referred to as attention economy. Currently there is no consensus among researchers on relative merits of these two approaches.


Hypertext Transfer Protocol

The Hypertext Transfer Protocol is an application protocol for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web, where hypertext documents include hyperlinks to other resources that the user can easily access, for example by a mouse click or by tapping the screen in a web browser. Development of HTTP was initiated by Tim Berners-Lee at CERN in 1989. Development of early HTTP Requests for Comments RFCs was a coordinated effort by the Internet Engineering Task Force IETF and the World Wide Web Consortium W3C, with ...

Web service

ⓘ Web service

The term Web service is either:

  • a server running on a computer device, listening for requests at a particular port over a network, serving web documents, and creating web applications services, which serve in solving specific domain problems over the Web
  • a service offered by an electronic device to another electronic device, communicating with each other via the World Wide Web, or

In a Web service a Web technology such as HTTP - originally designed for human-to-machine communication - is used for transferring machine-readable file formats such as XML and JSON.

In practice, a Web service commonly provides an object-oriented Web-based interface to a database server, utilized for example by another Web server, or by a mobile app, that provides a user interface to the end-user. Many organizations that provide data in formatted HTML pages will also provide that data on their server as XML or JSON, often through a Web service to allow syndication, for example, Wikipedias Export. Another application offered to the end-user may be a mashup, where a Web server consumes several Web services at different machines and compiles the content into one user interface.


1.1. Web services generic Asynchronous JavaScript And XML

Asynchronous JavaScript And XML AJAX is a dominant technology for Web services. Developing from the combination of HTTP servers, JavaScript clients and Plain Old XML as distinct from SOAP and W3C Web Services, now it is frequently used with JSON as well as, or instead of, XML.


1.2. Web services generic REST

Representational State Transfer REST is an architecture for well-behaved Web services that can function at Internet scale.

In a 2004 document, the W3C sets following REST as a key distinguishing feature of Web services:

We can identify two major classes of Web services:

  • arbitrary Web services, in which the service may expose an arbitrary set of operations.
  • REST-compliant Web services, in which the primary purpose of the service is to manipulate XML representations of Web resources using a uniform set of stateless operations; and

1.3. Web services generic Web services that use markup languages

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

  • WS-MetadataExchange
  • Web Services Flow Language WSFL, superseded by BPEL
  • Web template
  • Representational state transfer REST versus remote procedure call RPC
  • XML Interface for Network Services XINS, provides a POX-style web service specification format
  • Web Services Conversation Language WSCL
  • Web Services Description Language WSDL, developed by the W3C

1.4. Web services generic Web API

A Web API is a development in Web services where emphasis has been moving to simpler representational state transfer REST based communications. Restful APIs do not require XML-based Web service protocols SOAP and WSDL to support their interfaces.


2. W3C Web services

In relation to W3C Web services, the W3C defined a Web service as:

A web service is a software system designed to support interoperable machine-to-machine interaction over a network. It 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-messages, typically conveyed using HTTP with an XML serialization in conjunction with other web-related standards.

W3C Web Services may use SOAP over HTTP protocol, allowing less costly more efficient interactions over the Internet than via proprietary solutions like EDI/B2B. Besides SOAP over HTTP, Web services can also be implemented on other reliable transport mechanisms like FTP. In a 2002 document, the Web Services Architecture Working Group defined a Web services architecture, requiring a standardized implementation of a "Web service."


2.1. W3C Web services Explanation

The term "Web service" describes a standardized way of integrating Web-based applications using the XML, SOAP, WSDL and UDDI open standards over an Internet Protocol backbone. XML is the data format used to contain the data and provide metadata around it, SOAP is used to transfer the data, WSDL is used for describing the services available and UDDI lists what services are available.

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 service always-on as in the concept of utility computing.

Many organizations use multiple software systems for management. Different software systems often need to exchange data with each other, and a Web service is a method of communication that allows two software systems to exchange this data over the Internet. The software system that requests data is called a service requester, whereas the software system that would process the request and provide the data is called a service provider.

Different software may use different programming languages, and hence there is a need for a method of data exchange that doesnt depend upon a particular programming language. Most types of software can, however, interpret XML tags. Thus, Web services can use XML files for data exchange.

Rules for communication between different systems need to be defined, such as:

  • How one system can request data from another system.
  • What error messages to display when a certain rule for communication is not observed, to make troubleshooting easier.
  • What would be the structure of the data produced.
  • Which specific parameters are needed in the data request.

All of these rules for communication are defined in a file called WSDL Web Services Description Language, which has a.wsdl extension. Proposals for Autonomous Web Services AWS seek to develop more flexible Web services that do not rely on strict rules)

A directory called UDDI defines which software system should be contacted for which type of data. So when one software system needs one particular report/data, it would go to the UDDI and find out which other systems it can contact for receiving that data. Once the software system finds out which other systems it should contact, it would then contact that system using a special protocol called SOAP Simple Object Access Protocol. The service provider system would first validate the data request by referring to the WSDL file, and then process the request and send the data under the SOAP protocol.


2.2. W3C Web services Automated design methods

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 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 the 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 as contract first since the WSDL or contract between sender and receiver is the starting point.
  • 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.
  • A developer using a Subset SWSDL i.e. a WSDL with the subset operation in the original WSDL can perform Web service testing and top-down development.


2.3. W3C Web services Criticism

Critics of non-RESTful Web services often complain that they are too complex and based upon large software vendors or integrators, rather than typical open source implementations.

There are also concerns about performance due to Web services use of XML as a message format and SOAP/HTTP in enveloping and transporting.


2.4. W3C Web services Regression testing of Web services

Functional and non-functional testing of Web services is done with the help of WSDL parsing. Regression testing is performed by identifying the changes made to upgrade software. Web service regression testing needs can be categorized in three different ways, namely, changes in WSDL, changes in the code, and selective re-testing of operations. We can capture the above three needs in three intermediate forms of Subset WSDL, namely, Difference WSDL DWSDL, Unit WSDL UWSDL, and Reduced WSDL RWSDL, respectively. These three Subset WSDLs are then combined to form Combined CWSDL that is further used for regression testing of the Web service. This will help in Automated 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.

Web services testing can also be automated using several test automation tools like SOAP UI, Oracle Application Testing Suite OATS, Unified Functional Testing, Selenium, etc.


2.5. W3C Web services Web service change management

Work-related to the capture and visualization of changes made to a Web service. Visualization and computation of changes can be done in the form of intermediate artifacts Subset WSDL. The insight on the computation of change impact is helpful in testing, top-down development and reduce regression testing. AWSCM is a tool that can identify subset operations in a WSDL file to construct a subset WSDL.