Web services overview

The term web service is either

• (generic) a service offered by an electronic device to another electronic device, communicating with each other via the World Wide Web, or
• (specific) a web service implemented in the particular technology or brand, W3C Web Services.

In a web service, the Web technology such as HTTP—originally designed for human-to-machine communication—is utilized for machine-to-machine communication, more specifically 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 Wikipedia's 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.

Explanation[edit]

Web services architecture: the service provider sends a WSDL file to UDDI. The service requester contacts UDDI to find out who is the provider for the data it needs, and then it contacts the service provider using the SOAP protocol. The service provider validates the service request and sends structured data in an XML file, using the SOAP protocol. This XML file would be validated again by the service requester using an XSD file.

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.^{[citation needed]} 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 doesn't 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.
• Which specific parameters are needed in the data request.
• What would be the structure of the data produced. (Normally, data is exchanged in XML files, and the structure of the XML file is validated against an .xsd file.)
• What error messages to display when a certain rule for communication is not observed, to make troubleshooting easier.

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 which do not rely on strict rules.^[4])

A directory called UDDI (Universal Description, Discovery and Integration) 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 system it can contact for receiving that data. Once the software system finds out which other system 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.

Interview questions on web services. What is interoperability in web services? Explain web service protocol stack layers Explain web service architecture with diagram What is UDDI? What tools are used to test web services? What are different types of web services? What are the elements of soap message? What is wsdl in web services? What is difference between top down and bottom up approach in soap web services? Explain contract first approach in web service Explain contract last approach in web service What is a resource in restful web services? What are the http methods used in restful web services? What are different ways to test web services? Can we maintain user session in web services? How to choose between soap and rest web services? Explain annotations used in jax-ws api How to get wsdl file of a soap web service? What is JAX-RS API? Explain some implementations of jax-rs api What are the annotations used in JAX-RS API?