Web Services

Learn Web Services

Let us learn about Web Services.

A Web Service is a service available on a network, that will allow other systems to communicate with it, using a defined protocol. The Web part indicates that the service is using transport protocols designed for the World Wide Web, i.e., it uses HTTP to communicate. Other systems can be Web applications, apps in phones and similar.

Firstly, Web Services generally use XML (Extensible Markup Language), which means they are more secure.
Secondly, it is more secure as both Web Services and APIs provide SSL (Secure Socket Layer) during data transmission, but it also provides WSS (Web Services Security).
Thirdly, Web Service is a subset of Web API. For Example, Web Services are based only on three styles of use i.e. SOAP, REST and XML-RPC.
Subsequently, Web Services always need a network to operate.
Lastly, Web Services support “One Code different applications”. This means a more generic code is written across different applications.

APIs come in two main flavours, SOAP and REST. Generally, APIs and Web Services, the two terms have different connotations. However, they technically define the same thing.

“Web Service” is generally used when discussing SOAP-based services. However, API is used in a broader sense, encompassing SOAP, REST, and the rest of the API protocols. Therefore, we simply use the abbreviation API to refer to the service henceforth.

Web Services Components

Important components of the web services. They are,

WSDL – Web Service Description Language
SOAP – Simple Object Access Protocol
UDDI – Universal Description, Discovery and Integration
RDF – Resource Description Framework

WSDL (Web Services Description Language) – A WSDL is a document that should be written using XML. This document describes the following details about the web service:

First of all, the origin of the web service
Secondly, header information
Subsequently, port type
Last but not least, input and output messages

A sample WSDL file

Above all, the role of WSDL is validating web services. This is further done with the help of SoapUI. Moreover, this is only possible with the WSDL document because it configures web services in SoapUI, WSDL. However, if the WSDL document is not valid, SoapUI will throw an exception immediately.

UDDI (Universal Description, Discovery and Integration) – This is a global repository where we can search the web services spread over the globe. Moreover, this is the place where the WSDL is described in detail. In addition, this will communicate through the SOAP protocol which will be explored later in this tutorial.

SOAP (Simple Access Object Protocol) – Generally, it uses XML based data to interact with web applications.

Firstly, SOAP is language and platform-independent as it is written by using XML.
Subsequently, It creates the platform to communicate with the applications that are running in different operating systems using different technologies.
Moreover, most of the Internet applications interact with each other over Remote Procedure Calls that use DCOM (Distributed Component) and CORBA (Common Broker Architecture)
Lastly, these technologies are different than the HTTP.

A sample SOAP document

As you can see, a SOAP document must contain the following elements:

To begin with, envelope element is the topmost tag which identifies the XML document as a SOAP message.
Subsequently, followed by Envelope element, you see the header element that has header information.
Further, the Body element specifies the call and response information.
Lastly, you have a Fault element which contains errors and status information.

RDF

RDF (Resource Description Framework) – RDF contains the description of web resources such as title, author, content, and copyright information. This framework was designed so that computers can be read and understood easily by the web. RDF is completely written by using XML language.

RDF data can be transferred between different types of computers using different operating systems and programming languages. Generally, RDF uses Uniform Resource Identifiers (URIs) on the web and it describes the resources along with the property and property values.

A sample RDF document

<? xml version=”1.0″?>

<RDF>

<author> Wilfred R. Myers </author>

<homepage>http://www. softwaretestinghelp.com</homepage>

</Description>

</RDF>

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