To learn any technology based on web service it is essential to learn the following topics in details to gain proper understanding.
Interoperability
Interoperability means the ability to communicate with other technology or language with ease. In object oriented programming we can design components which can be reused in the same technology or language. For instance Java Beans can be consumed in any Java application, but what about consuming these Java Beans in.Net? Interoperability solves this problem by providing loosely coupled architecture between diverse applications to communicate with one another. To have interoperability there must be some interface or common standards between the applications to communicate with each other. As shown in Figure 1, an application developed in JAVA is able to consume the functionality available in .NET application (regardless of the language such as C#, VB etc.) with ease. So it is possible because the systems are interoperable. Now how to provide interoperability? It is possible due to web service. So in the following section we will learn about web service and underlying concepts related to it.
Figure 1. Communication between .NET and Java
Web Service
A web service is a method of communication between two electronic devices over the World Wide Web. A web service is a software function provided at a network address over the web or the cloud, it is a service that is “always on” as in the concept of utility computing. The W3C (W3C Website) defines a “Web service” as:
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 (Haas, 2004).
A Web Service can be developed in different languages such as C#. Net, JAVA or other programming languages. A .NET web service can be developed by using Microsoft Visual Studio 2010. Similarly a web service can be developed in JAVA using IDEs such as NetBeans or Eclipse. Once a web service is developed in any language it can be consumed in any other language without knowing more details about the web service. It is the pillar to provide interoperability between diverse systems. The client application needs to know the WSDL file only. Now questions arise that how diverse system communicate with each other as they are not having common data types. For instance, in C# .NET to store integer data, Int16, Int32, Int64 are available while in Java Integer wrapper class is available and in PHP no data types are available as it is a loosely typed language. So communication between these data types, concepts of serialization is used which is explained below.