What is Web Service?

Web service is an XML-based information exchange system that uses internet for a direct application-to-application.

We will be discussing what is web service in detail along with how it works, its components and advantages.

Table of Contents

• What is web service?
• At a glance
• Working
• Features
• Components
• Advantages

What is web service?

Web service refers to a  service offered by an electromagnetic device to another device. These devices communicate with each other through the internet. It can be any type or piece of software that uses a standardised XML messaging system and is available on the internet. In other words, it can be referred to as a server that runs on a computer device.

It listens to requests at a specific port over a network that serves web documents such as XML, JSON and HTTP images. This can be a self-contained, distributed, modular and dynamic application. It can be described, provoked, invoked, located or published over any network for creating processes and products. Itmay be local, web-based or distributed.

Web Service in a Glance

You must have now gained a basic understanding of web services, let us discuss some of its features. 

• Collection of open protocols and standards to exchange data between systems and applications.
• Available on both the internet and intranet.
• It can be used over any operating system and programming language.
• Discoverable using a simple find mechanism.
• Self-describing via common XML grammar.
• Uses HTTP for transferring machine-readable file formats such as JSON and XML.
• In case a web service is not found, it cannot be used. This is why a client invoking the service must be aware of its location.

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Working of Web Services

A web service uses open standards such as WSDL, HTML, XML, and SOAP. By using these open standards, communication can be enabled among different applications. It uses XML for tagging data, and WSDL for transferring the availability of services. SOAP is used for transferring messages.

To understand this, let us consider an example. Suppose there is a simple system and its processing logic is written in Java while it resides on the Solaris machine. It also interacts with the database for storing information. Let us take a look at the stepwise process:

• The client program will bundle the account information into a SOAP message.
• Now, this SOAP message will be sent to the web service in the form of a body of an HTTP post request.
• The web service will unpack the SOAP request and will convert it into a command that is understandable by the application.
• The application will process the information as needed. It will then respond with a unique account for the customer.
• Web service will package the response into other SOAP messages. It sends this response back to the client as a response to the HTTP request.
• Client program then unpacks the SOAP message for obtaining the results of the account registration process.

Features of a Web Service

The following features are indicative of a web service:

• The UI of a web service provider can change over time without affecting the ability of the user to interact with the service provider.
• It has a loosely coupled architecture. This means that there is a much easier integration between different structures.
• Web services can be both asynchronous and synchronous. Asynchronous operations allow clients to involve a task and then, carry on other tasks. Before continuing in synchronous invocations, the client is blocked. The client, then, has to wait for the web service to complete its operation.

Components

Almost every service uses the following components:

1. Simple Object Access Protocol (SOAP)

This refers to a transport independent messaging protocol that is built on sending XML data in SOAP messages form. To every message, an XML document is attached. Here the structure of the XML document follows a pattern. Everything is sent via HTTP in the case of SOAP and web services. In every SOAP element, a root element (which is the first element in an XML document) is required.

2. Universal Description, Discovery, and Integration (UDDI)

It refers to a standard to specify, publish and discover online services of a service provider. It helps in hosting data via web services using certain specifications. UDDI is a repository for storing WSDL files. It serves as a database for WSDL files. Due to this reason, client applications have complete access to UDDI. The aim of storing the files here is that the client application can discover a WSDL file to learn about the actions offered by a web service.

3. Web Services Description Language (WSDL)

WSDL is an XML based file that helps in understanding what web services do to a client application. It provides client applications with the ability to locate a service. The client application can also understand the method to use a web service using a WSDL document.

Advantages of Web Services

Web services have the following advantages:

1. It is a controlled code component that delivers its functionality to end-users. This capability can be accessed over HTTP protocol. It means it is accessible from anywhere across the internet. Web services are valuable since all apps are now accessible via the Internet. Regardless of being located anywhere, it can provide the required functionality.
2. Since web services employ SOAP over HTTP protocol, they allow using existing low-cost internet connections for their implementation. Web services can be developed using additional dependable transport protocols, such as FTP, in addition to SOAP over HTTP.
3. A single web service can be simultaneously used by several client applications.