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A web service is a standardized communication medium between a server and the client on the internet. Being a software module, it performs specific kinds of tasks. In cloud computing, web services are used to provide various functionalities when invoked by a client.
In this article, we introduce the basic concepts surrounding web services:
The figure above shows a typical web service at work. The client computer invokes various calls as requests to the server that hosts the web service.
The process of making requests is called remote procedure calls (RPC). RPC targets the host of a web service and calls specific methods.
An example of a web service is amazon.com, an online store for selling products. The client can be accessing the web service using a .Net or Java user interface, and both of the interfaces can communicate with the web service.
Transfer of data between client and server applications happening in the form of XML (Extensible markup language) documents is the major design concept of web services.
XML is easy to understand just as HTML and many programming languages understand it. It provides a platform of communication for applications developed using different programming languages.
To exchange the XML data between systems or applications, the Simple Object Access Protocol (SOAP) is used. According to Gudgin, the XML document being transferred from a web service to the client is the SOAP message.
This makes it possible for clients written in different languages to exchange data with the web service because a soap message is written in XML.
The evolution of the internet has seen the integration of modern web-based applications into business operations. The applications are written in a variety of programming languages e.g. Java, .Net, Angular JS, Node.js, etc.
This becomes a nightmare for different applications to communicate accurate information. This gave the rise to web services that enable communication between applications built in different programming languages.
There are only two and they include:
For everything to be in place, web services must meet some minimum requirements. This is irrespective of the programming language the application is written. Let us take a look at the individual components:
SOAP is known for transporting XML data in the form of SOAP Messages. It is an independent transport protocol. An XML document follows a specific structural pattern.
The most interesting part of sending SOAP messages and web services is that all happen via HTTP (the standard web protocol).
Elements of a SOAP message
The figure below shows a simple example of SOAP communication
A web service existence must be known before requesting a service. If a service is not found, it cannot be used. The client should further be aware of what the service does to invoke the appropriate web service.
A WSDL document describes the services offered by a web service. This enables a client to find a service and invoke the right method.
Contains the accepted rules for discovering, describing, and publishing web services provided by a specific web service provider. It defines particulars that help in hosting web service information.
In the previous section, we discussed that WSDL contains information about what a web service does. The question remains how a client computer can locate a WSDL file and read the contents.
This is answered by the UDDI, which acts as a database for hosting WSDL files. So the client can access the WSDL file through the UDDI.
The UDDI can be compared to a phonebook directory that contains an individual’s name, contact, address. Similarly, UDDI will have relevant information regarding a web service so that a client can access the WSDL and understand all the operations offered by a server.
In the previous sections, we have discussed why web services came into play in the first place, which is to enable applications written in different programming languages to communicate with each other.
Now let us look at the benefits of using web services:
Each framework has a set of components that work together to get the desired result. Similarly, the following components are present in web service architecture:
Web services have unique features in their behavior as follows:
This section gives more insight into web services using a travel agent scenario. The agent is looking to offer booking capabilities of complete vacation packages: bus tickets, train, plane, hotels, excursions, car hire, etc.
Service providers (hotel chains, bus companies, airlines, etc.) avail web services to clients to make reservations. Financial companies are playing their part to guarantee payments by providing a large number of payment web services and make a coin from each transaction.
The consumer can then make a reservation from a large variety of options available. In this case, the user interacts with machines only in the process of making a booking.
This usage scenario describes how a developer would make the service available and how a user can make a booking of a package.
For this scenario to be practical, some requirements must be met:
For most of such transactions, the WSDL file is in the WSDL primer
Steps a user takes to make flight destination inquiries
Steps for choosing a flight and finding a hotel
Steps to book a flight and hotel
Before the introduction of web services, there was no streamlined exchange of data among the various technologies, business to business (B2B) operations, or vendors.
The evolution of web services has seen interoperability and system integration in the digital landscape. Today, web services provide a platform for less complexity and more functionality.
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