Explain different types of web services in cloud computing.

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Different types of Web Services are:- 

1. XML-RPC (Remote Procedure Call) 

2. UDDI

3. SOAP

4. WSDL

5. REST



 1. XML-RPC (Remote Procedure Call) 

XML-RPC (Remote Procedure Call) is the most fundamental XML protocol for exchanging data across a wide range of network devices, which allows applications to invoke functions or procedures across a network. XML-RPC performs RPCs using XML messages. In the XML request, the XML-RPC client gives a Procedure name and arguments, and the server delivers either a fault or a response in the XML response. The body of the HTTP response contains the network. This platform-independent web service uses HTTP to transmit data and communicate other information from the client to the server in a timely and efficient manner. The body of the HTTP response contains XML replies. XML-RPC enables the communication between many programs so that a Java client application can communicate with a Perl server application.




2. UDDI

UDDI (Universal Description, Discovery, and Integration) is an XML-based standard used to describe, publish, and discover web services. UDDI is a specification for a distributed web service registry, which is a platform-independent and open framework. It essentially serves as an online register for firms all across the world. The major purpose is to improve the efficiency of digital transactions and e-commerce across enterprise platforms.UDDI communicates via SOAP, CORBA, and the Java RMI Protocol and uses WSDL to describe web service interfaces. UDDI is regarded as one of the three foundation standards of web services, along with SOAP and WSDL. UDDI is divided into two parts:

  1. A registration containing all a web service's metadata, including a link to the service's WSDL description.
  2. A collection of WSDL port type definitions for altering and querying the register.

A UDDI registry may be used by any firm to store three categories of information. These are as follows: 

White Pages: White pages contain basic information on the company and its operations such as the name of the firm, address, phone number, and basic information about the firm. 

Yellow Pages: Yellow pages contain more information about the firm, such as the types of electronic capabilities that the firm provides to anybody who wants to do business with it. It accepts corporations based on their industry type, product codes, business identity codes, and industry code, making it easier for businesses to navigate through the listings and get precisely what they are looking for.

Green Pages: Green pages contain technical details about a web service. It allows someone to bind to a Web service after it has been found. It includes various interfaces, URLs, discovery information, and similar data required to find and run the Web service. 

The technical architecture of UDDI comprises three parts:

The UDDI Data Model (Schema) 

UDDI API Specification

UDDI Cloud Services

The UDDI Business Registry (UBR) is the Public Cloud, which is conceptually a single system composed of several nodes whose data is synchronized through replication. The present cloud services provide a directory that is conceptually centralized but physically dispersed. It implies that data provided to one root node is immediately duplicated to all other root nodes. At the moment, data replication happens every 24 hours. Microsoft and IBM presently provide UDDI cloud services.


3. SOAP

SOAP which stands for Simple Object Access Protocol, is a W3C standard, XML-based Web service protocol for exchanging structured data and documents through HTTP or SMTP (Simple Mail Transfer Protocol).

As it is language-independent, it enables separate programs running on different platforms to Communicate using XML. It is a platform-independent format for sending messages. SOAP also uses a web service description model using WSDL (Web Services Description Language) documents. This defines the appearance of SOAP requests (client-side) and responses (server-side). SOAP web services also include Security and addressing requirements.

As illustrated in the figure 8.7, the web services provided by the service provider are described using WSDL (Web Services Description Language) and registered in the UDDI (Universal Description, Discovery, and Integration) registry, which contains all of the information required to identify the web service. After a requestor has queried the UDDI registry and identified the needed service, the WSDL file for that service may be retrieved from the registry and consumed via SOAP message.

Advantages

  • Usually easier to consume,
  • More standards are available (such as WSDL) Distributed computing

Disadvantages

  • Difficult set-up
  • Complicated coding


4. WSDL

WSDL, which is an abbreviation for Web Services Description Language is an XML-based language for defining web services and how to access them. WSDL, which is developed collaboratively by Microsoft and IBM is pronounced 'wiz-dull' and written as 'W-S-D-L. This XML-based protocol is used for exchanging information in decentralized and distributed systems that are also the standard format for describing a web service. The specification of WSDL explains the mechanisms to access a web service and the actions that will be performed so, WSDL is used to describe how to interact with XML-based services. WSDL is a component of UDDI, an XML-based global business registry.


5. REST

REST, which is short for Representational State Transfer, is an architectural paradigm in which each unique URL represents a distinct object of some type. REST allows communication and connections between devices and the Internet for API-based operations. A REST web service communicates through HTTP and supports various HTTP methods, including GET, POST, PUT, and DELETE. It also provides basic CRUD functions. The original RESTful architecture was established by Roy Fielding,one of the key authors of HTTP.

Advantages

  • Lightweight
  • Human readable Easier to build

Disadvantages

  • Point-to-point communication, 
  • Lack of standards

Think about a simple account management and order processing system. The accounting personnel uses a client application built with JSP to create new accounts and enter new customer orders. The processing logic for this system is written in Java and resides on a Solaris machine, which also interacts with a database to store information. 


The steps to perform this operation are as follows:

  • The client program bundles the account registration information into a SOAP message.
  • This SOAP message is sent to the web service as the body of an HTTP POST request. 
  • The web service unpacks the SOAP request and converts it into a command that the application can understand.
  • The application processes the information as required and responds with a new unique account number for that customer. 
  • Next, the web service packages the response into another SOAP message, which it sends back to the client program in response to its HTTP request.
  • The client program unpacks the SOAP message to obtain the results of the account registration process. 

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