Understanding XML Based Web Protocols
We know that web services are applications or programs which are used to connect and interact with other applications, devices, and systems using web communication protocols. As web services need to be independent of programming languages and underlying operating systems, they use XML based protocols. Here we will discuss some XML based web protocols used by web applications for the communication and interaction with other applications and systems. These are SOAP, WSDL and UDDI.
SOAP stands for Simple Object Access Protocol. It is an XML based protocol which allows applications to communicate via Internet using HTTP. It is better to communicate over HTTP as it is a standard mechanism and supported by all browsers and servers.
SOAP is platform independent and allowed by the firewalls too. SOAP specification specifies how to format message using XML. In fact a SOAP message is an XML message enclosed in a SOAP envelope. SOAP message does not contain any DTD reference and XML processing instruction. It has a header and a body element enclosed in the SOAP envelope. In addition to specify XML format for messages, SOAP specification also defines the mechanism for the representation of program data in XML.
Next is WSDL which stands for Web Services Description Language. It is a language based on XML used for describing, locating and accessing web services. A WSDL document is a simple XML file and has four major elements. These are types, portType, message and binding.
These elements are used for the description of web services in the WSDL document. types represent the data types used in the web service and portType defines the operations performed by the web service. Similarly message and binding represent the messages and communication protocols used by the web service respectively.
portType element is quite important as it defines all the operations that can be performed by the web service and it can be compared to the class libraries in a programming language. There are four operation types defined in WSDL. First are one-way operations where a message can be received but no response is generated.
Second type is of request-response operations where a request can be received and also response is returned. Next are Solicit-response operations which can send a request and then wait for the response. Fourth type of operations is of Notifications which send a message/request like the above one but do not wait for the response.
Now we will understand UDDI. UDDI or Universal Description, Discovery and Integration is a directory or collection of web services. Here businesses can register themselves, search for new businesses or web services, describe web services and store information about them.
UDDI is closely connected with SOAP and WSDL as it communicates via SOAP and it uses interfaces of web services explained by WSDL. The entry in the UDDI directory is marked by an XML file which contains information about the business and its services. UDDI has made possible to search for the appropriate services required for our businesses and it is an efficient mechanism to reach our potential customers and significant markets.
| Generating XML Document Using Java servlet | How to Design a XML Document Easily |Understanding Advanced XML Concepts | Understanding Class Loaders in Java | Understanding The Basic Reasons for Development of XML | Understanding Various Methods of Formatting XML Data | Understanding XML Based Web Protocols | Working With ebXML An Indepth Overview | XML Database Program Knowing the Basic Concepts |