SOAP is an XML-based messaging protocol specification for exchanging highly structured data in the transfer of internet applications in various computer networks. It is used to exchange messages of various types, which may include application messages, error messages, time messages, security messages, group messages, and non-network messages. All messages are exchanged between the application and the transport layer on the internet.
SOAP was originally developed by J. Philippe Ouellette in 1993. Later, other involved parties added their contributions to it. The result is quite impressive, with extensive support for various data types and advanced messaging capabilities. Many web servers use SOAP to allow fast application response times. SOAP was partially based on the XML message format. XML is very simple markup language, and the SOAP specification has some complex Soap .
XML is well known as a flexible, standardized format for representing and exchanging data. In fact, XML was developed to solve certain shortcomings in earlier technologies like Hypertext Preprocessor (HTML), and to provide a more convenient format for representing documents. Before XML, various protocols had to be used to represent data. These protocols include HTTP, SMTP, TCP/IP, and SOAP.
The major part of the Soap object is the so-called SOAP resource. A SOAP resource consists of a standard body and a number of generic messages. Messages of types SOAP_MAXLEN and SOAP_MESSAGE are present, which define the maximum length of a message that can be received. There is also a standard method to send a message, which is built-in to every Soap server.
The SOAP protocol defines a couple of abstraction layers, which allow easy development of custom client and server applications. The first layer is the application programming interface or APR. This layer controls the behavior of all internal Soap objects. The second layer is called the middleware. It helps the client Soap application to interact with an HTTP web service, using a standardized message format.
XML messaging is widely used to communicate with external Soap resources. The advantage of XML over other popular methods of Soap programming is that XML is not subject to fashion trends and does not need to conform to a specific format. XML messaging can be used to exchange information between Soap servers and web services. XML message formats can be easily transformed into SOAP messages. XML messaging also allows easy distribution of Soap resources.
Web services are one of the most important features of Soap technology. A WSDL based client application can access a variety of interactive Soap elements. Some popular web services are XPath, J Blaz and xml helpers. A WSDL browser is required to run Soap applications. A WSDL browser works by browsing a web services layer instead of a traditional web browser. A WSDL browser is not necessary for the execution of all Soap technologies, as the underlying Soap server can send HTTP requests directly to Soap resources.
The Soap programming language includes support for several other protocols, including the following: Simple Object Access Protocol (SOAP), RDF/EDML, TIES, HTTP, SMTP and XML. A complete Soap application can represent a wide variety of data structures, including arrays, lists, dictionaries and schemas. A WSDL browser is necessary for the execution of Soap applications on a WSDL enabled computer. This is because a WSDL browser can access resources not supported by a non-WSDL browser.
The SOAP specification defines the correspondence between the SOAP messages and the XML message types. The XML message resource can be defined by the XML syntax or by the partial syntax. A WSDL browser can access these resources without requiring the use of XML syntax. However, it should be noted that partial syntax is more complex and usually not supported by all browsers.
The SOAP specification defines four general transports of SOAP messages: Internet transport (a) - this message is used to communicate with remote devices over a network; XML transport - this message is used over XML networks; RTC - This is a transport protocol independent of any other SOAP protocol; RTC transactions - in case of real-time transactions the SOAP transaction protocol is implemented within the RTC software. Web services are an area of high growth and controversy, as many businesses are apprehensive to apply this type of software in their systems due to the security issues. To solve these security problems SOAP has been designed with security as a top priority. SOAP security includes the use of opaque transports and secret containers and provides functionality similar to Java's security properties. This feature makes SOAP secure as it prevents a client from determining the type of the server, browser, device etc., from which a SOAP application is trying to access.
There are many aspects of SOAP architecture that are similar to the XML specification. For example, both SOAP applications and XML documents can contain "namespaces". However, the XML architecture makes it possible to maintain cross-reference information within a single hierarchy as opposed to the SOAP document hierarchy. Furthermore, both SOAP languages and XML can support the concept of schemas and data types, although the SOAP message format does not.