An Introduction to Simple Object Access Protocol
This article has not yet been rated.|
Views (Total / Last 10 Days):
Simple Object Oriented Protocol or SOAP is a simple, light
weight, XML based protocol that can be used for exchange of data in a
de-centralized, distributed environment. It is making headlines these days
within the enterprise development community and promises to revolutionize Web
applications development by facilitating interoperability between heterogeneous
applications. Using the SOAP protocol, objects of any kind, developed on any
platform, using any language can cross communicate with each other. Hence, we
can connect the services offered by different heterogeneous systems together as
components and use these components to build a complex information system with
ease. This article provides a detailed overview of SOAP in a lucid language.
|What is SOAP, Anyway?|
Simple Object Oriented Protocol or SOAP is a stateless, platform
independent, XML based generic lightweight protocol that used HTTP as its
transport and can be used for developing distributed complex computing
environments. SOAP is about applications communicating directly with each
other over the Internet in a very rich way. It is a stateless, message
exchange paradigm that allows for exchange of data between heterogeneous web
applications. SOAP is supported on any platform and be utilized on a wide
variety of applications. SOAP is similar to its contemporary technologies,
like DCOM or CORBA, in the sense that both provide a RPC mechanism for invoking
remote methods. However, SOAP differs from these technologies in the XML Open
Standard that it provides for the purpose of data exchange between homogenous
or heterogeneous distributed applications. SOAP is supported by both HTTP and
SMTP, but HTTP gained more acceptances over the years.
SOAP is platform independent, language independent and
messaging between applications makes this protocol a robust and standardized
mechanism in order to handle message communication across homogenous or
heterogeneous networks. The most common messaging pattern used in SOAP is
Remote Procedure Call or RPC. This indicates that the client sends a request
message to the server. The server in turn sends the response message to the
client. The prerequisite for having a proper understanding of SOAP is XML. This
is because XML is the basis of all SOAP related activities. All SOAP messages
are transmitted in XML format. XML, a platform independent Meta (Language
composed of non-binary ASCII text), has revolutionized the way data is
transferred between systems. XML is fast becoming as ubiquitous as HTTP. It
has now already become an accepted standard for representation and interchange
of data in structured form accross systems. All SOAP messages are transmitted
|Why is SOAP required?|
Distributed Applications that can support heterogeneous
platforms for the purpose of data and information requires a common data format
for transmission of data. We have had protocols earlier like DCOM, RPC, IIOP,
etc, but these were restricted to a homogenous environment only. They have been
around for quite some time now, but they have their own limitations. Any two
systems communicating with each other using any of these protocols should have
support for the protocol that they are using. As an example, if a system "A"
communicates with a system "B" using IIOP, both these systems should
have support for IIOP to ensure that the communication takes place
successfully. For a heterogeneous environment this is not feasible. The
situation is more complex. Simple Object Oriented Protocol (SOAP) is an Open
Standard protocol and the solution to this complexity.
|Advantages of SOAP|
The following are some of the many advantages that SOAP
Simplicity -- The SOAP messages are in simple, human readable XML
Scalability -- This is because it uses HTTP protocol for
Language neutrality -- Can be developed using any language.
Interoperability and Platform Independence-- SOAP can be
implemented in any language and can be executed in any platform.
|Disadvantages of SOAP|
The following are the disadvantages of SOAP.
Slower than CORBA or RMI or IIOP due to the lengthy XML format
that it has to follow and the parsing of the envelop that is required.
It depends on WSDL and does not have any standardized mechanism for
dynamic discovery of the services.
|Composition of SOAP|
As per the SOAP specification, SOAP is typically composed of
the following three parts:
A framework that describes how the message can be constructed and
how it can be processed
A set of encoding rules for exchanging the data types
A convention and a procedure for representing the Remote
|Anatomy of a SOAP Message|
A client sends a SOAP message to the server. This
requesting data is also called a SOAP Request. The server receives the request,
processes the same and sends a response back to the client. This returning data
is known as the SOAP Response. This communication back and forth between the
client and the server takes place through HTTP protocol.
The following constitute a SOAP message declaration:
An envelope element that recognizes then XML file format which
will be sent across as a SOAP message
An optional element that can describes header information
The description of the body which contains the information of the
request and the response elements
Provision for another optional element that provides information as
and when an error occurs
The SOAP format is clearly illustrated in listing 1 that follows.
Listing 1: A SOAP message format
|SOAP support in Microsoft .NET|
This section discusses the support for SOAP that is provided
by the Microsoft .NET Framework. Microsoft .NET provides an excellent inbuilt
support for SOAP. This section discusses the SOAP support that is available in
Microsoft .NET for both Web Services and Remoting technologies.
|SOAP and Web Services|
Simple Object Access Protocol (SOAP), Web Services
Description Language (WSDL), and Universal Description, Discovery and
Integration (UDDI) are emerging as the de facto standards for Web services. A
Web Service can be consumed by any client irrespective of the platform that the
client is using. This is because Web Services are based on the HTTP protocol. The
.NET Framework encapsulates the support for SOAP internally.
|SOAP and Microsoft .NET Remoting|
Unlike Web Services, Remoting is a technology that can be
used in homogenous environments only. Remoting technology uses channels and
formatters. The channels provide the transport protocol and the formatters are
responsible for serialization and de-serialization. We can create SOAP channels
rather than using the HTTP channels in .NET. In such a case, we have to make
use of the System.Runtime.Serialization.Formatters.Soap
namespace in .NET.
It should be noted that SOAP does not address object
activation, marshaling objects/references, garbage collection, etc. Further, as
SOAP is a wire protocol, it does not provide an activation mechanism. However,
we can still use these in our applications as a layer on top of SOAP if
required. This article has provided a detailed discussion on SOAP, why SOAP is
required, the advantages and disadvantages of SOAP and the support for SOAP in
Web Services and Microsoft .NET Remoting technologies.