1. SOAP
SOAP has become almost synonymous with Web services, even though it is just one of many possible bindings for accessing Web services. Besides SOAP. There are other alternative strategies for web services which are
–WSIF (Web Service Invocation framework)
–REST (Representational State Transfer)
What is SOAP?
Few years back, programs were self-contained and did everything they needed to do – get information from the user, manage databases, etc. Then networking became common – the database side was split out and we had client/server systems. The client program still did most of the work, but a database server handled the heavy stuff. Next, the CORBA and COM technologies appeared, allowing us to split the programs into smaller parts – even placing
different parts on different computers. Now, systems are becoming distributed outside the immediate enterprise, across the Internet.When we try and use DCOM or CORBA’s IIOP to talk to objects in other enterprises, however, we find a number of problems. The first is that we usually want to use a TCP port
that is blocked by a firewall. Security administrators are –quite rightly, reluctant about opening ports on their firewalls, and the more enterprises we want to talk to, the more difficult the problem becomes. Even if we succeed and connect to the other enterprise, there’s no guarantee that DCOM will work without further configuration – assuming, of course, that they’re running Microsoft servers. Even different CORBA ORBs often have trouble talking to
each other. What’s needed is a protocol that has a common implementation on all platforms and which can be carried by a commonly used transport. That’s where SOAP comes in.
SOAP is an XML-based messaging protocol. it is a specification, which defines a set of rules for structuring messagesand how to convert an object interface to an XML structure. The resulting XML can be sent to the target object by any transport protocol – such as HTTP or SMTP. Soap is particularly useful for performing RPC-style (Remote Procedure Call) request-response dialogues. It is not tied to any particular transport protocol though HTTP is popular. Nor is it tied to any particular operating system or programming language so theoretically the clients and servers in these dialogues can be running on any platform and written in any language as long as they can formulate and understand SOAP messages. As such it is an important building block for developing distributed applications that exploit functionality published as services over an intranet or the internet. Most firewalls allow external clients to send HTTP packets on port 80 (the standard port for a Web server), so SOAP packets will usually get into the enterprise which is their final destination.
How DOes SOAP Work?
Suppose client object wants to get the information from the server object. It creates a XML object with a reference to the server , interface which will be used , and method used to get results and parameters if it accepts any. Now cliient object will send this XML over http via POST method. Once server object got the XML it will invoke the method of the interface given in XML and populate the results into a xml and send it back to the client object.
A Web service is a piece of business logic, located some where in universe(Internet) that is accessible through standard- based Internet protocols such as HTTP or SMTP.
