Evolution of Remote Procedure Calls - RPC

A remote procedure call is a request to a server application at another location to perform operations and return information.This is one of very common requirements for any enterprise world.From time to time, there are so many technological advances made on this arena.This article meant for Java evangelists who would like to understand the evolution of RPC with current context.

Remote method invocation - RMI

Enterprise Java Beans - EJB

XML over HTTP - Webservices

XML - RPC

Simple Object Access Protocol-SOAP



Evolution of Remote Procedure Calls - RPC

A remote procedure call is a request to a server application at another location
to perform operations and return information.This is one of very common requirements
for any enterprise world.From time to time, there are so many technological
advances made on this arena.This article meant for Java evangelists who would like
to understand the evolution of RPC with current context.

Microsoft's Distributed Common Object Model - DCOM

Common Object Request Broker Architecture - CORBA

Remote method invocation - RMI

Enterprise Java Beans - EJB


XML over HTTP - Webservices

XML - RPC

XML-RPC is a simple, stable, and well-understood specification. It’s not a
moving target like so many other Web service specifications. It also has
longevity, because the only things that it depends on are technologies such as
HTTP and XML, and basic programming constructs such as arrays, structures, and
scalars. None of those things is going away any time soon. And since everything
related to XML-RPC is freely available and downloadable, you can have a Web
service up and running in a single afternoon.

Simple Object Access Protocol-SOAP

XML-RPC is a simple protocol that
allows software running in different environments to make remote procedure calls
over the Internet. XML-RPC uses two industry standards: XML (extensible markup
language) for encoding messages, and HTTP (hypertext transfer protocol) for
transporting them. A properly formatted XML-RPC message is an HTTP POST request
whose body is in XML. The specified remote server executes the requested call
and returns any requested data in XML format.

XML-RPC recognizes procedure parameters by position. Parameters and return
values can be simple types such as numbers, strings, and dates, or more complex
types such as structures and arrays. To learn more about XML-RPC messages, see
the XML-RPC specification at http://www.xmlrpc.com/spec.

SOAP (Simple Object Access Protocol) is an RPC protocol designed for a
distributed environment, where a server may consist of a hierarchy of objects
whose methods can be called over the Internet. A goal of SOAP is to establish a
standard protocol that will serve both web service providers and service users.
As with other remote procedure call protocols, SOAP uses XML to encode messages
and HTTP to transport them. A SOAP request contains a header and an envelope;
the envelope in turn contains the body of the request.

One key difference between the SOAP and XML-RPC protocols is that with SOAP,
parameters are notational (a request must encode the method parameter names
within its XML), rather than positional (recognized by position). To learn more
about SOAP messages, see the SOAP specification at http://www.w3.org/TR/.

Remote procedure calls provide a powerful tool for accessing services over the
Internet. For example, there are already a variety of web-based servers that can
check spelling, translate text between languages, provide stock prices, supply
weather and traffic information, and more. You can find available services at
sites such as XMethods at http://www.xmethods.net/. There you can also find
information you’ll need to make remote procedure calls to these services.





The biggest conceptual difference between SOAP and XML-RPC is that XML-RPC
exchanges a limited number of parameters of six fixed types, plus structs and
arrays. However, SOAP allows you to send the server arbitrary XML elements. This
is a much more flexible approach.


Remote procedure call systems have been around since around 1984 when they were
first proposed (A.D. Birrell and B.J. Nelson, 1984). During the intervening 15
years, numerous evolutionary improvements have occurred in the basic RPC system,
leading to improved systems-such as NCS (T.H. Dineen et al., 1987)-that offer
programmers more functionality or greater simplicity. The Common Object Request
Broker Architecture from the Object Management Group and Microsoft's Distributed
Common Object Model are this evolutionary process's latest outgrowths. With the
introduction of Java Developer's Kit release 1.1, a third alternative for
creating distributed applications has emerged. The Java Remote Method Invocation
system has many of the same features of other RPC systems, letting an object
running in one Java virtual machine make a method call on an object running in
another, perhaps on a different physical machine. On the surface, the RMI system
is just another RPC mechanism, much like Corba and DCOM. But on closer
inspection, RMI represents a very different evolutionary progression, one that
results in a system that differs not just in detail but in the very set of
assumptions made about the distributed systems in which it operates. These
differences lead to differences in the programming model, capabilities, and the
way the mechanisms interact with the code that implements and built the
distributed systems