1 - WEB AND ITS TECHNOLOGIES
1.1 the web and its beginnings
The internet may be defined as the worldwide system of interconnected computer and
communication networks that interchange data using the Internet Protocol Suite. This suite is also
known as TCP/IP, from its two most important protocols – the Transmission Control Protocol
(TCP) and the Internet Protocol (IP).
Not to be confused with the internet, the World Wide Web (or www for short) is a system of
interlinked hypertext based documents accessed via the internet. These documents (or web
pages) can be viewed or accessed using a web browser. Besides their content which ranges from
plain text to videos and other multimedia items, the web pages may contain hyperlinks which
identify other documents and facilitate the navigation between different web pages. In a sense,
the internet is the infrastructure of the World Wide Web.
The internet roots can be traced to a project called ARPANET within the Advanced Research
Projects Agency of the US Department of Defense (also known as DARPA – Defense Advanced
Research Projects Agency). (D)ARPA itself was established in 1958 as response to the Soviet
Union launching of the first satellite in 1957. This project grew up from the necessity of
interconnecting in a reliable manner different networking systems and was based on packet
switching . Previously, data communication was based on circuit switching where a dedicated
circuit is used for the communication needs of the entities at the end points of the communication
channel. The first operational instance of ARPANET became operational in october 1969 and
consisted of 4 packet switching nodes, located at
Earlier attempts included
1.2 the nature of web objects
1.3 distributed applications
We detail in this section some of the technical intricacies related to distributed applications.
A distributed application is an application whose execution units lie in different address spaces.
When two people talk to each other in the same room, their communication is direct and
unobstructed. The same paradigm applies when two processes communicate within the same
address space. When the same two people are in different locations communication is done, in
general, using a whole infrastructure, in the most common case, they use cellular phones.
So what is the equivalent of the cell phone for a . The process does not. The stub is the client
side substitute for the real guy (the server). On the other side, the server application does not get
the request from the caller (the client) but from the skeleton. The skeleton is the server side
substitute for the real guy (the client). We see this in the figure from the CORBA section of this
chapter.
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1 - web and its technologies
1.4 corba – bringing objects together
CORBA stands for Common Object Request Broker Architecture and is a standard defined by a
consortium called the Object Management Group (OMG). The clout of this group can be inferred
from both its founding companies (including Hewlett-Packard, IBM, Sun Microsystems, Apple
Computer, American Airlines) and its present day membership structure (over 800 influential
software producing and software consuming companies).
CORBA was supposed to address object interoperability issues, issues derived from two main
sources:
1. the variety of object implementation languages and platforms
2. the distributed character of the applications and objects
Eventually, the objects, in all their variety, will meet on the ORB and will speak the same
language – IDL.
ORB – or Object Request Broker - is a middleware which facilitates the interaction between
applications and distributed objects.
Various ORBs communicate through an abstract protocol called GIOP (General Inter-ORB
Protocol). The GIOP architecture provides the framework for several concrete protocols like:
1. IIOP – the Internet Inter-ORB Protocol is a GIOP implementation to be used over the
internet and provides message passing over the TCP/IP layer.
2. SSLIOP – SSL Inter-ORB Protocol is actually IIOP over SSL, ading authentication and
encryption services.
3. HTIOP – HyperText Inter-ORB Protocol – IIOP over HTTP with transparent proxy
bypassing
IDL stands for Interface Definition Language and describes the interfaces the objects will reveal
to the outside world. The way IDL maps to an actual implementation language like C++, Java,
COBOL, Python or even C is specified by CORBA.
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1 - web and its technologies
A document which provides a detailed view of the CORBA architecture and its components can
be viewed at http://www.cs.wustl.edu/~schmidt/PDF/vinoski.pdf
However, due to the divergent nature of the implementation process of an increasingly complex
specification have lead, in time, to the decline of CORBA as architectural choice in the design and
implementation of enterprise scale applications. The technologies that sustained and inspired
CORBA in its initial stages can now be retrieved in the latest java-centric technologies. In a sense,
the evolution of java and its related technologies have lead to the demise of CORBA
1.5 java
What java brought to the table was:
1. A truly portable object oriented programming language and platform
2. An unsophisticated and almost free development environment
3. A well structured and established class hierarchy
4. A tightly controlled specification.
Despite its inherent drawbacks, like poor performance, java was (is) easy to use and produced
quick results.
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