Tehnologii Web

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.