All Categories :
Intranets
Chapter 30
Incorporating Legacy Systems and
Data into an Intranet
CONTENTS
It's rare that an intranet has been built entirely from scratch.
Intranet designers usually don't have the luxury of creating a
logical computing architecture. Instead, they have to take into
account existing corporate computing and networking resources.
That means attempting to integrate mainframe-based systems, mini-computer-based
systems, local area networks, and databases, none of which have
been designed with an intranet or TCP/IP in mind. Important corporate
information is stored in a variety of databases that are often
incompatible-and they have not been integrated into an intranet
yet.
That presents a major problem to anyone designing an intranet:
how to incorporate all these incompatible systems into their design.
As you might imagine, because there are so many different kinds
of systems and databases, and because each corporation has designed
their intranet differently, there's no single solution-and often,
no easy solution, either.
One solution for those who want to give intranet users access
to legacy databases is to use the Common Gateway Interface (CGI),
a technology that gives access to non-Web-based resources such
as databases. CGI scripts-which can be written with a variety
of tools, such as the Perl scripting language and the C++ programming
language-send the requests to a database, and then return the
results in an HTML tagged page.
That solution works, but has drawbacks. One is that the CGI scripts
are generally written for a very specific situation-a specific
Web page querying a specific database. Often, intranets need greater
flexibility, or have a variety of legacy databases that need to
be accessed. In that case, several technologies can be used. One
that may prove to be very popular is the use of the Structured
Query Language (SQL), which is a way of accessing databases. SQL
is based on a client/server model. The database acts as a server,
and a variety of clients can query the database. With SQL, a database
query from the Web goes to intermediate software-and possibly
an intermediate server as well-that translates the query into
the SQL language. That SQL query is then sent to the database,
which returns the data, which is eventually put into HTML format.
Databases aren't the only legacy system that needs to be incorporated
into an intranet. Others are local area networks (LANs) or the
Systems Network Architecture (SNA), a suite of protocols used
to connect IBM mainframe systems. There are a number of ways that
an existing LAN can be incorporated into an intranet. The simplest,
of course, is to install TCP/IP technology on all the workstations
on the LAN, and to install intranet-based servers, routers, and
other similar technologies. However, there may be times when the
LAN needs to keep its existing technology. In that instance, bridges
can be used that will allow data to be passed between the intranet
and the LAN. Similarly, a TCP/IP to SNA gateway can be used to
connect the mainframe to the intranet.
One of the biggest problems facing many intranet administrators
is that they must incorporate systems and databases that were
created without TCP/IP in mind-what are called legacy systems.
These systems and databases may be mainframe-based, minicomputer-based,
or LAN-based. They can be incorporated into an intranet in a variety
of ways. Pictured on this page are some of the possibilities.
- One of the most common ways of incorporating legacy system
data into an intranet is to allow people to search through the
legacy database using the Common Gateway Interface (CGI). CGI
scripts can be written so that someone can fill out a form on
a Web page, and the script translates the information on the form
into a format that can be understood by the database. The results
of the query are then delivered back to the Web browser after
the CGI script has formatted the results with HTML so they are
readable by the Web browser.
- One possible way of connecting to a legacy IBM mainframe system
is to enable direct access through the use of tn3270 terminal
emulation software, which runs on individual desktop machines
connected to the company intranet. An SNA gateway sits between
the mainframe and the TCP/IP based intranet. The terminal emulation
software encapsulates a 3270 data stream in TCP/IP packets. The
gateway strips off the TCP and IP headers and wraps the data in
the appropriate SNA protocol. To the user, it appears as though
they are sitting at a dedicated 3270 terminal.
- Another choice is to retrieve the most popular data from the
legacy system and place it in static HTML formatted pages on an
intranet Web server. When an individual wants the information,
they simply type in the URL for the static page and retrieve it.
This solution works fine for information that is static, meaning
not frequently updated, such as quarterly financial reports.
However, it will not work for information that is frequently updated.
- As noted above, access via CGI scripts can be problematic
because they are often written to interact with one specific resource
on the mainframe, such as one specific database. A workaround
solution is to create a CGI program that takes input from a Web
page form and translates it into the language used by a 3270 terminal.
The translated data stream is then sent on to the mainframe computer.
To the mainframe, the incoming information appears to come from
a terminal rather than from a web browser. Terminals can interact
with any resource on the mainframe.
- Information sent back by the mainframe computer is marked
up with HTML tags and then returned to the Web browser for viewing
by the user. The CGI program also adds special buttons to replicate
the many function keys available on a 3270 terminal. This approach
is useful because it allows interaction with all resources on
the mainframe through a Web browser.
Contact
reference@developer.com with questions or comments.
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EarthWeb Inc., All rights reserved.
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Copyright 1998 Macmillan Computer Publishing. All rights reserved.
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