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<HTML><HEAD><TITLE>Chapter 30 -- Incorporating Legacy Systems and Data into an Intranet</TITLE><META></HEAD><BODY TEXT="#000000" BGCOLOR="#FFFFFF" LINK="#0000EE" VLINK="#551A8B" ALINK="#CE2910"><H1><FONT SIZE=6 COLOR=#FF0000>Chapter 30</FONT></H1><H1><FONT SIZE=6 COLOR=#FF0000>Incorporating Legacy Systems andData into an Intranet</FONT></H1><HR><P><CENTER><B><FONT SIZE=5><A NAME="CONTENTS">CONTENTS</A></FONT></B></CENTER><UL><LI><A HREF="#IncorporatingLegacyDataintoanIntranet">Incorporating Legacy Data into an Intranet</A></UL><HR><P>It's rare that an intranet has been built entirely from scratch.Intranet designers usually don't have the luxury of creating alogical computing architecture. Instead, they have to take intoaccount existing corporate computing and networking resources.That means attempting to integrate mainframe-based systems, mini-computer-basedsystems, local area networks, and databases, none of which havebeen designed with an intranet or TCP/IP in mind. Important corporateinformation is stored in a variety of databases that are oftenincompatible-and they have not been integrated into an intranetyet.<P>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 kindsof systems and databases, and because each corporation has designedtheir intranet differently, there's no single solution-and often,no easy solution, either.<P>One solution for those who want to give intranet users accessto legacy databases is to use the Common Gateway Interface (CGI),a technology that gives access to non-Web-based resources suchas databases. CGI scripts-which can be written with a varietyof tools, such as the Perl scripting language and the C++ programminglanguage-send the requests to a database, and then return theresults in an HTML tagged page.<P>That solution works, but has drawbacks. One is that the CGI scriptsare generally written for a very specific situation-a specificWeb page querying a specific database. Often, intranets need greaterflexibility, or have a variety of legacy databases that need tobe accessed. In that case, several technologies can be used. Onethat may prove to be very popular is the use of the StructuredQuery Language (SQL), which is a way of accessing databases. SQLis based on a client/server model. The database acts as a server,and a variety of clients can query the database. With SQL, a databasequery from the Web goes to intermediate software-and possiblyan intermediate server as well-that translates the query intothe SQL language. That SQL query is then sent to the database,which returns the data, which is eventually put into HTML format.<P>Databases aren't the only legacy system that needs to be incorporatedinto an intranet. Others are local area networks (LANs) or theSystems Network Architecture (SNA), a suite of protocols usedto connect IBM mainframe systems. There are a number of ways thatan existing LAN can be incorporated into an intranet. The simplest,of course, is to install TCP/IP technology on all the workstationson the LAN, and to install intranet-based servers, routers, andother similar technologies. However, there may be times when theLAN needs to keep its existing technology. In that instance, bridgescan be used that will allow data to be passed between the intranetand the LAN. Similarly, a TCP/IP to SNA gateway can be used toconnect the mainframe to the intranet.<H2><A NAME="IncorporatingLegacyDataintoanIntranet"><FONT SIZE=5 COLOR=#FF0000>Incorporating Legacy Data into an Intranet</FONT></A></H2><P>One of the biggest problems facing many intranet administratorsis that they must incorporate systems and databases that werecreated 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 varietyof ways. Pictured on this page are some of the possibilities.<OL><LI>One of the most common ways of incorporating legacy systemdata into an intranet is to allow people to search through thelegacy database using the Common Gateway Interface (CGI). CGIscripts can be written so that someone can fill out a form ona Web page, and the script translates the information on the forminto a format that can be understood by the database. The resultsof the query are then delivered back to the Web browser afterthe CGI script has formatted the results with HTML so they arereadable by the Web browser.<LI>One possible way of connecting to a legacy IBM mainframe systemis to enable direct access through the use of tn3270 terminalemulation software, which runs on individual desktop machinesconnected to the company intranet. An SNA gateway sits betweenthe mainframe and the TCP/IP based intranet. The terminal emulationsoftware encapsulates a 3270 data stream in TCP/IP packets. Thegateway strips off the TCP and IP headers and wraps the data inthe appropriate SNA protocol. To the user, it appears as thoughthey are sitting at a dedicated 3270 terminal.<LI>Another choice is to retrieve the most popular data from thelegacy system and place it in static HTML formatted pages on anintranet 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.<LI>As noted above, access via CGI scripts can be problematicbecause they are often written to interact with one specific resourceon the mainframe, such as one specific database. A workaroundsolution is to create a CGI program that takes input from a Webpage 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 froma terminal rather than from a web browser. Terminals can interactwith any resource on the mainframe.<LI>Information sent back by the mainframe computer is markedup with HTML tags and then returned to the Web browser for viewingby the user. The CGI program also adds special buttons to replicatethe many function keys available on a 3270 terminal. This approachis useful because it allows interaction with all resources onthe mainframe through a Web browser.</OL><HR><CENTER><P><A HREF="ch29.htm"><IMG SRC="PC.GIF" BORDER=0 HEIGHT=88 WIDTH=140></A><A HREF="#CONTENTS"><IMG SRC="CC.GIF" BORDER=0 HEIGHT=88 WIDTH=140></A><A HREF="contents.htm"><IMG SRC="HB.GIF" BORDER=0 HEIGHT=88 WIDTH=140></A><A HREF="ch31.htm"><IMG SRC="NC.GIF" BORDER=0 HEIGHT=88 WIDTH=140></A><HR WIDTH="100%"></P></CENTER></BODY></HTML>?? 快捷鍵說明
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