what exactly is a legacy system?

[venu patlori]

hi! can anybody tell me,what exactly is a leagacy application or a legacy system,and where could it be in a 3-tier Architecture.
replies highly appreciated.
thank's in advance venu.

[Matt Midcap]

Hi venu,
I'm going to move this to the "Java in General" forum ( http://www.javaranch.com/cgi-bin/ubb/forumdisplay.cgi?action=topics&forum=Java+in+General+(beginner)&number=33&DaysPrune=1000&LastLogin= )where you might get a more stimulating discussion on this topic.
Best Regards,
Matt

[Shama Khan]

I'll give it a shot. Legacy systems are the mainframe oriented systems - not networked but using dumb terminals.
An example would be a DB2 database located on a vax machine with the interfacing application being on the mainframe and accessable only by a dumb terminal.
A 3 tier architecture could still be built around a legacy system where your servlet/jsp oriented web application located on a server can be making calls to a database located in a vax environment and the application being accessable by a client via the internet or a virtual private network.
Most companies (at least the big and long established ones) still have legacy systems as part of their multi-tier architecture.
I hope that helps a bit.
Shama
[This message has been edited by Shama Khan (edited February 05, 2001).]

[Cindy Glass]

For instance we have several systems that have java gui's and use RMI to call servlets that run and get the data from mainframe DB2 databases. These databases are so HUGH that there is NO WAY you would want to try anything but a mainframe, but we still want the nice GUI front ends. Slowly we are replacing lots of mainframe screens with Java.
Actually I think the term Legacy relates to more than just mainframe systems. It is any of the older procedural non-internet type applications. Technically an old DOS game is a Legacy application because it is so old that it does not work well with todays technology.

[Grant Crofton]

A legacy system is something that should be avoided at all costs.

[Cindy Glass]

Well now Grant, that is a controversial comment.
Mainframes are here to stay, for a reason. They can handle the vast amount of data that major corporations need to manipulate better than any existing Lan based databases. (I know for while there was hype about mainframes dying, but believe me- won't happen this generation). And existing legacy systems are going to be around for a LONG time. Granted that the old COBOL PL/I type of maintainance of the Legacy data is out of date, but they will still be here for the next 10 - 20 years anyway, because it is too expensive and complicated to replace them all.
Of course it is more FUN learning the new stuff like Java, but if you want more chances at a good job it would be good to be familiar with some of that legacy stuff.
And if you want to build new stuff, it is good to be able to interact with all that existing powerfull stuff already in place.
So I guess it depends on what you mean when you say "avoid a legacy system". Avoid their existance? Avoid their data? Avoid their old maintanance code?

[venu patlori]

Thank's a lot shama and cindy,for elobarating so nicely on legacy systems.yes i agree with cindy that legacy systems cannot be ignored atleast for the time being,as replacing these systems would be very costly.
Thank's a lot
venu