Re: legacy to 3 tier

[Pluta@xxxxxxxxxxxxxxxxxx]

We are looking at some old legacy COBOL code to be converted to 3 tier
architecture.
Separating the presentation layer into Java, processing in COBOL and common
database access
routines.
Can anyone throw some light on the approach that one should take,
methodology etc,.
--------------

Rajan, this is exactly what I've been working on for the past couple of
years.  While I do most of my work with RPG legacy systems, the same idea
applies to COBOL.

To me, the idea is to be able to do your changes gradually, with a minimum
of disruption for the end users.  To do that, you want to switch to a
graphical user interface as quickly as possible, and then let them get
comfortable with it while you begin the much more difficult work of
separating application control and business logic.

Replacing the user interface with an object-oriented approach is very easy.
You simply modify your programs to call an API rather than write to a
display file.  The API sends data to a display file emulation object.
Then, when you're ready to read a reponse, the object displays its data to
the end user in whichever format you desire (my architecture supports thick
Swing client and thin JSP clients).

Once you've done this, your users have their graphical interface and you
can begin the much harder work of separation.  The bad news is that
converting from traditional monolithic "spaghetti" code to something more
object-oriented is not easy.  The good news, of course, is that you can
test the programs using the new user interface objects, and once they are
finished you can put them into production and the users won't even realize
it.

Next, you can start converting your file serves into actual objects; as you
succeed in this, it means your servers can migrate to other platforms if
necessary.  Once all that is done, you can begin to think about distributed
architectures, such as RMI.

I've got a working example of the first phase (I call it revitalization) on
my website.  Go to:

http://www.zappie.net/revitalization

Unfortunately, my solution is focused on RPG, but it should work just as
well for COBOL.

Joe Pluta
www.java400.net
www.zappie.net


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