Re: Design question - layered approach

Booth,

It depends :)

The whole point of designing is to determine the answers to those questions.

For a nice intro, check out the April 2009 issue of System i News,
Scott, Paul Tuohy, Tony Cairns, and Don Denoncourt teamed up for a set
of articles which demostraite an RPG business layer with a 5250, PHP,
Groovy/Java, and CGIDEV2 front end.
http://systeminetwork.com/article/rpg-and-web-technologies-get-there
http://systeminetwork.com/article/rpg-web-cgidev2-way
http://systeminetwork.com/article/rpg-web-php-way
http://systeminetwork.com/article/rpg-web-java-or-groovy-way

Also check out:
http://systeminetwork.com/article/writing-reusable-service-programs

HTH,
Charles


On Tue, Sep 8, 2009 at 11:33 AM, Booth Martin<booth@xxxxxxxxxxxx> wrote:

This seemed simple enough on the face of it, and then of course it
slipped away.

A case has been made for dividing the pieces of an application into, as
I understand it, at least three layers.

The first layer is the data and it's constraints and security.
The second is the layer for business rules.
The third is the top layer, for the user interface, allowing several
different UI solutions to co-exist  at the same time.

That all makes sense to me.

Two problems are confusing me.  The second one is: what mechanism does
one use to arrange the data for the mating of the UI layer to the
business rules layer?    The business rules program, as I understand the
design, has to not know or care whether the user interface is RPG, Java,
or whatever.  What, specifically, does the business rules program expect
to get & send from & to the UI?

Here's a simple example:  A data file with 2 key fields and a 480-char
data field.  The UI needs to display the key fields and also a single
record.  Add/update/delete are possible when the single record is displayed.

(Maybe this is all too simple for layering, but I sooner expect that I
don't really understand the process itself.)
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