RE: Application design

["Joe Pluta" <joepluta@xxxxxxxxxxxxxxxxx>]

> From: Booth Martin
>
>  Right.  Good idea.  Lets see an example Joe.  Perhaps a simple
> example:adding an address to a person's name. They live in Quebec, Canada
> and have provided "Qu" as their province.  (Quebec is usually "PQ")
>
> We don't need real code, but what does get done where?

This actually kind of a cool example.  Let's say that you start out with a
standard customer file, with a customer name, address and all that jazz.
You might define a business entity to be "Address", which contains a bunch
of attributes, including street address, state/province, postal code, and so
on.

Your code is simple:

        GetAddress(customer)

In this simple environment, this will return a data structure containing the
information from the customer master.  Now, however, you decide to increase
your capabilities a little bit, and you add ship-to addresses.  You can
split off the address information into a separate file, add a *NOPASS
parameter to your GetAddress, and suddenly you've created the following:

        GetAddress(customer) returns the corporate address
        GetAddress(customer : shipto) returns ship-to address

This is starting to get interesting!  Now let's say you decide to have a
generic lookup scheme, where you store all addresses in a file, with a type
and a generic key.  You add a new procedure:

        GetTypedAddress(type : key1 : key2)

Now, you say, the old GetAddress is broken.  Not so!  You simply subsume the
code into the GetTypedAddress, and then modify the GetAddress as follows:

        GetAddress(customer : shipto)
        return GetTypedAddress('C' : customer : shipto)

Pretty cool, eh?  Not only that, the GetTypedAddress can be smart enough to
access your database for local information, but if it recognizes that the
information is not locally available it can get it smoe other way,
transparently to the application.  For example, let's say it's a ship-to
address from a client - GetTypedAddress might invoke a web service on the
client box to get the info.

This level of abstraction is very powerful when done correctly.

Joe