General talk about software patterns

["Prabodh Saha" <prabodhs AT ivycomptech.com>]

Hi Sourav,
        Let me first state what I did understand from your mail.

        a) U want to access data from your backend database.

        b) There are (say) three different backend DB's

        c) There are (say) three different applications one for each DB

        d) These three appications (lets call A,B,C) talk to each other (via 
msgs),
           when need others' data or for some other business reasons.

        e) Now if Application A wants to access the data from DB of 
Application C,
           in normal case it will request application C by sending msg
                but
           in some specific situations, it may directly talk the DB of C and 
pick
data

............................................................................
...

        If that is the case, I think the "Policy" pattern will help you.

        Each of your application should have a policy object (singleton for 
each
appln),
      which will support the direct connectivity to the "OTHER" DB's.
        If you want, you can have the flexibility of loading this policy in 
run
time.

        On the specific optimizing occassions (which you may detect during run
time)
      your application will call concerned methods on its "policy object"
        to gather a specific data from a specific DB. The policy 
implementation can
be
        done in number of ways like:

                a) Have different methods for each kind of data for each kind 
of DB

                b) Have generic methods in the Policy object, which will take 
your
                   desired data and conatiner DB's name / url as argument

                c) For both of the above cases, the Policy can take config 
params
                   from a flat file - optionally read periodically

        If you need any kind of elaboration, please revert

Regards,
Prabodh


-----Original Message-----
From: 
patterns-discussion-admin AT cs.uiuc.edu
[mailto:patterns-discussion-admin AT cs.uiuc.edu]On
 Behalf Of souravm
Sent: Tuesday, June 22, 2004 10:05 AM
To: 
patterns-discussion AT cs.uiuc.edu
Subject: [patterns-discussion] Any Data access pattern for accessing
data across subsystems ?


Hi All,

I'm looking for a design pattern for accessing data across multiple
subsystems.

To elaborate -

1. Let us assume that there are 3 functionally independent subsystems in
a system being designed.
2. The interaction happens between these subsystems through messages at
the business layer of each subsystem.
In this way no subsystem accesses the table(s) of other subsystem
directly.
3. However, for performance optimization, it might be needed that for
certain cases one subsystem need to access tables of other subsystems
through JOINs.

In this situation I'll like to know if there is any specific pattern
used for implementing a performance trade off described in point 3 ?

My aim is to achieve the above mentioned performance goal as well as
retaining the modularity of the subsystems as much as possible.

Any pointer/insight/information will be really appreciated.

Regards,
Sourav


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