Re: Definitions
From: Universe (universe_at_covad.net)
Date: 10/21/03
- Next message: Steve: "Re: Basic books on OOA&D"
- Previous message: Dave Benjamin: "Re: OOD Refactoring RDMS Newbie!"
- In reply to: rackri: "Definitions"
- Next in thread: rackri: "Re: Definitions"
- Reply: rackri: "Re: Definitions"
- Reply: Universe: "Re: Definitions"
- Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]
Date: Tue, 21 Oct 2003 13:04:24 -0400
"rackri" <rackri@yahoo.it> wrote in message
news:7a2f224b.0310190050.39f26b50@posting.google.com...
> Hi all,
>
> can you please help me to understand these concepts:
>
> - delegation
Class A requests Class B to perform an operation that is integral to the
key use case responsibility of Class A.
The request from Class A to Class B is not just any operation but an
operation that is essential to 'is-a' nature/character of Class A.
The reason the operation is essential to Class A is because delegation
in OO is identified with being a mechanism used *in lieu* of
*inheritance*.
Studies show that in general inheritance is more efficient regarding
space and time. However there are other pro and con contexts where many
find that delegation is preferable to inheritance.
Finally, delegation implies a "part/whole" relationship between Class A
and Class B, where Class B is perceived to be a "part" of the whole
essential role responsibility of Class A. The particular form of
"part/whole" relationship between the 2 classes may vary.
The relationship may be - "aggregate", "composition", "uses", simple
"association", or other. Context and design tradeoffs determine which
kind of "part/whole" relationship between Class A and Class B is optimal
in any given circumstance, or set of circumstances.
[This is 1 reason it would be a travesty, or is a travesty, for UML
authors to "give up" on defining, including, and distinguishing amongst
"aggregation", "composition", and "uses" as significant notational
elements of UML.]
> - forwarding
Forwarding is the passing along of data or activation signal(s) from one
class to another.
Forwarding is what Class A does when "sending", "invoking", "dispatching
to" Class B. However Forwarding is not limited to Delegation.
Forwarding may occur with Delegation or some other relationship between
the sending and receiving classes.
> - indirection
"Indirection" is when Class A invokes, dispatches to a method on Class B
by using the address of the method rather than directly by the name of
the method. "Indirection" is also what happens when Class A sends data
to Class B using the address of the data as opposed to directly
referring to the value of the data.
In all of this Class A is operating by calling methods or passing data
by "reference" versus directly "by value". C/C++?Pascal/VB pointers are
frequently used and notable a mechanisms used by one code module to make
a method call, or send data "by reference", that is by "Indirection".
> - redirection
"Redirection" is possible with "Indirection". Class A may think it is
sending data to Class B or calling a method on Class B, but Class C, or
other process inserts the address of some other module. So that the
call or send by Class A has been "Redirected", via "Indirection".
Elliott
--
*~* Theory Leads, Practice Verifies *~*
*~* Global Plans + IID (Iterative & Incremental Development) *~*
--
Substituting Refactoring For Analysis Modelling and Review
When Facing Major High Level Design Problems
Is Like Drawing a Shade When Totally Dark
- Next message: Steve: "Re: Basic books on OOA&D"
- Previous message: Dave Benjamin: "Re: OOD Refactoring RDMS Newbie!"
- In reply to: rackri: "Definitions"
- Next in thread: rackri: "Re: Definitions"
- Reply: rackri: "Re: Definitions"
- Reply: Universe: "Re: Definitions"
- Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]
Relevant Pages
|
|
