Hello,
For 3. below in my original email at bottom, is this also true for
aggregation relationships?
For example below, there are 3 classes with their key fields:
Class A: Industry_Code
Class B: Industry_Code, Cycle_Code
Class C: Industry_Code, Cycle_Code, Version_ID
1 Class A maps to many Class B; 1 Class B maps to many Class C. Their
relationships are aggregate relationships (or identifying relationships).
And, in object model, Class A will contain Industry_Code (key field); Class
B will contain Cycle_Code (key field) without Industry_Code; Class C will
contain Version_ID without Industry_Code and Cycle_Code?
Thanks again.
Yue-Hwa
-----Original Message-----
From: Gornik, Davor [mailto:[EMAIL PROTECTED]]
Sent: Wednesday, May 29, 2002 5:43 PM
To: Chang_Y; '[EMAIL PROTECTED]'
Subject: RE: (ROSE) rational rose data modeler questions
Yue-Hwa,
You are right with all three statements. Let me explore it a little bit more
below...
Regards,
Davor Gornik
-----Original Message-----
From: Chang_Y [mailto:[EMAIL PROTECTED]]
Sent: Wednesday, May 29, 2002 2:31 PM
To: '[EMAIL PROTECTED]'
Cc: Chang_Y
Subject: (ROSE) rational rose data modeler questions
I have been using rational rose data modeler to create "logical ERD" in
object model.
Questions:
1. Can the object model display the "key" (i.e. Part of Object Identity)
field?
(I know it can be displayed in data model.)
[Gornik, Davor] You are right: we can not display it on the diagram. Often I
use a stereotype to display it - for example <<Identifier>>
2. I have been using Association for non-identifying relationship and
Aggregation by Value for identifying relationship. Is this correct? Does
it cover all the relationships in data model?
[Gornik, Davor] This is one of the possibilities. The logical model in UML
is richer and contains not only aggregation and association. For example you
could use subtyping (inheritance) instead of aggregation. All of these
really depend on the kind of relationships between objects. The logical
model should use "natural" relationships, the physical model is constrained
by the database.
3. For Association relationship, I should not add "foreign key" in the
related Class because when transforming to data model, the foreign key will
be added automatically.
e.g.
INDUSTRY Class
attributes: Industry_Code (key), Industry_Title
ITEM Class
attributes: Item_Code (key), Item_Price
And one INDUSTRY maps to many ITEM; Industry_Code will be added to ITEM
class as foreign key in data model.
[Gornik, Davor] Yes, you are right again. The association itself contains
the key definition. The physical implementation of the database will define
what constraint to use and depends on the physical implementation and not
only on the logical relationship.
Also, I'd appreciate it if you have other valuable experiences about the
tool to share.
Thanks.
Yue-Hwa
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