DB Diagram: Modality Difference between NOT NULL and check constraint

Hi,
I am using jdev 11g (11.1.1.10) I am trying to create a db diagram from two tables. I have a FK that is NOT NULL (defined on the column). When i try to display these two tables modality, it does not show up in the diagram. I noticed that there are two ways NOT null can be defined on a table (right click on the db object to edit it; a) under column definitions there is a check box for not null, b) there is a check constraint that one can add to do not null.
I am confused and was wondering whether I must I have check constraints on the database in order to display modality (optional versus mandatory). Logically speaking it does not make any sense though.

Hi Susan,
Thanks for your email. I understand that in order to show modality under
UML notation, one must define a COLUMN being NOT NULL instead of defining a check constraint.
I still do not understand how modality (optional versus mandatory) is shown in ERD notation in JDev. I tried flipping ERD/UML notations and made sure icons for tables were showing, but no MODALITY is shown in ERD notation ( an '0" icon or a "|" icon for optional and mandatory). Is it the solid line versus dotted line in the ERD diagram? I am confused because generally under Crawfoot ERD notation '0" icon or a "|" icon is shown for modality.
Modality gets picked up in jdev diagram when COLUMN not null is specified and UML notation is used
ALTER TABLE DETAILAJ MODIFY EMPID not null;
Modality does not get picked up in jdev db diagram when check constraint is specified and UML notation is used
ALTER TABLE DETAILAJ
ADD CONSTRAINT CK_NN_DETAILAJ__EMPID CHECK(EMPID IS NOT NULL) ;
Another question i have related to the matter mentioned above is as follows. Since I want to see modality in db diagram, it follows that I must define a column as not null instead of a check constraint. I must also use NO VALIDATE on NOT NULL column because i have prior data that does not meet the new restriction. I noticed that if i use the following syntax to define a NOT NULL column, two things happen.
a) A constraint is defined as not null automatically and a system generated name is given to the constraint.
b) DB diagram in Jdev does not show the modality.
My question is whether there is a way to see modality in this case.
alter table DETAILAJ
MODIFY EMPID NOT NULL ENABLE NOVALIDATE ;
Edited by: user11219846 on Nov 19, 2009 11:07 AM

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I am really get confused with it, and
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>
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B
C
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D
E
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G
H
a1
b1
c1
1
1
e1
f1
g1
h1
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c2
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3
e2
f2
g2
h2
a3
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c3
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4
e3
f3
g3
h3
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c4
3
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Note
In some cases, '*' may be specified in the SELECT clause, and an internal table or work area is entered into the INTO clause (instead of a list of fields). If so, the fields are written to the target area from left to right in the order in which the tables appear in the FROM clause, according to the structure of each table work area. There can then be gaps between table work areas if you use an Alignment Request. For this reason, you should define the target work area with reference to the types of the database tables, not simply by counting the total number of fields. For an example, see below:
Variant 3
... FROM tabref1 LEFT [OUTER] JOIN tabref2 ON cond
Effect
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A
B
C
D
D
E
F
G
H
a1
b1
c1
1
1
e1
f1
g1
h1
a2
b2
c2
1
3
e2
f2
g2
h2
a3
b3
c3
2
4
e3
f3
g3
h3
a4
b4
c4
3
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