Information Technology Reference
In-Depth Information
Step 1—Reverse engineering from relational model to conceptual EER model
(Navathe and Awong
1988
).
The translation process can be described as follows:
Substep 1—Define each relation, key, and field.
The relations are preprocessed by making any necessary candidate key substitu-
tions as follows:
• Primaryrelation.Theserelationsdescribeentities.
• Primaryrelation—Type1(PR
1
). This is a relation whose primary key does not
contain a key of another relation.
• Primaryrelation—Type2(PR
2
). This is a relation whose primary key does con-
tain a key of another relation.
• Secondaryrelation.Thisisarelationwhoseprimarykeyisfullyorpartially
formed by concatenation of primary keys of other relations.
• Secondaryrelation—Type1(SR
1
). If the key of the secondary relation is formed
fully by concatenation of primary keys of primary relations, it is of Type 1 or
SR
1
.
• Secondaryrelation—Type2(SR
2
). Secondary relations that are not of Type 1.
• Keyattribute—Primary(KAP).Thisisanattributeintheprimarykeyofasec-
ondary relation that is also a key of some primary relation.
• Keyattribute—General(KAG).Thesearealltheotherprimarykeyattributesin
a secondary relation that are not of the KAP type.
• Foreignkeyattribute(FKA).Thisisanon-primarykeyattributeofaprimary
relation that is a foreign key.
• Non-keyattribute(NKA).Therestofthenon-primary-keyattributes.
For example, the following relations are for an university enrollment system:
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The following relations and attributes classification table is derived:
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