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Slide 14.11: Transformation rule 4. N-1 relationships Slide 14.13: Cardinality of attributes Home         Print version

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Transformation Rules (Cont.)

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Transformation Rule 5. 1-1 Relationships, Optional Participation
Given two entities E and F take part in a 1-1 relationship:

• Create tables S and T to represent E and F, respectively.


• Adjoin to the table T a set of columns of the primary key for S.

Below shows the one-to-one relationship own, where a PC can be owned by at most one professor or no one, and a professor can own at most one PC or none. The relationship own is not mapped to any table.

The table PC now includes a column from the primary identifier of the entity professor.
PC pc_num pc_brand fac_id 309 ACER 123 405 Dell 145 213 IBM 167 ... ... ...		professor fac_id fac_name office 123 Smith MC78 145 Jones MC27 213 Thomas LI12 ... ... ...

Transformation Rule 6. 1-1 Relationships, Mandatory Participation on Both Sides

• Combine the tables for the two entities into one.

Below shows the one-to-one relationship is_in, where an office is owned by one and only one professor, and a professor can own one and only one office.

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professor fac_id fac_name office 123 Smith MC78 145 Jones MC27 213 Thomas LI12 ... ... ...

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