Prof. Gordon Everest
TA: Guy Gaskin
Time on Hw #1: 3 hours
Assume that the diagram reflects good database design practice, which means it is in third normal form. Attribute A does not allow null values, while attribute B allows null value. There exists another entity identified by Y which has a relationship with the current entity identified by X. There is a third entity identified by C. C is the third non-key attribute in the entity identified by X.
1. There exist domains of values called X, A, B, Y, and C etc.
2. These domains of values (mentioned in 1) exist without dependency on the entity instance or each other. Strictly speaking, these domain of values are matters of fact.
3. This diagram defines a table which contains information about a set of entities (in rows) describe by values for attributes named A, B, etc. (in columns.)
4. Each entity instance is uniquely identified by the value of an attribute X, called identifier.
5. Each entity instance has one and only one attribute X.
6. Each entity identified by X has one and only one value for attribute A.
7. Each entity identified by X has at most one value for attribute B.
8. Each existing value of attribute A or B on record describes at least one entity.
9. Attribute A and B has zero relationship with each other. (It does not matter whether they are the same values because the system does not recognize the relationship between the two in a fully normalized database.)