In a conceptual database schema, there is a superclass entity S. S has an attrib
ID: 3859817 • Letter: I
Question
In a conceptual database schema, there is a superclass entity S. S has an attribute-defined cluster of total and overlapping subclasses based on the attribute A.
There are four subclasses in this cluster. Subclass U1 entity instances should have attribute value of A as "s", subclass U2 entity instances should have attribute value of A as "m", subclass U3 entity instances should have attribute value of A as "t" and subclass U4 entity instances should have attribute value of A as "p". These are all the legal values of A. What should be the cardinality ratio of A in S?
(a) (1:1)
(b) (1:4)
(c) (0:1)
(d) (4:1)
(e) (4:4)
(a) (1:1)
(b) (1:4)
(c) (0:1)
(d) (4:1)
(e) (4:4)
Explanation / Answer
Option B
The Cardinality of a variable is the ratio of the number of rows of the frequency data set divided by the number of rows of the data set. It is a Pure Number, because it has no units.
Characteristics
1.The range is (0,...,1]; cannot be zero and can be one.
Explanation: There is at least one value for a variable:character = ' ' and numeric = .; therefore the range is 1/nobs : nobs/nobs.
If the Cardinality Ratio is one then the variable is unique and probably a Primary Key or Row Identifier.
2.The distribution of values for variables in a data has two groups: each near the extreme values of near zero and near one.
Values in the left group near zero are usually Foreign Keys;you expect a Dimension (LookUp) Table with the variable name