Train the Trainer develops seminars and workshops for corporate training manager

Question

Train the Trainer develops seminars and workshops for corporate training managers, who in turn train their employees. Your job at Train the Trainer is to put together the actual training materials. Right now, you are up against a deadline. The new object modeling seminar has a chapter on cardinality, and the client wants you to come up with at least three more examples for each of the four cardinality categories listed in Figure 6-29 on page 239. The four categories are zero or many , zero or one , one and only one , and one or many . Even though you are under pressure, you are determined to use examples that are realistic and familiar to the students. What examples will you submit?

Explanation / Answer

In the implementation of a structure query language (SQL), the term data cardinality is used to mean theuniqueness of the data values which are contained in a particularcolumn,known as attribute, of a database table.

There are actually three types of data cardinality each dealing with columnar value sets. These types are high-cardinality,normal-cardinality, and low-cardinality.

1. High data cardinality

2. Normal data cardinality

3. Low data cardinality

The four categories are...

1.Zero or many : The possession cardinality is a 0:M relation (zero to many) relationship on both sides.

2 .Zero or one :   The characteristic cardinality is a 0:M relationship which is mandatory on both sides.

3 .One and One : The physical segment cardinality is 1:1 relationship and it is demonstrated that both sides of the relationship are mandatory.

4 .One or many : The paradox cardinality is 1:M relationship whichis mandatory to one side. An example would be a person table and citizenship table relationship.

For example, consider a database designed to keep track of hospital records. Such a database could have many tables like:

* a doctor table with information about physicions;

* a patient table for medical subjects undergoing treatment;

* and a department table with an entry for each division of hospital.

* There is a one-to many relationship between the department table and the doctor table because each doctor may work for only one department, but one department could have many doctors.

A "one-to-one" relationship is mostly use to split a table inorder to provide information concisely and make it more understandable. in the hospital example, such a relationship could be used to keep apart doctors own uniqueprofessional information from adminitrative details.

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