Database Reference
In-Depth Information
Commercial language implementations are based on these two generic
languages.
Two methods for creating a relational data model: transformation method, in
which you create a semantic model first and then transform it into a relational
model; traditional method, in which you come up with a set of initial tables and
then normalize the tables to produce a correct relational model.
REVIEW QUESTIONS
1. List and explain the major strengths of the relational data model.
2. “The relational data model is based on a single modeling concept.” Do you
agree? Explain.
3. What is an attribute domain? Describe with an example.
4. How is the relationship between two related tables established? Explain with
an example.
5. What are data integrity constraints? What purposes do they serve in a rela-
tional data model?
6. Describe the referential entity rule with an example. What is the consequence
of violation of the rule in a relational data model?
7. What are functional dependencies? Explain with examples.
8. Name any six of the relational algebra operations. Give examples for any two
of these operations.
9. “Relational calculus is a nonprocedural language.” Explain briefly with an
example.
10. What are the two methods for creating a relational data model? Under what
conditions would you prefer one method to the other?
EXERCISES
1. Indicate whether true or false:
A. In a relational data model, columns are identified by their names.
B. Each table or relation can contain only a specified number of rows or
tuples.
C. If the foreign key value of a row in one table is equal to the primary key
value of a row in another table, the two rows are related.
D. A null value in a foreign key attribute signifies a mandatory
relationship.
E. In a relational data model, the order of the rows is insignificant but the
columns must be in order, with the primary key as the first column.
F. The foreign key attribute in one table and the primary key attribute in the
related table must have the same column name.
G. The SELECT and PROJECT operations work on single relations.
H. The JOIN operation can operate only on union-compatible relations.
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