Page 184 - DCAP402_DCAO204_DATABASE MANAGEMENT SYSTEM_MANAGING DATABASE

Unit 10: Datalog and Recursion

10.9 Self Assessment Notes

Fill in the blanks:
1. .................................. can be a part of only one generalization hierarchy.

2. A relational query language inspired by ..................................
3. Each application of a Datalog rule can be understood in terms of ..................................
4. The .................................. semantics is thus operational and plays a role analogous to that of
relational algebra semantics for non-recursive queries.
5. A model is a collection of relation ..................................
6. .................................. disallow unsafe programs by requiring that every variable in the
head of a rule must also appear in the body.
7. .................................. is a powerful and widely used method for representing common
characteristics among entities while preserving their differences.

8. .................................. unique to a category, are assigned to the appropriate subtype.
9. A generalization hierarchy can either be overlapping or ..................................
10. In an .................................. hierarchy an entity instance can be part of multiple subtypes.

10.10 Review Questions

1. What do you mean by generalization?

2. Explain hierarchies types in generalization.
3. Describe least model semantics.

4. What do you mean by safe datalog program? Explain
5. “A model is a collection of relation instances, one instance for each relation in the program”.
Discuss

6. Describe negation and recursive queries in detail.
7. “A refining transformation is an operation which changes the frame of reference of a
process while preserving its extension, producing a process description of the same process
under a different frame of reference”. Explain

8. “A generalization hierarchy is a structured grouping of entities that share common
attributes”. Explain
9. Describe the rule of generalization hierarchy.

10. Write short note on datalog.

Answers: Self Assessment

1. Subtypes 2. Prolog
3. relational algebra 4. fixpoint
5. instances 6. Database systems

LOVELY PROFESSIONAL UNIVERSITY 177