Page 42 - DCAP402_DCAO204_DATABASE MANAGEMENT SYSTEM_MANAGING DATABASE

Unit 2: Database Relational Model

2.5 Self Assessment Notes

Fill in the blanks:
1. ........................................first formulated and proposed in 1969 by Edgar Codd.

2. Consistency is achieved by including declared constraints in the database design, which is
usually referred to as the ...................................
3. A ................................... is a set of attributes.

4. A ................................. is an accepted visual representation of a relation.
5. ................................... is the term used in the theory for what is commonly referred to as a
column.

6. ............................. is a special case “join” operator which considers the NULL values.
7. .............................. is a collection of facts, which is unorganized but can be made organized
into useful information.

8. A recent development is the Object-Relation type-Object model, which is based on the
assumption that any fact can be expressed in the form of one or more .....................
9. A relation universe U over a header H is a non-empty set of relations with .......................

10. ............................... operator can be applied to only those relations that are union compat-ible.
2.6 Review Questions

1. Here we consider three tables for solving queries:

Instance S of Sailors
1

sid sname rating age
22 Dustbin 7 45.0
31 Lubber 8 55.5
58 Rusty 10 35.0

Instance S of Sailors
2
sid sname rating age
28 yuppy 9 35.0
31 Lubber 8 55.5
44 guppy 5 35.0
58 Rusty 10 35.0

Instance R of Reserves
1
sid bid day
22 101 10/10/96
58 103 11/12/96

(a) Find the names of sailors who have reserved a red or a green boat.

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