EPFL - Databases - Quiz 1b
ER Model
1) Which step of database design is related with the ER model:
Physical Database Design
Security Design
Requirements Analysis
Schema Refinement
2) An entity is:
a real-world object
the set of all values of one concept
a property of a concept
the set of all values of a property
3) The minimum degree of a relationship is:
2
3
|
E
|, {
E
= E(i),entity}
infinite
4) Let's assume the entity types S and T. A relationship from S to T which an entity from T can be related to two or more entities from S is:
1:1
1:N
N:1
N:M
5) Aggregation conceptually transforms ... such that the resulting construct can be related to other entity sets.
an entity set into a relationship set
a relationship set into an entity set
an entity into a relationship
a relationship into an entity
Relational Model
6) A Relational Model is a:
Data Model
Hierarhical Model
Database Model
Object-oriented Model
7) A relation schema has 3 fields d1, d2, d3 of types D1, D2, D3, respectivelly. The types are sets of size m, n, p respectivelly, and (d1, d3) and (d2) are candidate keys for the relation. What is the maximum number of tuples in a relation instance of this relation schema?
min(m * p, n)
max(m * p, n)
n * (m + p)
(m * p)/n
8) A relation schema has 3 fields d1, d2, d3, and the only candidate key is d2. How many superkeys exist in this relation schema?
2
3
4
5
9) A foreign key is:
A field in a table, and this field's values are also contained elsewhere in another table.
A field in a table, and this field's values are among the values of a key field in another table, or NULL.
A field in a table that has the same name as a key field in another table.
A key that consists of more than one field.
10) The ER to Relational function dictates that a weak entity must reference the primary key of the owner entity. To ensure the weak entity does not exist without its owner entity, the foreign key declaration must contain the specification:
ON DELETE CASCADE
ON DELETE NO ACTION
ON DELETE SET DEFAULT
ON DELETE SET NULL
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