midterm_practice

Question 1

Select the options which are True about weak entities.
1. Weak entities can’t have subclasses.
2. Weak entities can be identified uniquely by considering the primary key of another owner entity, and its own partial key
3. The relationship type that relates a weak entity to its owner is called the partial relationship.
4. in relation to an ER diagram, a weak entity is represented with double lines.

Answer 1

2&4

reason:
1. weak entities can have subclasses(not common, but possible)

3. A weak entity type always has a total participation constraint with respect to its idenfitying relationship

Question 2

A delivery system for an ice cream factory records every box produced and shipped to
different destinations. Each box is identified by the type of ice cream stored and label number. Each box has the type of box, volume of ice cream, time, and date packaged recorded. The date consists of the day, month and year. Every box type has known dimensions. Before transportation, all boxes must be approved by a supervisor with a name, contact details, date employed and unique identification number. Only one supervisor is required to oversee and send off boxes. The unique transport ticket code, expected end location and arrival date is recorded.

Q. Choose False option(s)

A) The cardinality of the relationship between supervisors to boxes is 1-N.
B) The boxes are in total participation to its relationship with supervisors.
C) The type of box can be derived by its measured dimensions.
D) There is a composite key attribute for one of the entities.
E) The label number does not have to be unique for every box.

Answer 2

E

Question 3

explain “Semantic Integrity Constraint”

Answer 3

Constraints that cannot be directly expressed in the schemas of the data model referred to as semantic constraints or business rules.

Question 4

explain “key constraint”

Answer 4

it happens when you try to insert that is not unique(already exist in the database)

Question 4

explain “Referential integrity constraint”

Answer 4

it requires that a FK must match a primary key in another table or be null.

Question 5

explain “domain constraint”

Answer 5

it specifies that within a database, each attribute must de declared upon a defined domain(same data types).