Section 7

Question 1

…………..: A restriction that applies to data, which is often dictated by the business rules.

Answer 1

Constraint

Question 2

Mutually exclusive relationships sometimes exist between entities and are also known as ………. ………. ……….

Answer 2

Exclusive OR Relationships

Question 3

……….. ……….. ………..: A relationship between one entity and two (or more) other entities where only one of the relationships can exist at a time.

Answer 3

Mutually exclusive relationship

Question 4

In ERDs, we model Exclusive OR Relationship relationship with an ……….

Answer 4

Arc

Question 5

………. ……….: A logical operator that returns a true value if one, but not both, of its operands is true.

Answer 5

Exclusive OR

Question 6

Answer 6

Question 7

A …………. is drawn on the arc for every relationship that is part of the arc

Answer 7

circle

Question 8

If a relationship crosses an arc but it is not part of the Exclusive OR Relationship, the circle is ………….

Where possible, for clarity and ease of reading the diagram, this should be avoided by drawing relationships that are not part of the arc outside the arc.

Answer 8

omitted

Question 9

1. An arc always belongs to ……… entity
2. Arcs can include more than two …………..
3. Not all relationships of an …………… need to be included in an arc
4. An entity may have several …………..
5. An arc should always consist of relationships of the same ………………

Answer 9

1. one
2. relationships
3. entity
4. arcs
5. optionality

Question 10

1. All relationships in an arc must be ………….. or all must be …………..
2. Relationships in an arc may be of different ……………, although this is rare

Answer 10

1. mandatory / optional
2. cardinality

Question 11

Arcs and Super/subtypes both model ………. …………

Answer 11

mutual exclusiveness

Question 12

Certain situations are best modeled as an arc, and others as ………………….

Answer 12

supertype and subtypes

Question 13

1. It can be confusing as to when to use an arc vs. a supertype/subtype.
2. Super/subtypes are Mutually exclusive – in other words, each instance of a supertype is an instance of only one possible subtype.
3. Arcs represent a Mutually exclusive relationship.

Answer 13

R 2

Question 14

Use supertypes/subtypes when you want to represent ……………. or ………… of things.

Answer 14

classifications / types

Question 15

Arcs model an Exclusive OR constraint. T or F?

Answer 15

True

Question 16

Answer 16

Question 17

Read 7-2

Answer 17

Read 7-2

Question 18

Another thing to consider when modeling these types of relationships is how often the structure changes. If it changes often, then a …………. relationship is easier to maintain. If it is fairly fixed, then you may consider the more explicit ………….

Answer 18

recursive / hierarchy

Question 19

The ERD convention to show a recursive relationship is drawn as a loop, also known as a “…………….”

Answer 19

pig’s ear