Week 2 - Conceptual Modeling

Question 1

What are the 5 steps of Database design? Briefly describe them

Answer 1

1. Requirement analysis - specify what is needed to be modeled in a real world domain
2. Conceptual design - complete technology independent picture of the db
3. Logical design - refine a conceptual model to a schema using the data model of a dbms
4. Physical design - define the schema using DDL of the dbms
5. Database creation - load data into the db

Question 2

Define the following terms and draw examples,
1. Entity
2. Attributes
3. Relationship
4. Degree
5. Role

Answer 2

1. A real world object distinguishable from other objects
2. Each entity is described by a set of attributes.
3. An association between two or more entities.
4. Number of entity types involved in a relationship
5. Part played by entities of a unary relationship

Question 3

What are the 3 ways attributes can be classified as? Give examples.

Answer 3

1. simple vs composite
2. single value vs multi-value
3. stored vs derived

Question 4

What is a domain of an attribute?

Answer 4

The set of values an attribute may take

Question 5

• What are key attributes?
• What is key constraint?

Answer 5

• A set of attributes for an entity type that are unique for each entity of that type.
• Every entity type must have at least one key attribute.

Question 6

• What is cardinality ratio?
• List the three types of cardinality restraints. Show examples

Answer 6

• Number of relationships an entity can participate in.
  1. 1-to-1
  2. 1-to-N
  3. N-to-M

Question 7

What is a weak entity? List 2 properties.

Answer 7

An entity type without its own key
1. has a partial key
2. must participate in an identifying relationship with a strong entity type.

Question 8

What are the concepts included in ERR model?

Answer 8

1. Subclass and superclass
2. Specialization and generalization
3. Category or union type
4. Attribute and relationship inheritance

Question 9

Provide an example of Subclass/superclass concept

Answer 9

Give.

Question 10

Give examples for specialization and generalization

Answer 10

Give.

Question 11

What are disjointness and completeness constraints?

Answer 11

These two are independent properties.
Disjointness: Subclass of a specialization is disjoint. (give example)
Completeness: Maybe total or partial. (give example)