Lecture 4

Question 1

What is a Data Model ??

Answer 1

• A set of concepts to describe the structure of a database
• the operations for manipulating the structure of a database
• the constraints that the database should obey.

Question 2

What are the 2 Categories/types of Data Models ?

Answer 2

1) Conceptual (high-level, semantic) data models

2) Physical (low-level, internal) data models

3) Implementation (representational) data models

Question 3

what does the conceptual data type model do?

Answer 3

▪ Provide concepts that are close to the way many users perceive data.

Question 4

what does the physical data type model do ?

Answer 4

▪ Provide concepts that describe details of how data is stored in the computer.

Question 5

what does the Implementation (representational) data models do ?

Answer 5

▪ Provide concepts that fall between the conceptual and the physical data models
▪ used by many commercial DBMS implementations (e.g. relational data models used in many
commercial systems).

Question 6

• Informally, a ……….. looks like a table of values.
• The data elements in each row represent certain facts that correspond to a real-world ……. or ……..
• In the formal model, rows are called ………
• In the formal model, the column header is called an ……….

Answer 6

• relation
  -entity or relationship
• rows are called tuples
• attribute)

Question 7

The …………of a Relation:
- is Denoted by R(A1, A2, …..An)
- R is the name of the relation
- The attributes of the relation are A1, A2, …, An

Answer 7

• Schema (or description)

Question 8

Each ………… has a domain or a set of valid values.
For example, the domain of Cust-id is 6 digit numbers.

Answer 8

attribute

Question 9

A ………..is an ordered set of values (enclosed in angled
brackets ‘< … >’)

Answer 9

tuple