3.2.2 Database Modelling

Question 1

Conceptual ER

Answer 1

Investigates data needs of the organisation- what data do they need to store?

how are the data elements to be grouped- what will the entities be?

includes the entities AND the relationship between them.

Question 2

Logical

Answer 2

includes entities and their relationships

identifies all attributes, plus primary and foreign keys

normalisation occurs at this stage

Question 3

Steps for making logical data model

Answer 3

specify primary keys for all entities

find relationships between different entities

find all attributes for each entity

resolve many to many relationships

normalisation

Question 4

Differences between conceptual and logical

Answer 4

no primary key is present

all attributes are specified within an entity

relationships between entities are specifies using primary and foreign keys. in a conceptual data model, the relationships simply stated, not specified, so we know that two entities are related, but we do not specify what attributes are used for this relationship.

Question 5

Physical

Answer 5

uses the logical model as a basis

converts all entities and attributes into tables with columns

specifies the data type for each attribute

the physical model produced could be different for different database packages

Question 6

Producing ER diagram

Answer 6

look at notes