CONCEPTUAL MODELLING

-USING ERD (entity relationship diagram)

-FOCUS ON CHEN NOTATION

ERD

-pictorial representation of database structure .

-different shapes of items

-entities

-attributes

-relationships

-cardinality

-connectivity

ENTITIES

-person, object, place

-entity set

-correspond to table

-represented by a rectangle

-singular noun

-CAPS Lock

e.g= EMPLOYEE, STUDENT, WAREHOUSE, COURSE

RELATIONSHIPS

-association between the instances of one or more entity types

-use verbs

-connectors

-in diamond shape

ATTRIBUTES

-named property or characteristic of an entity

-represents in oval

-unique

-contain foreign key

-contain composite and single attributes

CONNECTIVITY

-Relationships can be classified as either

•one – to – one

•one – to – many

•many – to –many

CARDINALITY [endif]

-minimum and maximum number of instances of Entity B that can (or must be) associated with each instance of entity A.