database design techniques : (Bottom Up approach)

Concentrating on the database structures and constraints during conceptual database design

ER models are readily translated to relations.ER models, also called an ER schema, are represented by ER diagrams.

It is useful in developing a conceptual design for the database & is very simple and easy to design logical view of data.

The ......... model describes data as entities, relationships, and attributes

Without ER diagrams you can make a database structure & write production code

An ............ is a property of an entity or a relationship type.

is a set of meaningful associations among entity types

is a group of objects with the same properties, which are identified by the enterprise as having an independent existence

property or characteristic of an entity type (often corresponds to a field in a table)

–link between entities (corresponds to primary key-foreign key equivalencies in related tables)

Ellipses

Diamonds: entity sets

A definable thing—such as a person, object, concept or event—that can have data stored about it.

Think of entities as .........

can be defined solely by its own attributes.

An entity set that do not have sufficient attributes to form a primary key

An entity is considered ........ if its tables are existence dependent. That is it can not exist without relationship with another entity.

The primary key is indicated in the ER model by underlining the attribute

Primary key can have no value .

In the primary key Value should not change over time