database design process
two main activities:
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database design
-
applications design
database design : to design the conceptual schema for a database app
conceptual design: view of the collected data is seperated
logical design: logical model/rows in the database is created
Er model [entity representation model]
pictorial rep of database
high lvl conceptual data model
used for conceptual data design of database
easy to understand for non technical users
ER model concepts
entity/entity type: any real world object are entuty
eg: EMPLOYEE, DEPARMENT, PROJECT, COLLAGE, etc(ALWAYS IN CAPITAL)(table name in sql)
entity type: property of the entity is the entity attributes
entity set: set of entities which is stores in hte table is the entity set
entity type/attribute
domain: allowed or permitted value in the attribute (char[20],int less than 25, )
ENTITY is repr by rectangle
Attributes is repr by oval
Type of Attributes
simple attribute
attributes which cannot be further divided
eg:city,age,state,et
composite attr
it can be composed of several components
eg: address(house,street,city,state,zip,country), fullname(first,middle,last)
multi-valued attr
an entity may have multiple valiues for that attr.
repr by double oval
complex attr
combi of composite and multi-valued attr
eg: {degree(college,year,degree,field)}
key attr
attr which is unique to an entiyt is called key attr.
repr as underline in ER diagram
Stored vs derived attr
attr which can be calculated from another attr
eg:age form DOB dateofbirth
repr as dotted line