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Database Courses ? 2 (Entity ? Relationship Model )

25 Aralık 2010 1.972 views Yorum Yok

ENTITY ? RELATIONSHIP MODEL (E-R Diagram)

Entity ? Relationship model is a Database design tool for creating a diagram.

( ?entity? means record, object )

? Binary Relationship Set

? Ternary Relationship Set

There are kinds of attributes. Some of them is like that:

? Single valued attribute: at most one value

For example; firstname, lastname..

?Multi-valued attribute: 0 or more similar values. We don?t put them to the E-R diagram, but we can draw another table for it.(with primary key of the table which it belongs to)

Such as phone number, e-mail, address

?Derived attribute: It is derived from another attribute

For example, age is a derived attribute. It can not be stored. It changes and it is derived from birthdate. We don?t put them to the E-R diagram.

See you soon..

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