Data Base week3_3

Open source :

production that promote access to the end product's source materials—typically, their source code.

Pasted from <http://en.wikipedia.org/wiki/Open_source>

 
 

Primary Key

a unique key can uniquely identify each row in a table, and is closely related to the Superkey concept. A unique key comprises a single column or a set of columns. No two distinct rows in a table can have the same value (or combination of values) in those columns if NULL values are not used. Depending on its design, a table may have arbitrarily many unique keys but at most one primary key.

 
 

Pasted from <http://en.wikipedia.org/wiki/Primary_key>

 
 

Candidate Key

a candidate key of a relation is a minimal superkey for that relation; that is, a set of attributes such that

• the relation does not have two distinct tuples with the same values for these attributes
  
• there is no proper subset of these attributes for which (1) holds.
  

Pasted from <http://en.wikipedia.org/wiki/Primary_Key>

 
 

 
 

Crow Foot : using to indicate relationship between entities.

--<

 
 

OK	One to Many
NO	Many to One
NO	Many to Many

 
 

Home Work Exercise Sheet Week2