The candidate key that is selected to identify tuples uniquely within the relation.

Candidate key: when a key consists of more than one attribute

Super key : An attribute, or set of attributes, that uniquely identifies a tuple within
a relation.

A super key such that no proper subset is a super key within the relation.

in each tuple of R, the values of K uniquely identify that tuple

Additional rules specified by the users or database administrators of a database that define or constrain some aspect of the enterprise.

View : The dynamic result of one or more relational operations operating on the base relations to produce another relation

Represents a value for an attribute that is currently unknown or is not applicable for this tuple.

Null Can create problems when functions such as COUNT, AVERAGE and SUM are used

Null can represent

The database designers interview prospective database users to understand and document their data requirements.

requirements should not be specified in as detailed and complete a form.

In parallel with specifying the data requirements, it is useful to specify theknown functional requirements of the application

we create a conceptual schema for the database, using a low-level conceptual data model.

............ concepts are used for conceptual schema design

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.