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.

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)