Technical Interview Questions and Answers :: DBMS

Physical level

A view may be thought of as a virtual table, that is, a table that does not really exist in its own right but is instead derived from one or more underlying base table. In other words, there is no stored file that directly represents the view instead a definition of the view is stored in data dictionary.
Growth and restructuring of base tables are not reflected in views. Thus the view can insulate users from the effects of restructuring and growth in the database. Hence accounts for logical data independence.

A collection of conceptual tools for describing data, data relationships data semantics and constraints.

This data model is based on the real world that consists of basic objects called entities and of a relationship among these objects. Entities are described in a database by a set of attributes.

This model is based on a collection of objects. An object contains values stored in instance variables within the object. An object also contains bodies of code that operate on the object. These bodies of code are called methods. Objects that contain same types of values and the same methods are grouped together into classes.

It is a 'thing' in the real world with an independent existence.

It is a collection (set) of entities that have same attributes.

It is a collection of all entities of a particular entity type in the database.

The collections of entities of a particular entity type are grouped together into an entity set.

An entity set may not have sufficient attributes to form a primary key, and its primary key compromises of its partial key and the primary key of its parent entity, then it is said to be Weak Entity set.