Technical Interview Questions and Answers :: iGate

1. Reduces Data Redundancy

2. Maintains Data Consistent

3.Query to access data

4. Security

5. Easier access by tables

1. Redundant Data

2. Inconsistency

3. Not easy to access data.

4. No security

5. Concurrent access is not allowed.

Physical Level - This is the lowest level of data abstraction which describes which describes how the data is to be stored in the database.

Logical level - The level describes the data in the database as well as relations between these database.

View Level- This is the highest level of data abstraction , only some part of actual database is viewed to the user.

There are two Integrity rules.
> Entity Integrity: States that “Primary key cannot have NULL value”
> Referential Integrity: States that “Foreign Key can be either a NULL value or should be Primary Key value of other relation.

System R was designed and developed over a period of 1974-79 at IBM San Jose Research Center. It is a prototype and its purpose was to demonstrate that it is possible to build a Relational System that can be used in a real life environment to solve real life problems, with the performance at least comparable to that of the existing system.
Its two subsystems are
> Research Storage
> System Relational Data System.

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.

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

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