Data integrity and Normalization Interview

What is Data integrity

What is data integrity?

Data integrity refers to the correctness and consistency of data. Integrity is usually expressed interms of certain constraints. These are the consistency rules that can be applied to database so that the correct data can be entered into database.

What is meant by entity integrity?

The entity integrity is a constraint on primary key value of a relation. It states that in a relation no primary key value can have a null value. By definition, a primary key is used to identify tuples uniquely. If one or more tuples have null value in the primary key attribute, then you cannot identify tuples uniquely.

How is entity integrity attainted?

Entity integrity Is attained achieved by specifying the primary key in the relation. No primary key value can have a null value. If no value is entered in primary key field  then DBMS display an error message. If primary key consists of composite key then entity integrity is also applied to all attributes that are part of the primary key.

Define the referential integrity?

The referential integrity is a constraint on foreign key value of a relation. It states that if a foreign key exists in a relation, then the foreign key value must match the primary key value of some tuple in its parents relation.

How is referential integrity achieved?

Referential integrity is achieved by establishing relationship between two tables. One table called parent table that contains the primary key. Other table contains the foreign key. The foreign key value must match the primary key value of some tuple in its home (parent) relation.

Differentiate between synonyms and homonyms?

When two different names are used for the same information (attribute), it is called synonym. When same name is used for two different attributes, it is called homonym.

What do you mean by mutual exclusive of data?

Tow events are said to be mutually exclusive if they cannot occur at the same time. Mutually exclusive data problem is created when the value of attributes are stored as “ture/false”. Sometime two or more such attributes cannot be true or false at the same time.

What are database anomalies?

Database anomalies or errors represent problems in relations. These problem occur due to the data redundancy in relations. These problem are also refered to as update anomalies. The update anomalies create problem when insertion, deletion and modification

What is insertion anomaly?

Suppose we want to store the information that the cost of car is Rs. 1400000, but we cannot enter this data into the relation until the complete data about the car is entered into the relation.

What is deletion anomaly?

Deletion anomaly is related to the deletion of records form the relation. It indicates that by deleting a fact about an entity, we unconsciously delete other facts aobut that entity.

What is modification anomaly?

Modification anomaly is related to the modification of records in the relation. It indicates that if we change a specific value of the attribute of a particular entity then we must update each of the rows (tuples) for the entity.

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