12th Class Computer Science Chapter 4 Short Questions with Answers Online Preparation

Question # 1

Ans 1: A homonym is created when same name is used for two attributes. Consider the following example :Customer SupplierCompany_Name Company_NameWe Should use Supplier _Name instead of Company _Name in Supplier

Question # 2

Ans 1: Normalization:Normalization is the process of converting complex data structures into simple and stable data structures. It is based on the analysis of functional dependence . In other words, Normalization is a technique for reviewing the entity/ attributes lists to that attributes are stored " where they belongs ".it is base for a relational data base system .There are three Forms of Normalization:a) First Normal Formb) Second Normal Formc) Third Normal Form

Question # 3

Ans 1: A synonyms is created when two different names are used from the same information (Attributes) . If an attributes resides in more than one entity , make sure that all entities use the same attribute name.

Question # 4

Ans 1: An Insert Anomaly occurs when certain attributes cannot be inserted into the database without the presence of other attributes. For Example this is the converse of delete anomaly.we can't add a new course unless we have at least one student enrolled on the course.

Question # 5

Ans 1: Mutually exclusive data exist when attributes occur whose values can be expressed as "Yes/no" indicators , cannot all be true for any single entity.

Question # 6

Ans 1: A relation is in third normal form (3 NF) if it is in 2 NF and no transitive dependencies exist.A more precise definition for 3 NF is : "A non-key attribute must not depend on any other non-key attributes " or if a non-key attributes value can be obtained simply by Knowing the value of another non-key attribute, the relation is not in 3 NF.

Question # 7

Ans 1: A partial functional dependency exist when one or more non- key attributes (Such as NAME) are functionally dependent on part (but not all) of the primary key

Question # 8

Ans 1: Database Anomalies: Anomalies are problems that can occur in poorly planned, un-normalized database where all the data is stored in one table (a flat -file database)Types of Anomalies:a) Insertion Anomalyb) Deletion Anomalyc) Modification Anomaly

Question # 9

Ans 1: A relation R is in First Normal Form if and only if all underlying domains contain atomic values only.The Pre-requisite is that, A relation has a always a primary key associated with it. Thus, we can define it as follow:1) All entities must have a key,composed of a combination of one or more attributes which uniquely one occurrence of the entity.2) For any single occurrence of an entity,each attribute must have one and only one value or "An attributes must have no REPEATING GROUPS".

Question # 10