Class 12 Computer Science Chapter 4 Notes

• Explain Data Integrity: Database integrity refers to the correctness and consistency of data. It is another form of database protection. While it is related to security and precision, it has some broader implications as well. Security involves protecting the data from unauthorized operations, while integrity is concerned with the quality of data itself. Integrity is usually expressed in terms of certain constraints which are the consistency rules that the database is not permitted to violate. Following two are the most important constraints in relational databases
• Explain Normalization:  [It is the process of converting complex data structures into simple and stable data structures. It is based on the analysis of functional dependence]. [Normalization is a technique for reviewing the entity / attribute lists to ensure that attributes are stored “where they belong to”. It is the basis for a relational data base system]. In practice, it is simply an applied common sense. More formally stated, [it is the process of analyzing the dependencies of attributes within entities. Attributes for each entity are checked consecutively against three sets of rules, making adjustments when necessary to put the entity in First, Second and Third normal form]. “A functional dependency is a particular relationship between two attributes. For any relation R, attribute B is functionally dependent on attribute A if, for every valid instance of A, that value of A uniquely determines the value of B” The functional dependence of B on A is represented by an arrow. 
• Define Normalization and Normal Form: [It is the process of converting complex data structures into simple and stable data structures. It is based on the analysis of functional dependence]. [Normalization is a technique for reviewing the entity / attribute lists to ensure that attributes are stored “where they belong to”. It is the basis for a relational data base system]. Normal Form : A Normal Form is a state of a relation that can be determined by applying simple rules, regarding dependencies (or relationship between attributes), to that relation.
• Explain First Normal Form (1 NF).
• Explain Second Normal Form (2 NF): Second Normal Form (2 NF) : [A relation is in second normal form NF (2 NF) if it is in 1 NF and every non-key attribute is fully functionally dependent on the primary key]. Second Definition : “To be in 2 NF, every non-key attribute must depend on the key and all parts of the key”. Necessary & Sufficient Conditions : A table (relation) will be in 2NF if any of the following conditions apply : The primary key consists of only one attribute. No non-key attributes exist in the relation. Every non-key attribute is functionally dependant on the full set of primary key attributes. 
• Explain Third Normal Form (3 NF) and Transitive Dependency: Third Normal Form (3 NF) : [A relation is in third normal form (3 NF) if it is in 2 NF and no transitive dependencies exist]. Transitive Dependency : [It is a functional dependency in a relation between two or more non-key attributes]. Third Normal Form (3 NF) – Second Definition : A more precise definition for 3 NF is : “A non-key attribute must not depend on any other non-key attribute” or “if a non- key attribute’s value can be obtained simply by knowing the value of another non-key attribute, the relation is not in 3 NF. The Anomalies, Insertion Anomaly, Deletion Anomaly and Modification Anomaly must be related with example data. These anomalies arise as a result of the transitive dependency. This problem (the transitive dependency) can be removed by de-composing the a relation into two relations.