Normalization is the process of organizing the data in a database. It helps in removing the duplicate values in the database. Normalization divides the large table into smaller tables and links them using relationships.The normal form is used to reduce redundancy from the database table. Normalization is the name given to the process of simplifying the relationship among data elements in a record.In simple words we can say, Normalization is the process of organizing data to minimize.Redundancy/duplication/repetition.Insertion, deletion, updating anomalies.Normal formsThere are six Normal forms which are as follows −First Normal Form (1NF)Second Normal Form (2NF)Third Normal Form (3NF)Boyce-Codd Normal ... Read More

A trigger is a procedure which is automatically invoked by the DBMS in response to changes to the database, and is specified by the database administrator (DBA). A database with a set of associated triggers is generally called an active database.Parts of triggerA triggers description contains three parts, which are as follows −Event − An event is a change to the database which activates the trigger.Condition − A query that is run when the trigger is activated is called as a condition.Action −A procedure which is executed when the trigger is activated and its condition is true.Use of triggerTriggers may ... Read More

Let’s see the procedure to access database users in DBMS step by step.Step 1 − The request from the user is passed to the DBMS user interface, where oracle engine locates the files for the given relation.The relation is nothing but − table schemaLinking between the recordsStep 2 − The file manager will generate the particular file for the given table and process this request to the disk manager.Step 3 − The disk manager will give the offset address for the given table where the records are stored.Step 4 − The displacement of a particular block is done from hard ... Read More

In the 2NF, relation must be in 1NF. In the second normal form, all the non-key attributes are fully functional dependent on the primary key. Or a relation is in 2NF, when it is in 1NF and there is no partial dependency.ExampleConsider a relation R (rollno, name, subjectcode, subjectname, duration)RollnoNameSubjectcodeSubjectnameDuration1HariS1C60 days1HariS2Java90 days2PinkyS1C60 days2PinkyS2Java90 days3RakhiS3Database45 daysF: {rollno -> name, subjectcode -> (subjectname, duration).{rollno, subjectcode}+ = {rollno, name, subjectcode, subjectname, duration}=> {rollno, subjectcode } is candidate key.The above table is in 1NF because no multivalued attributes are present. But it is not in 2NF because the following two partial dependencies are present.Rollno->name ... Read More

The three-schema architecture divides the database into three-level used to create a separation between the physical database and the user application. In simple terms, this architecture hides the details of physical storage from the user.The database administrator (DBA) responsible is to change the structure of database storage without affecting the user’s view. It deals with the data, the relationship between them and the different access methods implemented on the database. The logical design of a database is called a schema.This architecture contains three layers of database management system (DBMS) −External levelConceptual levelInternal levelThe three layers of the DBMS are pictorially ... Read More

Attributes are the properties which describe an entity. Example The attributes of student entity are as follows − Roll number Name Branch Age Types of attributes The different types of attributes are as follows − Composite attribute It can be divided into smaller sub parts, each sub part can form an independent attribute. For example −     ... Read More

The network model was created to represent complex data relationships more effectively when compared to hierarchical models, to improve database performance and standards.It has entities which are organized in a graphical representation and some entities are accessed through several paths. A User perceives the network model as a collection of records in 1:M relationships.Given below is the pictorial representation of the network model in DBMS −FeaturesThe features of a Network Model are as follows −Ability to Merge Relationships − In this model, because of more relationships the data is more related. It has an ability to manage one-to-one relationships as ... Read More

It is a collection of concepts that can be used to describe the structure of a database. The structure of the database means data types, relationships and constraints that should hold the data nothing but it provides the necessary means to achieve the abstraction.A Model is basically a conceptualization between attributes and entities.There are basically three main data models in the Database Management System (DBMS), which are as follows −NetworkHierarchicalRelationalBut these days many new data models are being developed.Components of data modelThe data model can have three components which are as follows −Structural part − It consists of a set ... Read More

A set of functional dependencies (FD) F is said to cover another set of functional dependencies E if every FD in E is also in F closure; that is, if every dependency in E can be inferred from F.Alternatively, we can say E is covered by F. Two sets of functional dependencies E and F are equivalent if E+= F+. That is E is equivalent to F if E covers F and F covers E.To determine whether F covers E we calculate X+ with respect to F for each FD X->y in E and then check whether X+ includes the ... Read More

Decomposition means dividing a relation R into {R1, R2, ......Rn}. It is dependency preserving and lossless.Dependency preserving decompositionLet R is decomposed into {R1, R2, ...., Rn} with projected FD set {F1, F2, ......Fn}. This decomposition is dependency preserving if F+ ={F1 U F2 U.........Fn}+.ExampleLet the relation R{A, B, C, D, E} F:{AB->C, C->D, AB->D} R is decomposed to R1(A, B, C), R2(D, E). Prove decomposition is dependency preserving.SolutionF1={AB->C}F2={C->D}=> (F1 u F2) = {AB->C, C->D}AB+ under (F1 U F2) = {A, B, C, D} => AB->D is under (F1 U F2)F+ = (F1 U F2)+=> Decomposition is dependency preserving.Decomposition is not ... Read More