Multivalued dependency (MVD) is having the presence of one or more rows in a table. It implies the presence of one or more other rows in that same table. A multivalued dependency prevents fourth normal form. A multivalued dependency involves at least three attributes of a table.It is represented with a symbol "->->" in DBMS.X->Y relates one value of X to one value of Y.X->->Y (read as X multidetermines Y) relates one value of X to many values of Y.A Nontrivial MVD occurs when X->->Y and X->->z where Y and Z are not dependent are independent to each other. Non-trivial ... Read More

BCNF (Boyce Codd Normal Form) is the advanced version of 3NF. A table is in BCNF if every functional dependency X->Y, X is the super key of the table. For BCNF, the table should be in 3NF, and for every FD. LHS is super key.ExampleConsider a relation R with attributes (student, subject, teacher).StudentTeacherSubjectJhansiP.NareshDatabasejhansiK.DasCsubbuP.NareshDatabasesubbuR.PrasadCF: { (student, Teacher) -> subject (student, subject) -> Teacher Teacher -> subject}Candidate keys are (student, teacher) and (student, subject).The above relation is in 3NF [since there is no transitive dependency]. A relation R is in BCNF if for every non-trivial FD X->Y, X must be a key.The ... Read More

A relation is in 3NF when it is in 2NF and there is no transitive dependency or a relation is in 3NF when it is in 2NF and all non-key attributes directly depend on candidate key.Third normal form (3NF) is the third step in normalizing a database and it builds on the first and second normal forms, 1NF and 2NF.3NF states that all column references in referenced data that are not dependent on the primary key should be removed. Another way of putting this is that only foreign key columns should be used to reference another table, and no other ... Read More

A relation is in 3NF when it is in 2NF and there is no transitive dependency or a relation is in 3NF, when it is in 2NF and all non-key attributes directly depend on candidate key.ExampleConsider a relation student (rollno, game, feestructure)RollnoGameFeestructure1Basketball5002Basketball5003Basketball5004Cricket6005Cricket6006Cricket6007Tennis400F − {rollno -> game, rollno -> feestructure, game -> fee} Rollno+= {rollno, game, feestructure} => rollno is primary keyThe above student table is in 1NF because there are no multivalue attributes.Student table is also in 2NF because all non-key attributes are fully functional dependent on the primary key (rollno). But the table is not in 3NF because there ... Read More

Let us begin by understanding what a functional dependency is in the database management system (DBMS).Functional DependencyFunctional dependency refers to the relation of one attribute of the database to another. With the help of functional dependency, the quality of the data in the database can be maintained.The symbol for representing functional dependency is -> (arrow).Example of Functional DependencyConsider the following table.Employee NumberNameCitySalary1bobBangalore250002LuckyDelhi40000The details of the name of the employee, salary and city are obtained by the value of the number of Employee (or id of an employee). So, it can be said that the city, salary and the name attributes ... Read More

The overall design of the database is called database schema. Schema will not be changed frequently. It is the logical structure of a database. It does not show the data in the database.The schema is pictorially represented as follows −Types of SchemaThe different types of schemas are as follows −Physical schema − It is a database design at the physical level.It is hidden below the logical schema and can be changed easily without affecting the application programs.Logical schema − It is a database design at the logical level. Programmers construct applications using logical schema.External − It is schema at view ... Read More

ProblemDraw of ER model for company considering the following constraints −In a company, an employee works on many projects which are controlled by one department.One employee supervises many employees.An employee has one or more dependents.One employee manages one department.SolutionFollow the steps given below to draw an ER model for the company −Step 1 − Identify the entity setsThe entity set has multiple instances in a given business scenario.As per the given constraints the entity sets are as follows:EmployeeDepartmentProjectDependentStep 2 − Identify the attributes for the given entitiesEmployee − The relevant attributes are name, ssn, sex, address, salary.Department − The relevant ... Read More

ProblemDraw an ER model for library management application considering the following constraints −In a library multiple students can enroll.Students can become a member by paying an appropriate fee.The books in the library are identified by a unique ID.Students can borrow multiple books from subscribed libraries.SolutionFollow the steps given below to draw an ER model for the library management application −Step 1 − Identify the entity setsThe entity set has multiple instances in a given business scenario.As per the given constraints the entity sets are as follows −BookPublisherMemberSectionGranterStep 2 − Identify the attributes for the given entitiesBook − The relevant attributes ... Read More

ProblemDraw an ER model of the Banking database application considering the following constraints −A bank has many entities.Each customer has multiple accounts.Multiple customers belong to a single branch.Single customer can borrow multiple loans.A branch has multiple employees.SolutionFollow the steps given below to draw an ER model of the Banking database application −Step 1 − Identify the entity setsThe entity set has multiple instances in a given business scenario.As per the given constraints the entity sets are as follows −CustomerAccountAccountLoanLoanStep 2 − Identify the attributes for the given entitiesCustomer − the relevant attributes are customerName, CustomerID, address.Account − The relevant attributes ... Read More

ProblemDrawing of ER model of university database application considering the constraints −A university has many departments.Each department has multiple instructors (one person is HOD). Here the HOD refers to the head of department.An instructor belongs to only one department.Each department offers multiple courses, each subject is taught by a single instructor.A student may enroll for many courses offered by different departments.SolutionFollow the steps given below to draw an Entity Relationship (ER) diagram for a University database application −Step 1 − Identifying the entity sets.The entity set has multiple instances in a given business scenario.As per the given constraints the entity ... Read More