Data is collected and stored on personal computers which are small and easily manageable. The data is generally used by the same department of an organization and is accessed by a small group of people.

In a Relationship, Participation constraint specifies the existence of an entity when it is related to another entity in a relationship type. It is also called minimum cardinality constraint.This constraint specifies the number of instances of an entity that can participate in a relationship type.There are two types of Participation constraint −Total ParticipationEach entity in the entity set is involved in at least one relationship in a relationship set i.e. the number of relationship in every entity is involved is greater than 0.Consider two entities Employee and Department related via Works_For relationship. Now, every Employee works in at least one ... Read More

In Ternary relationship three different Entities takes part in a Relationship.Relationship Degree = 3For Example: Consider a Mobile manufacture company.Three different entities involved:Mobile - Manufactured by company. Part - Mobile Part which company get from Supplier. Supplier - Supplier supplies Mobile parts to Company.Mobile, Part and Supplier will participate simultaneously in a relationship. because of this fact when we consider cardinality we need to consider it in the context of two entities simultaneously relative to third entity.Cardinality in Ternary RelationshipSay for a given instance of Supplier and an Instance of Part, can that supplier supply that particular part for multiple Mobile models.Example ... Read More

A Binary Relationship is the relationship between two different Entities i.e. it is a relationship of role group of one entity with the role group of another entity.There are three types of cardinalities for Binary Relationships −1. One-to-One2. One-to-many3. Many-to-ManyOne-to-OneHere one role group of one entity is mapped to one role group of another entity. In simple terms one instance of one entity is mapped with only one instance of another entity.In this type the primary key of one entity must be available as foreign key in other entity.For example − consider two entities Person and Driver_License.Person has the information about ... Read More

A One-to-Many Unary Relationship is the association with the same entity between the same instances represented by different role groups.Consider the relationship between Managers and Employees.The two different Roles in this relationship are- Managers and Employees. Only few Employees take the role of Managers within an organization while everyone working for an organization is an Employee.One Manager manages multiple Employees and each Manager is also an Employee. One-to-Many Optional-MandatoryEach instance of one role group must participate in the relationship while instance of other role group can optionally participate in the relationship. The Role of Manager satisfies the optional participation as there are ... Read More

A One-to-One Unary Relationship is the association with the same entity between the same instances represented by same role group.Above figure represents a set of married persons with the relationship MARRIED_TO. Each person is married to only one and only one person in the group.In One-to-One Unary we have three cases available −Mandatory-MandatoryOptional-OptionalOptional-Mandatory or Mandatory-OptionalMandatory-MandatoryEach instance of the role group must fully participate in the relationship. In the above example a Person is married to one and only one Person.Optional-OptionalIn this case the participation of a instance within a role group is optional i.e. the participation is not mandatory.In the ... Read More

In 6NF, the relation variable is decomposed into irreducible components. A relation is in 6NF, only if, It is in 5NF, and every join dependency on the relation is trivialLet us see an example −Enrollment_NoNameMarksThe possible join dependencies for the above would be −{Enrollment_No, Marks}{Enrollment_No, Name}In Sixth Normal Form (6NF), it would be decomposed to −Enrollment_NoNameEnrollment_No MarksLet us see another example −Student_IDStudent_FirstNameStudent_LastNameMarksS01TomAlter90S02JacobWatson80S03HarrySmith85Let us decompose the table −Student_IDStudent_FirstNameS01TomS02JacobS03HarryStudent_IDStudent_LastNameS01AlterS02WatsonS03SmithStudent_IDMarksS0190S0280                     S03                   85Now the above tables are in 6NF, but as you can guess on your know that ... Read More

Many users consider Primary Key as Unique Key, since both uniquely identify a table, but Unique Key is different from Primary Key. Unique Key accepts null values and Primary Key cannot have null.Let us compare Primary Key and Unique Key and understand its concept −UsageA Unique Key is used to prevent duplicate values in a column. Primary Key provided uniqueness to a table.NULL ValuesA primary key cannot accept NULL values; this makes Primary Key different from Unique Key, since Unique Key allows one value as NULL value.VolumeA table can only have a single Primary Key, whereas a Unique Key can ... Read More

RDMS Terminologies include Database, Table, Columns, etc. Let us see them one by one −DatabaseDatabase is a collection of tables like , , etc.TableA table is a collection of rows and columns , for example, StudentIdStudentNameStudentRank052Tom1035David2077John3ColumnColumn is in a table −RowRow is also called a tuple in RDBMS. A relation in a database has rows and columns.Primary KeyEvery table has one Primary key and cannot have null values.For example, ProjectID is a primary key in Project Table, since it uniquely identifies the project:ProjectIDProjectNameP01Cluster Grouping SystemP02Hospital Management SystemForeign KeyIf you want to link two tables, use Foreign Key.For example, Employee table has DEPT_ID ... Read More

A Foreign Key creates a link between tables. It references the primary key in another table and links it.For example, the DeptID in the Employee table is a foreign key −EmpIDEmpNameEmpAgeDeptIDDeptIDDeptNameDeptZoneThe DeptID in the Department table is a Primary Key in the Department Table.The DeptID in the Employee table is a Foreign Key in the Employee Table.The below figure represents the same −Above, you can see our two tables. The Foreign Key of the Employee table is the Primary Key of the Department table.