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

It is the relationship between the instances of two different entity types. Two entities will participate in the relationship.ExamplePerson and events are two different entity types which are related by using the relationship called “attends”.Mapping ER diagram with binary relationshipMapping one to many relationshipExampleHere, Create two tables for two entities.Primary key of one side relation is a foreign key for many side relations.One side relation is customer and many side relations is Order.The primary key cutomerID of the customer is a foreign key of order.The equivalent relations for the above ER diagram are as follows −One-one, many-one, many-many can be ... Read More

The attributes that cannot be divided into sub-parts are called simple attributes. The attributes which can be divided into sub-parts are called composite attributes.ExampleBalance, account number are simple attributesName, address is called composite attributesLet’s consider an example of how to convert Entity Relationship (ER) model of composite attribute to Relational model.Methods for mappingName of relation = Entity set of ER diagramName of column = Attribute of ER diagramExampleIn this example, Name of the relation =studentName of columns=StdID, name, BranchThe equivalent relation for the above ER diagram is −StudentStdIDNameBranchNow apply this technique for Mapping ER diagram with a composite attribute as ... Read More

Key is a data item which is used to identify a record or a value used to identify a record in a database is called a key. It helps uniquely to identify an entity from an entity set.Key allows us to identify a set of attributes that make them sufficient to distinguish entities from each other.ExampleAccount number, employee number, customer number are used as a key field because they specifically identify a record stored in a database.Foreign KeyIn a relation, the column whose data values correspond to the values of a key column in another relation is called a foreign ... Read More

Key is a data item which is used to identify a record or a value used to identify a record in a database is called a key. It helps uniquely to identify an entity from an entity set.Key allows us to identify a set of attributes that make them sufficient to distinguish entities from each other.ExampleAccount number, employee number, customer number are used as key fields because they specifically identify a record stored in a database.Different types of keysThe different types of keys in the database management system (DBMS) are as follows −Primary keySuper keyCandidate keyAlternate keyArtificial keyForeign keyPrimary, super, ... Read More

Key is a data item which is used to identify a record or a value used to identify a record in a database is called a key. It helps uniquely to identify an entity from an entity set.Key allows us to identify a set of attributes that make it sufficient to distinguish entities from each other.ExampleAccount number, employee number, customer number are used as key fields because they specifically identify a record stored in a database.Different types of keysThe different types of keys in the database management system (DBMS) are as follows −Primary keySuper keyCandidate keyAlternate keyArtificial keyForeign keyPrimary, super, ... Read More

The number of entity types which took part in the entity relationship is called the degree of relationships.There are three different types of degree of relationships, they are as follows −Unary relationshipBinary relationshipTernary relationshipUnary relationshipIt is the relationship between the instances of a single entity type. It is also called a recursive relationship.ExampleA person is married is a one-to-one relationship between the instances of Person entity type of unary relationship.Binary relationshipIt is the relationship between the instances of two different entity types. Two entities will participate in the relationship.For ExamplePerson and events are two different entity types which are related ... Read More

In the view of databases, cardinality refers to the uniqueness of data values that are contained in a column. High cardinality is nothing but the column contains a large percentage of totally unique values. Low cardinality is nothing but the column which has a lot of “repeats” in its data range.Cardinality between the tables can be of type one-to-one, many-to-one or many-to-many.Mapping CardinalityIt is expressed as the number of entities to which another entity can be associated via a relationship set.For binary relationship set there are entity set A and B then the mapping cardinality can be one of the ... Read More

Constraints are used for modeling limitations on the relations between entities.There are two types of constraints on the Entity Relationship (ER) model −Mapping cardinality or cardinality ratio.Participation constraints.Mapping CardinalityIt is expressed as the number of entities to which another entity can be associated via a relationship set.For the binary relationship set there are entity set A and B then the mapping cardinality can be one of the following −One-to-oneOne-to-manyMany-to-oneMany-to-manyOne-to-one relationshipAn entity set A is associated with at most one entity in B and an entity in B is associated with at most one entity in A.One-to-many relationshipAn entity set A ... Read More

A database model is a logical structure of a database, which contains the relationships and constraints that determine about how data is stored and accessed. The individual database models are designed based on the rules and concepts. Most data models can be represented by an accompanying database diagram.Types of database modelsThere are so many database models, but most used database models are −Hierarchical database modelRelational modelNetwork modelObject-oriented database modelThe major differences between the hierarchical, network and the relational models are as follows −Hierarchical ModelNetwork ModelRelational ModelOne to many or one to one relationship.Allowed the network mode to support many to ... Read More