er diagrams presentation

ER Diagrams

ER DiagramsAcropolis Institute of Technology and Research

To be discussed:-EntityAttributeTypes of AttributeRelationshipER Diagram Representation GeneralizationSpecializationInheritanceCodds 12 RuleRelational Data ModelER Model to Relational Model

EntityAn entity can be a real-world object, either animate or inanimate, that can be easily identifiable. Example : School Database TeachersStudentsClassesCourses offeredEntity setAn entity set is a collection of similar types of entities. An entity set may contain entities with attribute sharing similar values.

AttributesEntities are represented by means of their properties, calledattributes. All attributes have values. Example : Student :- Name, Class, Age

Types of Attributes

Simple attribute Simple attributes are atomic values, which cannot be divided further. For example, a student's phone number is an atomic value of 10 digits.

Composite attribute example, a student's complete name may have first_name and last_name.

Types of Attributes Continue..Derived attribute example, average_salary in a department should not be saved directly in the database, instead it can be derived.

For another example, age can be derived from data_of_birth.

Single-value attribute Single-value attributes contain single value. example : Social_Security_Number.

Multi-value attribute Multi-value attributes may contain more than one values.

Example: a person can have more than one phone number, email_address, etc.

RelationshipThe association among entities is called relationship.

Ex: Employee works_at departmentEx: Student enrolls in a course

Relationship SetA set of relationships of similar type is called a relationship set. Like entities, a relationship too can have attributes. These attributes are calleddescriptive attributes.

Mapping cardinalities

Cardinalitydefines the number of entities in one entity set, which can be associated with the number of entities of other set via relationship set.

One to oneOne to manyMany to oneMany to many

One to One

Entity set A Entity set B

One to many


Many to one


Many to manyEntity set A Entity set B

ER Diagram Representation

Entity

Attributes

TeacherStudentClassesStudentNameRollBirth_Date

ER Diagram Representation Continue

Composite

StudentNameRollBirth_DateLastFirst

ER Diagram Representation ContinueMultivalued

StudentNameRollBirth_DateLastFirstPhone_No

ER Diagram Representation ContinueDerived

StudentNameRollBirth_DateLastFirstPhone_No

Age

ER Diagram Representation ContinueRelationship Binary Relationship and Cardinality

When two entities participate in a relationship then it is called Binary Relationship.

Cardinality is the number of instance of an entity from a relation that can be associated with the relation.

ER Diagram Representation ContinueOne to One (1:1)

1 1

Example : Person PassportStudent Roll-No

RelationshipEntityEntity

ER Diagram Representation ContinueOne to Many (1:N)

1 N

Example : Mother- ChildrenStudent - Address


ER Diagram Representation ContinueMany to One (N:1)

N 1

Example : Students - Teacher


ER Diagram Representation ContinueMany to One (M:N)

M N

Example : - Books - Authors


ER Diagram Representation ContinueParticipation Constraint

Total participation Partial participation


The ER Model has the power of expressing database entities in a conceptual hierarchical manner. As the hierarchy goes up, it generalizes the view of entities, and as we go deep in the hierarchy, it gives us the detail of every entity included.

Going up in this structure is called Generalization Reverse is called Specialization

Generalization and Specialization

GeneralizationPigeonBirdsPeacockSparrow

SpecializationPersonTeacherStudent

IS A

Inheritance

PersonNameGenderBirth_DateTeacherStudentEMP_IDRollIS A

Relational Data ModelRelational data model is the primary data model, which is used widely around the world for data storage and processing.

ConceptsToupleRelation InstanceRelation SchemaRelation keyAttribute domain

Key ConstraintsKey constraints

Primary Key

Foreign Key

Candidate Key

Alternate Key

Key Constraints .Key constraints force that in a relation with a key attribute, no two tuples can have identical values for key attributes.a key attribute can not have NULL values.

Domain constraintsEvery attribute is bound to have a specific range of values.Example : Age can not be negativeReferential integrity constraints

Key Constraints .Referential integrity constraintsEvery relation has some conditions that must hold for it to be a valid relation. These conditions are calledRelational Integrity Constraints.

I If a relation refers to a key attribute of a different or same relation, then that key element must exist.

ER model to Relational ModelER model EntityAttributes

Mapping EntityCreate table for each entity.Entity's attributes should become fields of tables with their respective data types.Declare primary key.

ER model to Relational ModelMapping Relationship

Create table for a relationship.Add the primary keys of all participating Entities as fields of table with their respective data types.If relationship has any attribute, add each attribute as field of table.Declare a primary key composing all the primary keys of participating entities.Declare all foreign key constraints.

ER model to Relational ModelMapping Weak entity set

Create table for weak entity set.Add all its attributes to table as field.Add the primary key of identifying entity set.Declare all foreign key constraints.

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