ER key. Fig 1AttributesAttributes are units that describes the

ER DIAGRAMAn entity relationship diagram is based on the perception of the real world that consists of a collection of basic objects, called entities, and of relationships among these objects. E-R diagram represent the overall logical structure of a database. ER diagram is used in data modelling.Following are the important components that helps in designing an ER diagramEntityAn entity is an object that has its existence in the real world. It includes all those things about which data is collected. 

An entity can be a person, place, event, or object that is relevant to a given system.

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For example, if we say that a customer buys goods, it means customer and goods are entities.Generally, there are two type of entities Weak EntityAn entity that does not possess sufficient attributes to form a primary key is called weak entity.

It uses a foreign key combined with its attributed to form the primary key.

Strong EntityThe existence of the strong entity does not depend on the existence of the another entity in the schema. It has its own primary key.

                                                                                                                                                                    Fig 1AttributesAttributes are units that describes the characteristics or properties of entities. An entity can have as many attributes as necessary. In a database , entities are represented by tables and attributes by columns.In the following diagram the attributes of Student entity is listed in the table                                                                                                                                                         Fig 2
Various type of attributes areSimple and composite attributeSimple attributes are those attributes which can not be divided into subparts whereas composite attributes are those attributes which can be divided into subparts.

Single Valued and Multivalued attributesThe attributes which has a single value for a particular entity is called single valued attributes, whereas attributes which has a set of values for a specific entity is called multivalued attribute.Notations of E-R DiagramVarious symbols are used in designing an E-R diagram                                                                      
                                                                                                            Fig 3Relationship and Mapping constraints

A relationship describes how entities interact. Mapping constraint , express the number of entities to which another entity can be associated.There are four types of mapping constraint One to OneOne to ManyMany to One Many to Many                                                                                                          Fig 4KeysThe inetegrity of the information stored in a database is controlled by keys. A key or key field is a column value in a table that is used to either uniquely identify a row of data in table.Keys can be of different types:Super KeyA Super key is a set of one or more attributes that taken collectively, allow us to identify uniquely an entity in the entity set.Primary KeyA key that is chosen by the database designer as the principal means of identifying unique records within a table.
Candidate KeyA combination of one or more fields whose value uniquely identifies a record in a table , that is no two records in a table can have the same value.Foreign KeyA Foreign key is the combination  of one or more columns in a table at refrences a primary key in another table.

                     Fig 5                                                                                                                      Fig 6(Department_number as foreign key)Participation constraintTotal ParticipationEach entity is involved in the relationship. Total participation is representd by double lines.Partial participationNot all entities are involved in the relationship. Partial participation is represented by single lines.                                                                                                                                                    Fig 7ER Diagram template and ExampleCreating an ER diagram for a STUDENT database  Step1 – Analyse Given conditions or statements

‘Student attends class. Each class is divided into one or more sections. Each class will have its own specified subjects. Students have to attend all the subjects of the class that he attends’.

Step 2-Now we identify all the entities and their crossponding attributesER DIAGRAMAn entity relationship diagram is based on the perception of the real world that consists of a collection of basic objects, called entities, and of relationships among these objects. E-R diagram represent the overall logical structure of a database. ER diagram is used in data modelling.Following are the important components that helps in designing an ER diagramEntityAn entity is an object that has its existence in the real world. It includes all those things about which data is collected. 

An entity can be a person, place, event, or object that is relevant to a given system.

For example, if we say that a customer buys goods, it means customer and goods are entities.Generally, there are two type of entities Weak EntityAn entity that does not possess sufficient attributes to form a primary key is called weak entity.

It uses a foreign key combined with its attributed to form the primary key.

Strong EntityThe existence of the strong entity does not depend on the existence of the another entity in the schema. It has its own primary key.

                                                                                                                                                                    Fig 1AttributesAttributes are units that describes the characteristics or properties of entities. An entity can have as many attributes as necessary. In a database , entities are represented by tables and attributes by columns.In the following diagram the attributes of Student entity is listed in the table                                                                                                                                                         Fig 2
Various type of attributes areSimple and composite attributeSimple attributes are those attributes which can not be divided into subparts whereas composite attributes are those attributes which can be divided into subparts.

Single Valued and Multivalued attributesThe attributes which has a single value for a particular entity is called single valued attributes, whereas attributes which has a set of values for a specific entity is called multivalued attribute.Notations of E-R DiagramVarious symbols are used in designing an E-R diagram                                                                      
                                                                                                            Fig 3Relationship and Mapping constraints

A relationship describes how entities interact. Mapping constraint , express the number of entities to which another entity can be associated.There are four types of mapping constraint One to OneOne to ManyMany to One Many to Many                                                                                                          Fig 4KeysThe inetegrity of the information stored in a database is controlled by keys. A key or key field is a column value in a table that is used to either uniquely identify a row of data in table.Keys can be of different types:Super KeyA Super key is a set of one or more attributes that taken collectively, allow us to identify uniquely an entity in the entity set.Primary KeyA key that is chosen by the database designer as the principal means of identifying unique records within a table.
Candidate KeyA combination of one or more fields whose value uniquely identifies a record in a table , that is no two records in a table can have the same value.Foreign KeyA Foreign key is the combination  of one or more columns in a table at refrences a primary key in another table.

                     Fig 5                                                                                                                      Fig 6(Department_number as foreign key)Participation constraintTotal ParticipationEach entity is involved in the relationship. Total participation is representd by double lines.Partial participationNot all entities are involved in the relationship. Partial participation is represented by single lines.                                                                                                                                                    Fig 7ER Diagram template and ExampleCreating an ER diagram for a STUDENT database  Step1 – Analyse Given conditions or statements

‘Student attends class. Each class is divided into one or more sections. Each class will have its own specified subjects. Students have to attend all the subjects of the class that he attends’.

Step 2-Now we identify all the entities and their crossponding attributes

ER DIAGRAMAn entity relationship diagram is based on the perception of the real world that consists of a collection of basic objects, called entities, and of relationships among these objects. E-R diagram represent the overall logical structure of a database. ER diagram is used in data modelling.Following are the important components that helps in designing an ER diagramEntityAn entity is an object that has its existence in the real world. It includes all those things about which data is collected. 

An entity can be a person, place, event, or object that is relevant to a given system.

For example, if we say that a customer buys goods, it means customer and goods are entities.Generally, there are two type of entities Weak EntityAn entity that does not possess sufficient attributes to form a primary key is called weak entity.

It uses a foreign key combined with its attributed to form the primary key.

Strong EntityThe existence of the strong entity does not depend on the existence of the another entity in the schema. It has its own primary key.

                                                                                                                                                                    Fig 1AttributesAttributes are units that describes the characteristics or properties of entities. An entity can have as many attributes as necessary. In a database , entities are represented by tables and attributes by columns.In the following diagram the attributes of Student entity is listed in the table                                                                                                                                                         Fig 2
Various type of attributes areSimple and composite attributeSimple attributes are those attributes which can not be divided into subparts whereas composite attributes are those attributes which can be divided into subparts.

Single Valued and Multivalued attributesThe attributes which has a single value for a particular entity is called single valued attributes, whereas attributes which has a set of values for a specific entity is called multivalued attribute.Notations of E-R DiagramVarious symbols are used in designing an E-R diagram                                                                      
                                                                                                            Fig 3Relationship and Mapping constraints

A relationship describes how entities interact. Mapping constraint , express the number of entities to which another entity can be associated.There are four types of mapping constraint One to OneOne to ManyMany to One Many to Many                                                                                                          Fig 4KeysThe inetegrity of the information stored in a database is controlled by keys. A key or key field is a column value in a table that is used to either uniquely identify a row of data in table.Keys can be of different types:Super KeyA Super key is a set of one or more attributes that taken collectively, allow us to identify uniquely an entity in the entity set.Primary KeyA key that is chosen by the database designer as the principal means of identifying unique records within a table.
Candidate KeyA combination of one or more fields whose value uniquely identifies a record in a table , that is no two records in a table can have the same value.Foreign KeyA Foreign key is the combination  of one or more columns in a table at refrences a primary key in another table.

                     Fig 5                                                                                                                      Fig 6(Department_number as foreign key)Participation constraintTotal ParticipationEach entity is involved in the relationship. Total participation is representd by double lines.Partial participationNot all entities are involved in the relationship. Partial participation is represented by single lines.                                                                                                                                                    Fig 7ER Diagram template and ExampleCreating an ER diagram for a STUDENT database  Step1 – Analyse Given conditions or statements

‘Student attends class. Each class is divided into one or more sections. Each class will have its own specified subjects. Students have to attend all the subjects of the class that he attends’.

Step 2-Now we identify all the entities and their crossponding attributes

ER DIAGRAMAn entity relationship diagram is based on the perception of the real world that consists of a collection of basic objects, called entities, and of relationships among these objects. E-R diagram represent the overall logical structure of a database. ER diagram is used in data modelling.Following are the important components that helps in designing an ER diagramEntityAn entity is an object that has its existence in the real world. It includes all those things about which data is collected. 

An entity can be a person, place, event, or object that is relevant to a given system.

For example, if we say that a customer buys goods, it means customer and goods are entities.Generally, there are two type of entities Weak EntityAn entity that does not possess sufficient attributes to form a primary key is called weak entity.

It uses a foreign key combined with its attributed to form the primary key.

Strong EntityThe existence of the strong entity does not depend on the existence of the another entity in the schema. It has its own primary key.

                                                                                                                                                                    Fig 1AttributesAttributes are units that describes the characteristics or properties of entities. An entity can have as many attributes as necessary. In a database , entities are represented by tables and attributes by columns.In the following diagram the attributes of Student entity is listed in the table                                                                                                                                                         Fig 2
Various type of attributes areSimple and composite attributeSimple attributes are those attributes which can not be divided into subparts whereas composite attributes are those attributes which can be divided into subparts.

Single Valued and Multivalued attributesThe attributes which has a single value for a particular entity is called single valued attributes, whereas attributes which has a set of values for a specific entity is called multivalued attribute.Notations of E-R DiagramVarious symbols are used in designing an E-R diagram                                                                      
                                                                                                            Fig 3Relationship and Mapping constraints

A relationship describes how entities interact. Mapping constraint , express the number of entities to which another entity can be associated.There are four types of mapping constraint One to OneOne to ManyMany to One Many to Many                                                                                                          Fig 4KeysThe inetegrity of the information stored in a database is controlled by keys. A key or key field is a column value in a table that is used to either uniquely identify a row of data in table.Keys can be of different types:Super KeyA Super key is a set of one or more attributes that taken collectively, allow us to identify uniquely an entity in the entity set.Primary KeyA key that is chosen by the database designer as the principal means of identifying unique records within a table.
Candidate KeyA combination of one or more fields whose value uniquely identifies a record in a table , that is no two records in a table can have the same value.Foreign KeyA Foreign key is the combination  of one or more columns in a table at refrences a primary key in another table.

                     Fig 5                                                                                                                      Fig 6(Department_number as foreign key)Participation constraintTotal ParticipationEach entity is involved in the relationship. Total participation is representd by double lines.Partial participationNot all entities are involved in the relationship. Partial participation is represented by single lines.                                                                                                                                                    Fig 7ER Diagram template and ExampleCreating an ER diagram for a STUDENT database  Step1 – Analyse Given conditions or statements

‘Student attends class. Each class is divided into one or more sections. Each class will have its own specified subjects. Students have to attend all the subjects of the class that he attends’.

Step 2-Now we identify all the entities and their crossponding attributes