er modeling chittaranjan pradhan database management · er modeling chittaranjan pradhan overview...

ER Modeling

Chittaranjan Pradhan

Overview of theDatabase DesignProcess

Entity-Relationship(ER)Model

Attribute Types

Mapping CardinalityRepresentation

5.1

Database ManagementSystem 5ER Modeling

Chittaranjan PradhanSchool of Computer Engineering,

KIIT University

ER Modeling




Attribute Types


5.2

Overview of the Database Design Process

• The initial phase of database design is to characterize fullythe data needs of the prospective database users. Itusually involves in textual description

• Next, the designer chooses a data model and, by applyingthe concepts of the chosen data model, translates theserequirements into a conceptual schema of the database.The ER model is typically used to represent theconceptual design

• The designer reviews the schema to confirm that all datarequirements are satisfied and are not in conflict with oneanother

• At this stage of conceptual design, the designer canreview the schema to ensure it meets all the functionalrequirements

ER Modeling




Attribute Types


5.3

Overview of the Database Design Process...

• The process of moving from an abstract data model to theimplementation of the database proceeds in two finaldesign phases:

• In the logical design phase, the designer maps thehigh-level conceptual schema onto the implementation datamodel of the database system that will be used. Theimplementation data model is typically the Relational datamodel

• Finally, the designer uses the resulting system-specificdatabase schema in the subsequent physical-design phase,in which the physical features of the database are specified

ER Modeling




Attribute Types


5.4

Entity-Relationship(ER) Model

Entity-Relationship(ER) Model

The ER model was developed to facilitate the database designby allowing specification of an enterprise schema thatrepresents the overall logical structure of a database. The ERmodel is very much useful in mapping the meaning andinteractions of real-world enterprises onto a conceptualschema

Entities

An entity is a thing or object in the real world that isdistinguishable from all other objects, i.e. an entity is an objectof interest to the end user. The set of similar types of entities iscalled entity set; which is represented by a rectanglecontaining the entity set’s name. The entity set name, a noun,is usually written in all capital letters

ER Modeling




Attribute Types


5.5

Entity-Relationship(ER) Model...

Attributes

Attributes are characteristics of entities. Attributes arerepresented by ovals and are connected to the respectiveentity set with lines. In the conceptual modeling, the value of anattribute comes from a domain of possible values

Relationships

In modeling, the association between entities are referred to asrelationship. The relationship name is a verb. A relationship setis a set of relationships of the same type. Relationship sets arerepresented by diamonds and are connected to the participantentity sets

NULL Values

An attribute takes a NULL value when an entity doesn’t have avalue for it. The NULL values may indicate not applicable, i.e.the value doesn’t exist for the entity. NULL can also designatethat an attribute value is unknown. An unknown value may beeither missing or not known. NULL value is an entry in all thedomains

ER Modeling




Attribute Types


5.6

Attribute Types

Simple and Composite attributes

An attribute that has a discrete factual value and cannot bemeaningfully subdivided is called an atomic or simpleattribute.On the other hand, a composite attribute can bemeaningfully subdivided into smaller subparts (i.e. simpleattributes) with independent meaning

ER Modeling




Attribute Types


5.7

Attribute Types...

Single-valued and Multi-valued attributes

Most attributes have a single value for a particular entity andare referred to as single-valued attribute. However, attributesthat can have more than one value are known as multi-valuedattributes. It is represented by double oval

ER Modeling




Attribute Types


5.8

Attribute Types...

Stored and Derived attributes

The attribute with independent existence is called as storedattribute where as the attribute, whose value is depending onother stored attribute, is called as derived attribute. The derivedattribute is represented by the dotted oval

ER Modeling




Attribute Types


5.9

Attribute Types...

Descriptive attributes

A relationship may also have attributes called descriptiveattributes for representing the description about the association

ER Modeling




Attribute Types


5.10

Mapping Cardinality Representation

M:N relationship

An entity in A is associated with any number (zero or more) ofentities in B and vice versa

ER Modeling




Attribute Types


5.11

Mapping Cardinality Representation...

1:M relationship

An entity in A is associated with any number (zero or more) ofentities in B; an entity in B, however, is associated with nomore than 1 entity set of A

ER Modeling




Attribute Types


5.12

Mapping Cardinality Representation...

1:1 relationship

An entity in A is associated with no more than 1 entity of B; andan entity in B is associated with no more than 1 entity of A

er modeling chittaranjan pradhan database management · er modeling chittaranjan pradhan overview...

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