How to Make an ERD

Cardinality Notations

Cardinality specifies how many instances of an entity relate to one instance of another entity.

Ordinality is also closely lined to cardinality. While cardinality specifies the occurances of a relationship, ordinality describes the relationship as either mandatory or optional. In other words, cardinality specifies the maximum number of relationships and ordinality specifies the absolute minimum number of relationships. When the minimum number is zero, the relationship is usually called optional and when the minimum number is one or more, the relationship is usually called mandatory.

There are many notation styles that express cardinality and they are all supported by SmartDraw.

Data model- is an abstract model that documents and organize the business data for communication between team members and is use as a plan for developing applications, specifically how data is stored and access.(software engineering)*dapat naiintindihan ng lahat*it should be software and hardware independent.

Entity- example: CLASS,STUDENT,INSTRUCTOR

Attributes- example: -SECTION,NAME,NAME -YEAR, ,GENDER,ADDRESS -SUBJECT,AGE

Relationship- class--student--instructor *one-to-many: sa isang klase,maraming student *many-to-many: *one-to-one:

Constrain-

Business Rules-Procedure,Policies, and Principles.

Business Rules >>>>>Conceptual Data Model

*sources of Business rules**

EVOLUTION OF DATA MODELS* *HIERARCHICAL MODE- "UP-SIDE-DOWN TREE"

*NETWORK MODEL *SCHEMA..........

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ERD - represents the conceptual database as viewed by the end user.3 components (entities,attributes and relationship)

*Entities-is represented by a RECTANGLE containing the entity's name,a noun,is written in capital letters.

*Attributes-are represented by OVALS connected to the entity w/a line >domain-are attribute's set of possible values >Primary Key-are key attributes underline in the ER diagram.

>Composite key-are primary key's composed of morethan one attribute

>Composite Attribute-attributes that can be further subdivided to yield additional attributes.

>simple attribute-cannot be subdivided.

>single-valued attribute- can have only single value.

>Multivalued attributes-have many value.

*Relationship- is an association between entities,represented by a DIAMOND SHAPE.

>Relationship's Degree- indicate's the no. of associated entities or participants.

>Unary relationship-exists when an association is maintained with a single entity.

>Binary relationship-exists when two entities are associated.

> Ternary relationship-exists when two entities are associated.

CONNECTIVITY-is used to describe the relationship classification ,The ERD indicates the relationship's connectivity by planning I,M,N near related entities.

CARDINALITY-express the specific number of entity occurances with one occurance of related entity.

Relationship participation(optional and mandatory)

*optional- if one entity occurance does not require a corresponding entity occurance in a particular relationship(is shown by darwing a SMALL CIRCLE on the side of the optional entity.)

>WEAK ENTITY- is existence-dependent,that is it cannot exist w/o the entity w/c it has relationship.

- has primary key that is partially or totally derived from parent entity in the relationship.

- indicate by a double rectangle.

>RECURSIVE ENTITY-is on in w/c relationship can exist between occurance of the same entity set.

>COMPOSITE ENTITY-are bridge entity ,composed of the primary key of each of the entity to be connected . represented by a DIAMOND WITH A RECTANGLE.ENTITY SUPERTYPES &

SUBTYPES(generalization hierarchy)

*Supertype-contains the SHARED attributes (high-level)

*Subtype-contains UNIQUE attributes (low-level) Disjoint realtionship- supertype entity set related to unique and nonoverlapping (disjoint) subtype entity set.
-represented by ONE SYMBOL G.

SmartDraw download link:http://download.cnet.com/SmartDraw-2010/3000-2075_4-10002466.html

SmartDraw IDE

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