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.
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