Modeling Data in the Organization Muhammad Nasir

Contents Business rule, Entity Relationship model (E- R model), entity-relationship Diagram (E-R diagram), Entity, Entity Type, Entity Instance, Strong Entity Type, Weak Entity Type, Identifying Owner Identifying Relationship, Attribute, Required Attribute, Optional Attribute Composite Attribute, Simple Attribute, Multi- valued Attribute, Derived Attribute, Identifier

Entity-Relationship Model (E-R model) A logical representation of the data for an organization or for a business area, using entities for categories of data and relationships for associations between entities

Entity-relationship diagram (E-R diagram, or ERD) A graphical representation of an entity- relationship model

Sample ERD

E-R Model Notation

Business rule A statement that defines or constrains some aspect of the business It is intended to assert business structure or to control or influence the behavior of the business

Business Rule “A student may register for a course only if he or she has successfully completed the prerequisites for that course.” “A preferred customer qualifies for a 10 percent discount, unless he has an overdue account balance.”

Data Modeling Entity type A collection of entities that share common properties or characteristics Entity instance A single occurrence of an entity type

Data Modeling Strong entity type An entity that exists independently of other entity types Weak entity type An entity type whose existence depends on some other entity type

Data Modeling

Identifying owner The entity type on which the weak entity type depends Identifying relationship The relationship between a weak entity type and its owner.

Data Modeling Attribute A property or characteristic of an entity or relationship type that is of interest to the organization

Data Modeling Required attribute An attribute that must have a value for every entity (or relationship) instance with which it is associated. Optional attribute An attribute that may not have a value for every entity (or relationship) instance with which it is associated.

Data Modeling

Composite attribute An attribute that has meaningful component parts (attributes) Simple (or atomic) attribute An attribute that cannot be broken down into smaller components that are meaningful to the organization

Data Modeling

Multi-valued attribute An attribute that may take on more than one value for a given entity (or relationship) instance.

Data Modeling

Derived attribute An attribute whose values can be calculated from related attribute values.

Data Modeling Identifier An attribute (or combination of attributes) whose value distinguishes instances of an entity type. Composite identifier An identifier that consists of a composite attribute.

Data Modeling

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