Data Models

Model

is an abstraction of a more complex real

Data Model

a relatively simple representation, usually graphical, of more complex real

Data Modeling

the process of creating a specific data m odel for a determined problem domain

First step in Data Modeling

Designing a database

Basic Building blocks of all data models

entities, attributes, relationships, and constraints

Entity

anything (a person, place, thing, or an event) about which data are to be collected and stored

Attribute

characteristics of an entity

Relationship

describes an association among entities

Three types of Relationships:

One to Many
Many to Many
One to One

One to Many

one instance of an entity is allowd to be associated with several instances of other entity

Busimess Rules

describe the operations, definitions, and constraint that apply to an organization

Characteristics of a Good Business Rule

Declarative
Precise
Atomic
Expressible
Distinct
Consistent
Business Oriented

Declarative

a statement of policy, not how the policy is enforeced or conducted

Precise

it must have only on interpretation among all the interested people and its meaning must be clear

Atomic

One statement only; no part of the rule can stand on its own as a rule (Conjunction & Disjunction)

Expressible

Must be stated in a natural language but in a structured manner (remove unnecessary words)

Distinct

Must not be redundant; can refer other rules. It must not be similar to other rules

Consistent

Should not contain conflicting statement and should not contradict with other rules

Business Oriented

Use terms business people can understand. Only business people can modify or invalidate

Degrees of data abstraction

dictates how detail the model is

ANSI and Planning Committe

defined the framework for the data modeling based on the degress of data abstraction: External, Conceptual, Internal

External Model

ERD is complete. Based on the end user’s view of the data; usually focused on the business unit he/she belongs.

Conceptual Model

Done after external views. It is the bases for the identification and high

Internal

Done once a DBMS is selected. How the DBMS itself understands and stores the database. You take what you designed in the conceptual model and make sur eit fits the rules of DBMS, and internal sceme is written through mySQL