Chapter II: Data Models

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Chapter II: Data Models


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In this chapter, you will learn:In this chapter, you will learn:

Why data models are important About the basic data-modeling building blocks What business rules are and how they influence

database design How the major data models evolved How data models can be classified by level of

abstraction


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The Importance of Data ModelsThe Importance of Data Models

DATA MODELS

Relatively simple representations, usually graphical,of more complex real-world data structures.

Supported by powerful database design tools, have

made it possible to substantially diminish thepotential errors in database design.

It represents data structures and theircharacteristics, relation, constraints, andtransformations.


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MODEL Is an abstraction of more complex real-

world object or event

Its main function is to help you understandthe complexities of the real-world

environment.


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Data ModelData Model

Basic Building BlocksBasic Building Blocks1. Entity is anything (person, place, thing or event)

about which data are to be collected or stored. University -- Students, Faculty Members, Courses

Airlines -- Pilots, Aircraft, Routes, Suppliers2. Attribute is a characteristic of entity, equivalent of

the fields in file system Student-- Student Number, Name, GPA, Date of Enrollment, Data of

Birth, Home Address, Phone Number, Major

Aircraft-- Aircraft Number, Date of Last Maintenance, Total Hours

Flown, Hours Flown since Last Maintenance

3. Relationship describes association among entities


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3 types of relationship3 types of relationship

One-to-many (1:M) relationship

A painter paints many different painting, but each one of them ispainted by only one painter.

The painter (the one) is related to the painting (the many).

PAINTERpaints PAINTINGS as 1:M.

Many-to-many (M:N or M:M) relationship An employee may learn many job skills, and each job skill may be

learned by many employees.

EMPLOYEE learns SKILL as M:N

One-to-one (1:1) relationship

A retail companys management structure may require that each of its

stores be managed by a single employees. In turn, each store manager,who is an employee, manages only a single store.

EMPLOYEE manages STORE as 1:1.


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Relationships are bidirectional:

One CUSTOMER can generate manyINVOICEs.

Each of the manyINVOICEs is generated by

only one CUSTOMER.

4. Constraints is a restriction on the data.

Constraint helps to ensure data integrity.


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Business Rules

When DB designers are selecting ordetermining the entities, attributes, and

relationship that will be used in building a

data model, they may start by gaining a

thorough understanding of

What types of data are in an organization

How the data are used

In what time frames they are used


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BusinessR

ules Is a brief, precise, and unambiguous

description of a policy, procedure, or

principle within a specific organization.

Derived from a detailed description of an

organizations operations, help to create

and enforce actions within that

organizations environment.


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Example of business rules

A customer may generate many invoices.

An invoice is generated by only one customer

A training session cannot be scheduled for fewer than10 employees or for more than 30 employees.

Business rules establish entities, relationships andconstraints. For example, the first 2 business rulesestablished 2 entities, CUSTOMER and INVOICE,and 1:M relationship between those two entities.

The 3rd

business rule establishes a constraint: nofewer than 10 people and no more than 30 people; 2entities, EMPLOYEE and TRAINING; and arelationship between EMPLOYEE and TRAINING.


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Discovering Business Rules

MAIN SOURCE OF BUSINESS RULES:

Company managers

Policy makers

Department managers

Written documentation (e.g. companys

procedures, standards, or operations manuals)

Direct interviews with end user


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IMPORTANCE OF IDENTIFYINGAND DOCUMENTING

BUSINESS RULES: They help standardized the companys view of data

They can be a communications tool between users and

designers

They allow the designer to understand the nature, roleand scope of the data.

They allow the designer to understand business

processes

They allow the designer to develop appropriaterelationship participation rules and constraints and to

create an accurate data model.


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TRANSLATING BUSINESS RULES INTOTRANSLATING BUSINESS RULES INTO

DATA MODEL COMPONENTSDATA MODEL COMPONENTSGeneral rule:

A noun in a business rule will translate into

an entity in the model and a verb (active or

passive) associating nouns will translateinto a relationship among the entities.

For example:

A customer may generate many invoices

Nouns: CUSTOMER and INVOICES

Verb:may generate


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To properly identify the type of relationship, you shouldconsider that relationships are bidirectional; that is, they

go both ways.

For example, the business rule

a customer may generate many invoicesis complemented by the business rule

an invoice is generated by only one customer

In that case, the relationship is one-to-many (1:M).

CUSTOMER is the 1 side, and INVOICE is the many side.

As a general rule, to properly identify the relationship type,you should ask two questions:

How many instances of B are related to one instance of A?

How many instances of A are related to one instance of B?


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For example, you can assess the relationship

between student and class by asking twoquestions:

How many classes can one student enroll

in?

Answer: many classes

How many students can enroll in one class?

Answer: many students

Therefore, the relationship between student

and class is many-to-many (M:N).


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The Evolution of Data ModelsThe Evolution of Data Models


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Hierarchical Model

Hierarchical Model was developed in the

1960s to manage large amounts of data

complex manufacturing projects such as the

Apollo rocket that landed on the moon in1969.

Basic logical structure is represented by an

upside down treeIt was complex to implement, it was difficult to

manage, and it lacked structural independence.


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Network Model

Was created to represent complex data

relationships more effectively than the

hierarchical model.

Conference on Data Systems Languages

(CODASYL) created the Database Task

Group (DBTG) to help establish database

standards. The DBTG was charged to definestandard specifications for an environment

that would facilitate database creation and

data manipulation.


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Relational Data Model

Was introduced by E.F. Codd (of IBM) in

1970 in his landmark paper A Relational

Model of Data for Language Shared

Databanks

Represented a major breakthrough for both

users and designers.

Is implemented through a verysophisticated RDBMS.


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Table is a matrix consisting of a series of

row/column intersections.

Also called relations, are related to eachother through the sharing of a common

entity characteristics (value in column).

Relational diagram is a representation of

the relational databases entities, the

attributes within those entities, and the

relationship between those entities.


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The Entity Relationship Model


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Entity Relationship (ER) Model or ERM

first introduced by Peter Chen in 1976

it was the graphical representation of entities andtheir relationships in a database structure that

quickly became popular because it complementedthe relational data model concepts

are normally represented in an Entity RelationshipDiagram (ERD), which uses graphical

representations to model database components.


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ER Model components

Entity

represented in the ERD by a rectangle akaan entity box

the name of entity, a noun, is written in thecenter of the rectangle

a singular form and written in capitalletters

is described by a set of attributes thatdescribes particular characteristics of theentity


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Relationships are represented by a diamond connected

to the related entities through a

relationship line the name of the relationship, an active or

passive verb, is written inside the diamond.


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KEY

ENTITY Relationship

Mandatory One

Mandatory Many

Optional One

Optional Many

Cardinalities


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EXAMPLE: 1:M Relationship

a PAINTER can paintmany PAINTINGs.

each PAINTING is painted by one PAINTER.

PAINTER PAINTINGpaint

s


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EXAMPLE: M:N Relationship

an EMPLOYEE can learn many SKILLs.

each SKILL can be learned by many

EMPLOYEEs.

EMPLOYEE SKILLlearn

s


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EXAMPLE: 1:1 Relationship

an EMPLOYEE manages one STORE

each STORE is managed by one EMPLOYEE

EMPLOYEE STOREmanage

s


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Create an ER Diagram for a small furnituremanufacturing company, Pine ValleyFurniture.

This company can purchase items from anumber of different suppliers, who

then ship the items to themanufacturer. The items areassembled into products that are sold

to customers who order the products.Each order may include one or morelines corresponding to the productsappearing on that order.

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Chapter II: Data Models

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