Mba 664 database management
Download
1 / 19

MBA 664 Database Management - PowerPoint PPT Presentation


  • 147 Views
  • Uploaded on

MBA 664 Database Management. Dave Salisbury [email protected] (email) http://www.davesalisbury.com/ (web site). Evolution of the E-R Model. Basic E-R Model nearly 25 years old complex data relationships and new database technology have outgrown it in some respects Enhanced E-R Model

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'MBA 664 Database Management' - desma


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Mba 664 database management l.jpg

MBA 664Database Management

Dave Salisbury

[email protected] (email)

http://www.davesalisbury.com/ (web site)


Evolution of the e r model l.jpg
Evolution of the E-R Model

  • Basic E-R Model

    • nearly 25 years old

    • complex data relationships and new database technology have outgrown it in some respects

  • Enhanced E-R Model

    • a response to the shortcomings of the basic E-R model

    • not universally agreed upon in some respects

    • introduced the supertype/subtype relationship


Supertype subtype relationships l.jpg
Supertype/Subtype Relationships

  • Supertype (example: Employee)

    • a generic entity that has a relationship with one or more subtypes

  • Subtype (example: Manager)

    • a subgrouping of a supertype entity that is meaningful to an organization

    • shares all attributes of its supertype, but also has unique attributes of its own and/or :

    • has relationships with other entities distinct from those of other subtypes



The student example l.jpg
The student example

STUDENT

UNDERGRAD

STUDENT

GRAD

STUDENT


Two rules for when to use supertype subtypes l.jpg
Two Rules for When to Use Supertype/Subtypes

Use this type of relationship when either (or both) of the following are present:

  • When there are attributes that apply to some (but not all) of the instances of an entity type

  • When the instances of a subtype participate in a relationship unique to that subtype


Attribute inheritance l.jpg
Attribute Inheritance

  • “The property by which subtype entities inherit values of all attributes of the supertype.

  • This important property makes it unnecessary to include supertype attributes redundantly with the subtypes.”


Supertype subtype example 1 l.jpg

Name

City/State/Zip

SSN

EMPLOYEE

Telephone

HOURLY

EMPLOYEE

SALARIED

EMPLOYEE

CONSULTANT

Annual_Salary

Stock_Option

Contract_Number

Billing_Rate

Hourly_Rate

Supertype/Subtype Example 1



Two processes to develop supertype subtypes l.jpg

Generalization

The process of defining a more general entity type from a set of more specialized entity types

A “bottom-up” approach

Specialization

The process of defining one or more subtypes of a general entity based on distinguishing attri-butes or relationships

A “top-down” approach

Two Processes to Develop Supertype/Subtypes

Both approaches can be used together


Supertype subtype constraints l.jpg

Completeness

Addresses the question of whether an instance of a supertype must also be a member of at least one subtype

Disjointness

Addresses the question of whether an instance of a supertype may simultaneously be a member of two (or more) subtypes

Supertype/Subtype Constraints


Completeness constraint two possible rules l.jpg
Completeness Constraint: Two Possible Rules

  • Total Specialization Rule (Double-Line)

    • Specifies that each entity instance of the supertype must be a member of some subtype in the relationship (Example: all STUDENTS are either UNDERGRADUATE or GRADUATE students)

  • Partial Specialization Rule (Single-line)

    • Specifies that an entity instance of the supertype is allowed to not belong to any subtype (Example: FACULTY and STAFF are not the only possible members of the entity EMPLOYEE)


Completeness constraint l.jpg
Completeness constraint

Total specialization

Partial specialization


Disjointed constraint l.jpg

Can an entity instance simultaneously be a member of two or more subtypes?

Disjointed constraint

Disjoint rule

Overlap rule


Subtype discriminators l.jpg
Subtype discriminators

Attribute of the supertype whose value determines to which subtype an instance belongs




Supertype subtype hierarchy l.jpg

Arrangement of super- and subtypes where each subtype has only one supertype.

Supertype/subtype hierarchy


Another example l.jpg
Another example... only one supertype.


ad