Supertipuri si subtipuri

Supertipuri si subtipuri

Au aparut deoarece unele instante ale unei entitati au atribute si/sau relatii pe care nu le au alte instante ale aceleiasi entitati.

Ex:

payment type (check, cash, credit).

Toate tipurile de plata au cateva atribute in comun: data platii, suma de plata si altele.

Insa

doar plata cu cardul de credit are suplimentar atributul "numaru card"

doar pentru plata cu cardul de credit  si platile prin cec trebuie sa stim ce comparator a facut plata

animal (vertebrate, nevertebrate),

Vertebratele - au coloana vertebrala si pot fi impartite in: pasari, mamifere, reptile

Nevertebratele sunt animale fara coloana vertebrala (cum ar fi viermii pamant)

food orders (eat in, to go),

grocery bags (paper, plastic),

examen (quiz, midterm, final)

6. ANGAJAT (Nume, Prenume,.): putem defini subtipuri pentru a deservi activitati specifice: SECRETARA, TEHNICIAN, INGINER. Fiecare subtip mosteneste atributele tipului de baza ANGAJAT. Subtipul mai contine si atribute specifice:

a. SECRETARA (Viteza redactare);

b. TEHNICIAN (Grad, Calificare);

c. INGINER (Specialitate).

Uneori are sens sa divizam o entitate in subtipuri. Acesta poate fi cazul cand un grup de instante au proprietati speciale, cum ar fi ca atributele sau relatii care  exista numai pentru acel grup.

In acest caz entitatea este numita supertip si fiecare grup este numit subtip.

Un subtip

Mosteneste toate atributele, relatiile unui supertip

Poate avea propriile sale atribute si relatii

Este desenat in supertip

Nu este niciodata singular

Poate avea subtipuri ale lor

Se mai numeste subentitate

Subtipurile au mai multe atribute in comun. Aceste atributele comune sunt listate la nivelul supertipului. Acelasi lucru este valabil si pentru relatii. Subtipurile mostenesc toate atributele si relatiile supertipului entitate.

O entitate niciodata nu are un singur subtip.

Reguli:

- Exhaustive: sunt acoperite toate cazurile posibile, adica in exemplul nostru, orice publucatie este o carte (BOOK), o revista (MAGAZINE), brosura promotionala (PROMO BROCHURE), iar pt. a fi siguri ca acoperim toate situatiile sau daca ne gandim ca in viitor vom putea avea si alte produse s-a inclus si subtipul OTHER.

- Mutually Exclusive: orice instanta a unui supertip apartine doar unui singur subtip, adica un produs nu poate fi simultan atat carte cat si revista.

L2. Documentarea regulilor afacerii

STRUCTURAL RULES:

indica tipurile de informatii care urmeaza sa fie stocate si modul in care  elementele de informare interrelationeaza

care se pot deduce de pe ERD

Exemplu: 

1. Toti profesorii din scoala trebuie sa aiba o diploma de licenta. (=>campul licenta este obligatoriu!)

2. Toate comenzile de la un restaurant trebuie sa fie manipulate de catre un membru al personalului.

PROCEDURAL RULES:

sunt de flux de lucru

nu poate fi intotdeauna prinse in diagrama entitate relatie insa trebuie sa fie documentate.

Multe dintre regulile procedurale sunt legate de timp: evenimentul A trebuie sa se intample inainte de evenimentul B.

Pentru a asigura respectarea acestor reguli se apeleaza la software. Aceste reguli trebuie sa fie documentate.

Exemplu:

1. Pentru a participa la cursul de Programare elevii trebuie sa fi parcurs cursul de Algebra. (se va scrie un program care verifica in baza de date daca elevul a facut acest curs)

'Only teachers may supervise exams' is an example of which of the following?

A procedural business rule

An attribute that should be stored on the PERSON entity

A structural business rule

An attribute that is not be inherited from the PERSON supertype and is unique to the

TEACHER subtype

Why is it important to identify and document structural rules?

Ensures we know what data to store and how that data works together.

Ensures nothing. There is no benefits to be gained from documenting your Structural

Business Rules. We need to concentrate on the Procedural Business Rules only.

Ensures we know what Information to store and how that Information works together.

All of the Above.

A new system would have a mixture of both Procedural and Structural

Business Rules as part of the documentation of that new system. True or False?

True

False

A subtype can have a relationship not shared by the supertype. True or False?

True

False

Which of the following is the best scenario for using supertype/subtype entities:

A pet store that sells small animals, because they each need different size cages and food.

An ice cream store that sells ice cream in sugar cones and regular cones.

A grocery store that gives customers a choice of plastic or paper bags.

A vehicle dealership that sells cars, trucks, and boats on trailers. (*)

All instances of the subtypes must be an instance of the supertype. True or False?

True

False

All instances of the supertype are also instances of one of the subtypes. True or False?

True

False

A supertype should have at least two subtypes. True or False?

True

False

Which of the following is true about supertypes and subtypes?

Instances that belong to two subtypes of the same supertype may be modeled as a one-toone

relationship between the two subtypes.

Subtypes inherit the relationships and attributes of the supertype.

Subtypes may have no more than 2 levels of nesting.

Supertype and subtype entities must be mutually exclusive.

The 'Other' subtype is best used:

For instances that belong to the supertype and at least one other subtype.

For a subtype that does not have any of the same attributes as the supertype to which it

belongs.

As an extra subtype to ensure that all instances of subtypes are mutually exclusive and

complete. By having an 'Other' subtype, all instances of the Supertype will be of one

subtype type.

You should never have a subtype called Other.

When creating entities it is important to remember all of the following: (Choose Two)

Create a formal description.

Include attributes.

Do not use synonyms.

Do use reserved words.

Which of the following are valid formats for an attribute? (Choose Two)

Character string.

Decimal.

Number.

HEX.

How should you handle constraints that cannot be modeled on an ER diagram?

Always let the network architect handle them

List them on a separate document to be handled programmatically

Explain them to the users so they can enforce them

All constraints must be modeled and shown on the ER diagram

How would you model a business rule that states that on a student's birthday, they do not have to attend their classes?

Use a supertype

Use a subtype

Make the attribute Birthdate mandatory

You cannot model this. You need to document it

Which of the following is an example of a structural business rule?

All employees must belong to at least one department.

Buildings to be purchased by the business must be current with earthquake building code.

All overdue payments will have an added 10 % late fee.

All products will have a selling price no less than 30 % greater than wholesale.

'Only managers can approve travel requests' is an example of which of the following?

A structural business rule.

A mandatory business rule.

A procedural business rule.

An optional business rule.

A business rule such as 'All accounts must be paid in full within 10 days of billing' is best enforced

by:

Making the payment attribute mandatory.

Making the relationship between CUSTOMER and PAYMENT fully mandatory and 1:1 on both

sides.

Creating a message to be printed on every bill that reminds the customer to pay within ten

days.

Hiring a programmer to create additional programming code to identify and report accounts

past due.

Business rules are important to data modelers because:

A. They capture all of the needs, processes, and required functionality of the business.

B. They are easily implemented in the ERD diagram.

C. The data modeler must focus on structural rules, because they are easily represented

diagrammatically, and eliminate other rules that involve extra procedures or programming.

D. Both A and C are true

Why is it important to identify and document business rules?

It allows you to create your data model, then check for accuracy.

It allows you to improve the client's business.

It ensures that the data model will automate manual processes.

None of the above.