Database Design Sections 4 & 5 Subtype, Supertype, Mutually exclusive, non-transferability, transferable, 1:1, 1:M, M:M, Redundant, Intersection entity, Barred relationship, First Normal Form (1NF)

DJs on Demand – Partial ERD

Reserved Words  A reserved work is one that has a specific meaning and function in the computer system, language, or database.  Examples: NULL DATE DISTINCT

Video Store – example  Identify business rules  Construct ERD  Class activity

Video Store Matrix ACTORCUSTO- MER MOVIETAPE ACTOR Featured in CUSTO- MER The renter of MOVIE The feature of On TAPE Rented byA copy of

Video ERD featured in TAPE number format MOVIE id title category ACTOR stage name real name CUSTOMER membership number last name first name phone number a copy of on the feature of rented by the renter of

Use Source Documents  Source document assist in identifying entities, attributes, and relationships

Global Fast Food  Identify entities

Possible solution ORDER #number *date *time STAFF #id *first name *last name *date of birth *salary FOOD ITEM #number *description *price handle handled by list listed on

Subtype & Supertype  Supertype (entity) can be subdivided into Subtypes  Example: JOB manager clerk sales support

Attributes  Supertype can have attributes at supertype level  Attributes at supertype level are for all subtypes  Subtypes can have own attributes for only that attribute

Example EXAM #number *description *weight *date *grade for written component MIDTERM * grade for oral presentation FINAL *extra pts for opt. paper QUIZ BONUS QUESTIONS STUDENT included in included taken by

Global Fast Food Employees  STAFF is an entity and supertype  What are the attributes of STAFF?  What subtypes exist in STAFF? Are there any attributes in any of the subtypes?

Example  AUTOMOBILE subtypes are not mutually exclusive  AUTOMOBILE possible solution  BUILDING subtypes have problem of not being exhaustive, should be minimum of 2 types

Business Rules  Recognize if Business rule is implemented by the data model or by programming  Example: Only an employee with a title of manager can manage other employees The event planner must contact the customer before the DJ can be assigned  Business rules can changed as society changes or business leaders feel change needed

Business rule types  Structural Must be entered at time of initial data entry  Example: When ORDER entered a staff id must be entered  Does not require code written to enforce  Procedural Work flow related Programmed validation is procedural constraint  Generally need to write code  Example: Commission can not be > 25% of salary

Each entity has  Name  Optionality  Cardinality  Transferability

Relationship transferability  Rules established for the purpose such as safety, efficiency, or increased profit  Example: Airline tickets can be transferable or non-transferable?  Non-transferable means also not updatable  symbol used to denote non- transferable blood type is non-transferable

Non-transferable relationship  Orders are non-transferable  Resolution would be to cancel order and create new order CUSTOMER ORDER place placed by

Example #1  Each town may be the birthplace of many people. Each person must be born in one and only one town. PEOPLE TOWN birthplace for born in

Relationship types  One to One (1:1)  One to Many (1:M)  Many to Many (M:M)

One to One relationship  Usually few of these relationships  Often mandatory at one side  If mandatory at both ends be aware, it might be a error. Possible should be only one entity not two PERSON BYCYCLE ride ridden by

One to Many  Most common type are mandatory on one side and optional on the other  Mandatory at both ends models entities that cannot exist without each other ORDER ORDER TYPE

One to Many example TAX RETURN TAX REPORT LINE BANDMUSICIAN composed of belong to composed of entered in

Many to Many  Often common in initial version of ERD  Later stage of design converted to other type STUDENT TEACHER learn from educate

Redundant relationship  Redundant relationship is one that can be derived from another relationship in the model

Many to Many Relationship Resolution  All M:M relationships must be changed to a set of 1:M and M:1 relationship  Insert a transition entity between  Occurs when you go from conceptual model to design model

Example: M:M with Intersection Entity STUDENT COURSE REGISTRATION

Resolving M:M with Intersection  Create an intersection entity  If you can’t find a good intersection entity create one by concatenate two entities together

Example PARTNER EVENT WORK ASSIGNMENT (PARTNER_EVENT)

Normalization  To make sure you don’t store the same data twice in the model  Also, that you store the data in the correct place  We will cover the first 3 normal forms.

First Normal Form (1NF)  First Normal Form requires that there be no multivalued attributes and no repeating groups.  To check for 1NF, validate that each attribute has a single value for each instance of the entity.  In other words: “One value per Attribute”.

Example 1NF  This has multiple values for the classroom. SCHOOL BUILDING #code *name *address *classroom

Example 1NF  Telephone is a multvalued attribute that could be an Entity. Ie. Home, work, mobile, fax etc.  Not all Employees have multiple phones, so there would eliminate multiple NULL values. EMPLOYEE #id *name *address. º telephone º salary

Review 1NF examples  Look at the 4 examples on 5.4.4