Lecture 07: Conceptual Database Design
Lecture 07: Conceptual Database Design
Jan 29, 2016
Lecture 07: Conceptual Database Design. Building an Application with a DBMS. Requirements modeling (conceptual) Decide what entities should be part of the application and how they should be linked. Schema design and implementation Decide on a set of tables, attributes. - PowerPoint PPT Presentation
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Lecture 07: Conceptual Database Design
Building an Application with a DBMS
1. Requirements modeling (conceptual)– Decide what entities should be part of the application and
how they should be linked.
2. Schema design and implementation– Decide on a set of tables, attributes.– Define the tables in the database system.– Populate database (insert tuples).
3. Write application programs using the DBMS– Way easier now that the data management is taken care of.
Database Design
• Why do we need it?– Agree on structure of the database before
deciding on a particular implementation.• Consider issues such as:
– What entities to model– How entities are related– What constraints exist in the domain– How to achieve good designs
Database Design Formalisms1. Object Definition Language (ODL):
– Closer in spirit to object-oriented models– Not in the scope of this course
2. Entity/Relationship model (E/R):– More relational in nature.– Related to the EER modeling in the MySQL workbench
but we use different conventions here!
• Both can be translated to relational schemas
Entity / Relationship Diagrams
Entity sets
Attributes
Relationships between entities
Product
address
buys
Keys in E/R Diagrams
• Every entity set must have a key
Product
name category
price
buys
makes
employs
Company
name category stockprice name
price
address name ssn
Person
Product
What is a Relation ?
• A mathematical definition:– if A, B are sets, then a relation R is a subset of
A B• A={1,2,3}, B={a,b,c,d},
R = {1,a, 1,c, 3,b}
- makes is a subset of Product Company:
1
2
3
a
b
c
d
A= =B
makes CompanyProduct
Multiplicity of E/R Relations
• one-one:
• many-one
• many-many
123
abcd
123
abcd
123
abcd
buys
makes
employs
Company
name category stockprice name
price
address name ssn
Person
Product
What doesit mean?
Multi-way RelationshipsHow do we model a purchase relationship between buyers,products and stores?
Purchase
Product
Person
Can still model as a mathematical set (how?)
Store
Q: what does the arrow mean ?
A: if I know the movie, role and actor, I know the salary too
Plays
Movie
Actor
Salary
Role
Arrows in Multiway Relationships
Q: what do these arrow mean ?
A: store, person, invoice determines movie and store, invoice, movie determines person
Rental
VideoStore
Person
Movie
Invoice
Arrows in Multiway Relationships
Q: how do I say: “invoice determines store” ?
A: no good way; best approximation:
Q: Why is this incomplete ?
Rental
VideoStore
Person
Movie
Invoice
Arrows in Multiway Relationships
Roles in Relationships
Purchase
What if we need an entity set twice in one relationship?
Product
Person
Store
seller buyer
Attributes on Relationships
Purchase
Product
Person
Store
date
Converting Multi-way Relationships to Binary
Purchase
Person
Store
Product
StoreOf
ProductOf
BuyerOf
date
From E/R Diagramsto Relational Schema
• Entity relation• Relationship relation
Entity Set to Relation
Product
name category
price
Product(name, category, price)
name category price
gizmo gadgets $19.99
Relationships to Relations
Makes(product-name, product-category, company-name, year) Product-name Product-Category Company-name Starting-year
gizmo gadgets gizmoWorks 1963
(watch out for attribute name conflicts)
makes CompanyProduct
name category
Stock price
nameStart Year
price
Relationships to Relations
No need for Makes. Modify Product:
name category price StartYear companyName
gizmo gadgets 19.99 1963 gizmoWorks
makes CompanyProduct
name category
Stock price
nameStart Year
price
Multi-way Relationships to Relations
Purchase
Product
Person
Storename price
ssn name
name address
Purchase( , , )
3. Design Principles
PurchaseProduct Person
What’s wrong?
President PersonCountry
Design Principles:What’s Wrong?
Purchase
Product
Store
date
personNamepersonAddr
Moral: pick the right kind of entities.
Design Principles:What’s Wrong?
Purchase
Product
Person
Store
dateDates
Moral: don’t complicate life more than it already is.
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