1. Database Design Dr. M.E. Fayad, Professor
5/18/2019
Database Design
Dr. M.E. Fayad, Professor
Computer Engineering Department, Room #283I
College of Engineering
San José State University
One Washington Square
San José, CA
© Dr. M.E. Fayad
SJSU -- CmpE

2. Lesson 2: Data Modeling Using Entity-Relationship Model
5/18/2019
Lesson 2:
Data Modeling Using
Entity-Relationship
Model 2
© Dr. M.E. Fayad
SJSU – CmpE --- M.E. Fayad

3. 3 Lesson Objectives Understand the notation of ERDs
5/18/2019
Lesson Objectives
Understand the notation of ERDs
Learn how to do ER Analysis
Illustrate examples for ERDs 3
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SJSU – CmpE --- M.E. Fayad

4. What Is Entity-Relationship Diagrams?
5/18/2019
What Is Entity-Relationship Diagrams?
E-R diagrams (ERDs):
Identify major ingredients, entities, of a complicated situation
Identify characteristics, attributes, of the major ingredients
Uncover and analyze interconnections, relationships, among the major ingredients
Assess various aspects of the relationships 4
© Dr. M.E. Fayad
SJSU – CmpE --- M.E. Fayad

5. What Is Entity-Relationship Diagrams?
5/18/2019
What Is Entity-Relationship Diagrams?
ERD – Chen 1976
Precursor to the class diagram – Will be covered later.
No generalization
ERD
Entities: Information holding structures
Relationships: Connections between entities
Cardinalities: Upper bounds
Modalities: Lower bounds
Attributes: Properties, characteristics, … associated with an entity. 5
© Dr. M.E. Fayad
SJSU – CmpE --- M.E. Fayad

6. What Is Entity-Relationship Diagrams?
5/18/2019
What Is Entity-Relationship Diagrams?
In short, ERD strives
to take a close look at the ingredients of a puzzle
in order to identify major and minor ingredients
and to figure out how they relate to each other 6
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SJSU – CmpE --- M.E. Fayad

7. Entity-Relationship Diagrams
5/18/2019
Entity-Relationship Diagrams
ERD can be summarized as the process of uncovering, analyzing, and explicating (i.e., stating clearly and fully) the business rules governing a complicated situation 7
© Dr. M.E. Fayad
SJSU – CmpE --- M.E. Fayad

8. 5/18/2019
Business Rules (1)
Business rules are precise statements, derived from a detailed description of the organization's operations, that define one or more of the following modeling components:
Entities
Relationships
Attributes
Connectivities
Cardinalities
Constraints
1Rob, P.; Coronel, C. Instructor’s Manual to Accompany Database Systems: Design, Implementation, and Management. Fourth Edition. CD-ROM 8
© Dr. M.E. Fayad
SJSU – CmpE --- M.E. Fayad

9. 9 Business Rules (2) Examples of business rules1
5/18/2019
Business Rules (2)
Examples of business rules1
An invoice contains one or more invoice lines, but each invoice line is associated with a single invoice. That is,
An invoice contains one or more invoice lines.
Each invoice line is associated with a single invoice.
A store employs many employees, but each employee is employed by only one store.
A college has many departments, but each department belongs to a single college. (This business rule reflects a university that has multiple colleges such as Business, Liberal Arts, Education, Engineering, etc.)
1From: Rob, P.; Coronel, C. Instructor’s Manual to Accompany Database Systems: Design, Implementation, and Management. Fourth Edition. CD-ROM 9
© Dr. M.E. Fayad
SJSU – CmpE --- M.E. Fayad

10. 10 Business Rules (3) Examples of business rules1
5/18/2019
Business Rules (3)
Examples of business rules1
A driver may be assigned to drive many different vehicles, and each vehicle can be driven by many drivers. (Note: Keep in mind that this business rule reflects the assignment of drivers over a period of time.)
A client may sign many contracts, but each contract is signed by only one client.
A sales representative may write many contracts, but each contract is written by one sales representative 10
© Dr. M.E. Fayad
SJSU – CmpE --- M.E. Fayad

11. 11 Business Rules (4) Some business rules for a library
5/18/2019
Business Rules (4)
Some business rules for a library
Books and other materials exist in various editions and numbers of copies
Books may or may not circulate
Books that circulate may do so for varying periods
Periods may be determined by
Book status alone
Borrower status alone
Combination of book status and borrower status 11
© Dr. M.E. Fayad
SJSU – CmpE --- M.E. Fayad

12. 12 Business Rules (5) More business rules for a library
5/18/2019
Business Rules (5)
More business rules for a library
Users may have various statuses
Users may have varying numbers of items currently charged out to them
Users may or may not owe fines
Fine status may or may not affect eligibility to borrow 12
© Dr. M.E. Fayad
SJSU – CmpE --- M.E. Fayad

13. 13 Business Rules (6) More business rules for a library
5/18/2019
Business Rules (6)
More business rules for a library
Staff members have attributes of
Salary or wage rates
Annual leave
Sick leave
Work schedules
Job titles
Special skills (e.g., languages, puppetry)
Hire dates
Total length of service
Professional organization memberships 13
© Dr. M.E. Fayad
SJSU – CmpE --- M.E. Fayad

14. 14 Business Rules (7) More business rules for a library
5/18/2019
Business Rules (7)
More business rules for a library
Physical facilities include
Branches
Furniture
Machines (e.g., computers, microform readers, automobiles, players for CD-ROMs, audiotapes, videotapes)
Library-management software
Catalog records (e.g., computerized databases, catalog cards)
Records of inventory, acquisitions, circulation, personnel 14
© Dr. M.E. Fayad
SJSU – CmpE --- M.E. Fayad

15. 15 Business Rules (8) More business rules for a library
5/18/2019
Business Rules (8)
More business rules for a library
Related organizations may include
City, university, or corporate administrations
Employee unions
Friends of the Library organizations
Vendors of books, serials, and other products and services used by the library
Networks of which the library is a member (e.g., OCLC, Amigos, Association of Research Libraries, Texas State Library network, Central Texas Library System) 15
© Dr. M.E. Fayad
SJSU – CmpE --- M.E. Fayad

16. 5/18/2019
E-R Diagrams (1)
E-R analysis relies heavily on diagrams to represent
Entities (rectangles)
Attributes (ellipses)
Relationships (diamonds)
Connections (lines, which may have arrowheads or crowsfeet to represent degrees of connectivity or relationship) 16
© Dr. M.E. Fayad
SJSU – CmpE --- M.E. Fayad

17. Entity Relationship Diagrams
5/18/2019
Entity Relationship Diagrams
Data models are tools used in analysis to describe the data requirements and assumptions in the system from a top-down perspective. There are three basic elements in ER models:
Entities are the "things" about which we seek information.
Attributes are the data we collect about the entities.
Relationships provide the structure needed to draw information from multiple entities. 17
© Dr. M.E. Fayad
SJSU – CmpE --- M.E. Fayad

18. 5/18/2019
Developing ERDs
Developing an ERD requires an understanding of the system and its components. Before discussing the procedure, let's look at a narrative created by Professor Harman.
Consider a hospital: Patients are treated in a single ward by the doctors assigned to them. Usually each patient will be assigned a single doctor, but in rare cases they will have two.
Heathcare assistants also attend to the patients, a number of these are associated with each ward. 18
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SJSU – CmpE --- M.E. Fayad

19. 5/18/2019
Developing ERDs
Initially the system will be concerned solely with drug treatment. Each patient is required to take a variety of drugs a certain number of times per day and for varying lengths of time.
The system must record details concerning patient treatment and staff payment. Some staff are paid part time and doctors and care assistants work varying amounts of overtime at varying rates (subject to grade).
The system will also need to track what treatments are required for which patients and when and it should be capable of calculating the cost of treatment per week for each patient (though it is currently unclear to what use this information will be put). 19
© Dr. M.E. Fayad
SJSU – CmpE --- M.E. Fayad

20. 5/18/2019
How do we start an ERD? (1)
1. Define Entities: these are usually nouns used in descriptions of the system, in the discussion of business rules, or in documentation; identified in the narrative (see highlighted items above).
2. Define Relationships: these are usually verbs used in descriptions of the system or in discussion of the business rules (entity ______ entity); identified in the narrative (see highlighted items above).
3. Add attributes to the relations; these are determined by the queries,and may also suggest new entities, e.g. grade; or they may suggest the need for keys or identifiers. 20
© Dr. M.E. Fayad
SJSU – CmpE --- M.E. Fayad

21. 21 How do we start an ERD? (2) What questions can we ask?
5/18/2019
How do we start an ERD? (2)
What questions can we ask?
a. Which doctors work in which wards?
b. How much will be spent in a ward in a given week?
c. How much will a patient cost to treat?
d. How much does a doctor cost per week?
e. Which assistants can a patient expect to see?
f. Which drugs are being used? 21
© Dr. M.E. Fayad
SJSU – CmpE --- M.E. Fayad

22. 5/18/2019
How do we start an ERD? (3)
4. Add cardinality to the relations Many-to-Many must be resolved to two one-to-manys with an additional entity
Usually automatically happens
Sometimes involves introduction of a link entity (which will be all foreign key) Examples: Patient-Drug
5. This flexibility allows us to consider a variety of questions such as: a. Which beds are free?
b. Which assistants work for Dr. X?
c. What is the least expensive prescription?
d. How many doctors are there in the hospital?
e. Which patients are family related?
6. Represent that information with symbols. 22
© Dr. M.E. Fayad
SJSU – CmpE --- M.E. Fayad

23. 23 ERDs Overview Concepts Rules Guidelines
5/18/2019
ERDs
Overview
Concepts
Rules
Guidelines
<See Documents with Lecture 04> 23
© Dr. M.E. Fayad
SJSU – CmpE --- M.E. Fayad

24. Crucial Use of E-R Analysis (1)
5/18/2019
Crucial Use of E-R Analysis (1)
It is especially important to identify and note many-to-many (M:N) relationships: for example1
Note: The small circle denotes optionality (a person need not be a customer; but to be a customer, he or she must rent at least one tape) 24
1From: Rob, P.; Coronel, C. Instructor’s Manual to Accompany Database Systems:
Design, Implementation, and Management. Fourth Edition. CD-ROM
© Dr. M.E. Fayad
SJSU – CmpE --- M.E. Fayad

25. Crucial Use of E-R Analysis (2)
5/18/2019
Crucial Use of E-R Analysis (2)
The typical resolution of many-to-many (M:N) relationships is by a bridge table (also called a composite entity) 25
© Dr. M.E. Fayad
SJSU – CmpE --- M.E. Fayad

26. Crucial Use of E-R Analysis (3)
5/18/2019
Crucial Use of E-R Analysis (3)
A further explication of the resolution of the M:N relationship 26
© Dr. M.E. Fayad
SJSU – CmpE --- M.E. Fayad

27. 27 Discussion Questions T/F ERD supports generalization.
5/18/2019
Discussion Questions
T/F
ERD supports generalization.
Cardinality of one is symbolized by a bar -- | --written across the relationship line.
An entity type must have at least one relevant attribute type.
Entity Type Name is Synonyms and Homonyms.
Cardinality: A business rule indicating the number of times a particular object or activity may occur. 27
© Dr. M.E. Fayad
SJSU – CmpE --- M.E. Fayad

28. 5/18/2019
Tasks for Next Lecture
Task 1: Team forming – Team name, Team members’ names (2-3) per team, and team members’ s
Task 2: Contact information – your name, , and phone #
Task 3: Practical exercise: ERDs
Task 4: Assignment #1 28
© Dr. M.E. Fayad
SJSU – CmpE --- M.E. Fayad