1. Some Simple Design Modeling Techniques
State Transition Diagram to model the functional and execution (dynamic) aspects of the software system
Entity-Relation Diagram to model the data, data attributes and data relationships
UML’s Sequence Diagram to model object interactions.

2. State Transition Diagram for Detail Design
State Transition Diagrams were heavily used in
compiler design (strings that are acceptable)
automata theory (machine states)
State Transition diagram depicts a machine (system) composed of a (1) set of states, S, and (2)a set of alphabet (inputs) or stimulants, I, an (3) initial and (4) a final state and (5) a set of transition rules, R such that the following depicts the state transitions
r (s1, a) = s where
s1, s2 are members of S (states) and
a is a member of I
r is a transition rule in R

3. Simple State Transition Design1 S1 So 1
- Define the initial and final states to be the same S0.
- The transition rules are:
r1: (S0, 0) = S1
r2: (S0, 1) = S0
r3: (S1, 0) = S1
r4: (S1, 1) = S0
A system that will accept all strings of 0’s and 1’s that end with 1

4. Self-Exercise
Use State Transition diagram to depict a system that will accept strings made of 0’s and 1’s, but only those that have an even number of 0’s and 1’s.

5. One Answer S1 So 1 1 1 1 S3 S2

6. A More Design Oriented Representation of A Process Flow
Search again
Display all
flights
Display all
airlines with
available seat
Start
‘Available’
Flight Search
Check seat
availability
Search flights to
destination x by
date
Terminate
search
Terminate
Flight Search
function
Note that this is a search only for flights with
available seats, not a general flight search

7. Using State Transition Diagram for Design
Good for modeling the “states” and “transitions of states” of a system, of a component of a system, or a small segment of a component.
In order to use this modeling technique one has to think of:
All possible states: S’s
All possible stimuli for change of state: I’s
All the possible rules for transitions of states: R ( Ik,Si) -> Sj
Initial or starting state of the system: S0
Terminating state
may be used as a tool to “test” out the component: e.g error path

8. Entity Relationship Diagram (ERD)
ERD was introduced as a technique to model Data Conceptual Model about 20 years ago, before introduction of OO, when it was realized that both data and functionality need to be considered together.
Description of Data Types:
Relationship among Data
Constraints on Relationship
From the ERD diagram, the Next step is Logical Database Design where ERD is mapped into Database Schema.
Besides DB, ERD May be used with OO techniques in designing Classes

9. Entity and Attributes Entity is a “thing” which may be of :
Physical Existence such as cars, employees, lumber, etc.
Conceptual Existence such as company, project, payroll, etc.
Attribute is a property that describes the Entity (such as an employee may have attributes of sex, age, address, etc.).
An attribute may be :
Simple or Composite : gender is simple where address is a composite
Single or Multi Valued: gender is single valued where car-color may be multi-valued (e.g. green-and-white is multi-color)
Stored or Derived: birth-date is stored where age may be derived (from today’s date minus birth-date)
Null : not applicable or unknown as opposed to blank
Also, an interesting design question.

10. Example of Entity and Attributes
- An Entity is represented as
a rectangular box
Employee
- Attributes are represented as
a) ovals attached to the entity or
b) listed within the entity box
(b)
(a)
Employee
Employee
-Name
-Sex
-Address
- Street
- City
- State
- Zip
Name
Address
Sex
Street
City
State
Zip

11. Further Descriptions of Entities and Attributes
Entity Type represents a set of entities that have the same attributes.
Note the similarity between Entity Type and Class and each entity and each object
Entity Type is
“Employee”
- employee1(Joe, male, 43)
- employee2(Tom,male, 32) .
“Key” Attribute is an attribute which has a unique value and
may be used as search index, and is represented with an underline.
Employee
Name
Employee
Number
Address

12. Entity Relationships
A Relationship, R, is an association between or among Entity Types.
Employee R Project
where R may be defined as “work on”
Degree of Relationship defines the number of participating entity types for that relationship.
Binary : Employee “works for” Customer
Ternary : Equipment “supplies” Project and Employee “supplies” Project
Works for
Customer
Employee
Equipment
Supplies
Project
Supplies
Employee

13. Constraints on Relationship
Constraints are “limitations” put on the entities that participate in a relationship:
Cardinality
Modality
Cardinality: specifies the number of occurrences of one entity that can be related to the number of occurrences of another entity:
one-to-one : ( person to seat) where each person occupies a seat and each seat is occupied by one person
one-to-many : (artist to paintings) where each artist can paint many paintings but each painting is painted by one artist
man-to-many : (students to classes) where many students are enrolled in a class and a student may be enrolled in many classes

14. Constraints on Relationship (cont.)
Modality (or participation or existence) specifies whether the existence of an entity depends on its being related to another entity via the relationship:
Total : Every entity of the entity type participates in the relationship
Partial : Some of the entities of the entity type may participate in the relationship
Author
write
Book
act
Stage play
Actor
Author, Actor (Partial) - because not all authors have written a book or
actors played on stage
Book, stage play (Total)- because every book is written by an author or every
stage play is acted by actors

15. Cardinality and Modality Representation1 m
Writes
Author
Book
Cardinality of 1 ( author) to (writes) many (books)
Author
Book
(mandatory)
(optional)
Modality specifying that an author is mandatory for each book, but
book is optional for author because some author never wrote a book

16. Represent Performance Requirement and Design (using UML Sequence Diagram as an example)
Object 1
Object 2
Object 3
Invokes an object 2
method
Invokes an object 3
method A
(B-A)<2sec.
Return B
This is the performance specification of 2 secs.
in the detail design to satisfy some requirement