CS 5150
Software Engineering
Lecture 15
Program Design 2
Administrivia
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TAs reading milestone 2 reports
Everyone do teammate feedback?
Quiz 2
No final exam
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General Presentation Feedback
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Client single point of contact
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SE in the News
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Google releases Dart SDK
Largest Kickstarter project funded -$4M
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Microsoft app store craziness
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Zero-day exploit lifecycle analysis
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Conditions on MSFT’s App Store
5.2 Your app must not contain content that advocates discrimination,
hatred, or violence based on membership in a particular racial, ethnic,
national, linguistic, religious, or other social group, or based on a person’s
gender, age, or sexual orientation5.3 Your app must not contain content or
functionality that encourages, facilitates or glamorizes illegal activity5.4
Your app must not contain or display content that a reasonable person
would consider to be obscene5.5 Your app must not contain content that
is defamatory, libelous or slanderous, or threatening5.6 Your app must not
contain content that encourages, facilitates or glamorizes excessive or
irresponsible use of alcohol or tobacco products, drugs or weapons5.7
Your app must not contain content that encourages, facilitates or
glamorizes extreme or gratuitous violence, human rights violations, or the
creation or use of weapons against a person or animal in the real world5.8
Your app must not contain excessive or gratuitous profanity
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Attack Timeline
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Quiz 2
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Requirements
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Scenarios/use cases
Diagrams: dataflow, flow chart, entity
relation, sequence
Usability
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Interface/user testing
Software architecture
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Design patterns
Concurrency
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Program Design
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The task of program design is to represent the software
system functions in a form that can be transformed into
one or more executable programs
Given a system architecture, the program design
specifies:
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programs, components, packages, classes and class
hierarchies
interfaces, protocols (where not part of the system
architecture)
algorithms, data structures, security mechanisms,
operational procedures
If the program design is done properly, all design
decisions should be made before implementation
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UML Models
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UML models (diagrams and specifications)
can be used for almost all aspects of program
design
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Diagram gives a general overview of the
model, showing the principal elements and
how they relate to each other.
Specification provides details about each
element of the model. Specification for
models used in program design should have
sufficient detail that they can be used to
write code from.
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Class Diagrams
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Class Diagram in Rational Rose
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Notation: Relationships
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Like Database Schema
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Notation: Relationships (continued)
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Notation: Interface
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Notation: Package
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Modeling Classes
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Given a real-life system, how do you decide
what classes to use?
What terms do the users and implementers use
to describe the system? They are candidates
for classes.
Is each candidate class crisply defined?
For each class, what is its set of
responsibilities? Are the responsibilities evenly
balanced among the classes?
What attributes and operations does each class
need to carry out its responsibilities?
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Candidate Classes:
Application Classes and Solution Classes
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Application classes represent application
concepts.
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Noun identification is an effective technique
to generate candidate application classes
Solution classes represent system concepts,
e.g., user interface objects, databases, etc.
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From Candidate Classes to Completed
Design
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Methods used to move to final design:
Reuse: Wherever possible use existing
components, or class libraries. They may need
modification.
Restructuring: Change the design to improve,
understandability, maintainability, etc.
Techniques include merging similar classes,
splitting complex classes, etc.
Optimization: Ensure that the system meets
anticipated performance requirements, e.g., by
changed algorithms or restructuring.
Completion: Fill all gaps, specify interfaces, etc.
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Coupling and Cohesion
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Coupling is a measure of the dependencies
between two part of a system. If two classes
are strongly coupled, it is hard to modify one
without modifying the other.
Cohesion is a measure of dependencies within
part of a system. If a class contains many
closely related functions its cohesion is high.
Aim for high cohesion within classes and weak
coupling between them.
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