COSC 4406 Software Engineering

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COSC 4406Software Engineering
Haibin Zhu, Ph.D. Dept. of Computer Science and
mathematics, Nipissing University, 100 College
Dr., North Bay, ON P1B 8L7, Canada,
haibinz_at_nipissingu.ca, http//www.nipissingu.ca/fa
culty/haibinz
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Lecture 9 Component-Level Designand User
Interface Design
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What is a Component?

• OMG Unified Modeling Language Specification
  OMG01 defines a component as
• a modular, deployable, and replaceable part of
  a system that encapsulates implementation and
  exposes a set of interfaces.
• OO view a component contains a set of
  collaborating classes
• Conventional view logic, the internal data
  structures that are required to implement the
  processing logic, and an interface that enables
  the component to be invoked and data to be passed
  to it.

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OO Component
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Conventional Component
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Designing Class-Based Components
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Basic Design Principles

• The Open-Closed Principle (OCP). A module
  component should be open for extension but
  closed for modification.
• The Liskov Substitution Principle (LSP).
  Subclasses should be substitutable for their
  base classes.
• Dependency Inversion Principle (DIP). Depend on
  abstractions. Do not depend on concretions.
• The Interface Segregation Principle (ISP). Many
  client-specific interfaces are better than one
  general purpose interface.
• The Release Reuse Equivalency Principle (REP).
  The granule of reuse is the granule of release.
  
• The Common Closure Principle (CCP). Classes that
  change together belong together.
• The Common Reuse Principle (CRP). Classes that
  arent reused together should not be grouped
  together.

Source Martin, R., Design Principles and
Design Patterns, downloaded from
http//www.objectmentor.com, 2000.
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Design Guidelines

• Components
• Naming conventions should be established for
  components that are specified as part of the
  architectural model and then refined and
  elaborated as part of the component-level model
• Interfaces
• Interfaces provide important information about
  communication and collaboration (as well as
  helping us to achieve the OPC)
• Dependencies and Inheritance
• it is a good idea to model dependencies from left
  to right and inheritance from bottom (derived
  classes) to top (base classes).

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Cohesion

• Conventional view
• the single-mindedness of a module
• OO view
• cohesion implies that a component or class
  encapsulates only attributes and operations that
  are closely related to one another and to the
  class or component itself
• Levels of cohesion
• Functional only one function
• Layer one direction dependence
• Communicational shared data
• Sequential pipeline (ones out is the followers
  in)
• Procedural invoked one by one
• Temporal special behaviors such as exception
  handling
• Utility similar components/classes/operations
  grouped together

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Coupling

• Conventional view
• The degree to which a component is connected to
  other components and to the external world
• OO view
• a qualitative measure of the degree to which
  classes are connected to one another
• Level of coupling
• Content access others internal data
• Common share global data
• Control A() calls B() by passing a control flag.
• Stamp classB is declared as a type for an
  argument of an operation of classA
• Data when passing large data
• Routine call one invokes another
• Type use one component A uses the types of
  another component B
• Inclusion or import component A imports
  component B
• External a component communicates with
  components of another component

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Component Level Design-I

• Step 1. Identify all design classes that
  correspond to the problem domain.
• Step 2. Identify all design classes that
  correspond to the infrastructure domain.
• Step 3. Elaborate all design classes that are
  not acquired as reusable components.
• Step 3a. Specify message details when classes or
  component collaborate. (UML collaboration
  diagram)
• Step 3b. Identify appropriate interfaces for
  each component.
• Step 3c. Elaborate attributes and define data
  types and data structures required to implement
  them.
• Step 3d. Describe processing flow within each
  operation in detail. (UML activity diagram)

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Component-Level Design-II

• Step 4. Describe persistent data sources
  (databases and files) and identify the classes
  required to manage them.
• Step 5. Develop and elaborate behavioral
  representations for a class or component. (UML
  statechart)
• Step 6. Elaborate deployment diagrams to provide
  additional implementation detail.
• Step 7. Factor every component-level design
  representation and always consider alternatives.

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Collaboration Diagram
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Refactoring
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Activity Diagram
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Statechart
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Algorithm Design

• the closest design activity to coding
• the approach
• review the design description for the component
• use stepwise refinement to develop algorithm
• use structured programming to implement
  procedural logic
• use formal methods to prove logic

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Stepwise Refinement
open
walk to door
reach for knob

open door
repeat until door opens

turn knob clockwise
walk through
if knob doesn't turn, then
close door.
take key out
find correct key
insert in lock
endif
pull/push door move out of way
end repeat
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Algorithm Design Model

• represents the algorithm at a level of detail
  that can be reviewed for quality
• options
• graphical (e.g. flowchart, box diagram)
• pseudocode (e.g., PDL) ... choice of many
• programming language
• decision table
• conduct walkthrough to assess quality

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Structured Programmingfor Procedural Design
uses a limited set of logical constructs

sequence


conditional
if-then-else, select-case

loops
do-while, repeat until

leads to more readable, testable code

can be used in conjunction with proof of
correctness
important for achieving high quality, but not
enough
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A Structured Procedural Design
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Decision Table
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Program Design Language (PDL)
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Interface Design
Easy to learn?
Easy to use?
Easy to understand?
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Interface Design
Typical Design Errors
lack of consistency too much memorization no
guidance / help no context sensitivity poor
response Arcane/unfriendly
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Golden Rules

• Place the user in control
• Reduce the users memory load
• Make the interface consistent

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Place the User in Control

• Define interaction modes in a way that does not
  force a user into unnecessary or undesired
  actions.
• Provide for flexible interaction.
• Allow user interaction to be interruptible and
  undoable.
• Streamline interaction as skill levels advance
  and allow the interaction to be customized.
• Hide technical internals from the casual user.
• Design for direct interaction with objects that
  appear on the screen.

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Reduce the Users Memory Load

• Reduce demand on short-term memory.
• Establish meaningful defaults.
• Define shortcuts that are intuitive.
• The visual layout of the interface should be
  based on a real world metaphor.
• Disclose information in a progressive fashion.

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Make the Interface Consistent

• Allow the user to put the current task into a
  meaningful context.
• Maintain consistency across a family of
  applications.
• If past interactive models have created user
  expectations, do not make changes unless there is
  a compelling reason to do so.

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User Interface Design Models

• User model a profile of all end users of the
  system
• Design model a design realization of the user
  model
• Mental model (system perception) the users
  mental image of what the interface is
• Implementation model the interface look and
  feel coupled with supporting information that
  describe interface syntax and semantics

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User Interface Design Process
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Interface Analysis

• Interface analysis means understanding
• (1) the people (end-users) who will interact with
  the system through the interface
• (2) the tasks that end-users must perform to do
  their work,
• (3) the content that is presented as part of the
  interface
• (4) the environment in which these tasks will be
  conducted.

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User Analysis

• Are users trained professionals, technician,
  clerical, or manufacturing workers?
• What level of formal education does the average
  user have?
• Are the users capable of learning from written
  materials or have they expressed a desire for
  classroom training?
• Are users expert typists or keyboard phobic?
• What is the age range of the user community?
• Will the users be represented predominately by
  one gender?
• How are users compensated for the work they
  perform?
• Do users work normal office hours or do they work
  until the job is done?
• Is the software to be an integral part of the
  work users do or will it be used only
  occasionally?
• What is the primary spoken language among users?
• What are the consequences if a user makes a
  mistake using the system?
• Are users experts in the subject matter that is
  addressed by the system?
• Do users want to know about the technology the
  sits behind the interface?

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Task Analysis and Modeling

• Answers the following questions
• What work will the user perform in specific
  circumstances?
• What tasks and subtasks will be performed as the
  user does the work?
• What specific problem domain objects will the
  user manipulate as work is performed?
• What is the sequence of work tasksthe workflow?
• What is the hierarchy of tasks?
• Use-cases define basic interaction
• Task elaboration refines interactive tasks
• Object elaboration identifies interface objects
  (classes)
• Workflow analysis defines how a work process is
  completed when several people (and roles) are
  involved

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Swimlane Diagram
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Analysis of Display Content

• Are different types of data assigned to
  consistent geographic locations on the screen
  (e.g., photos always appear in the upper right
  hand corner)?
• Can the user customize the screen location for
  content?
• Is proper on-screen identification assigned to
  all content?
• If a large report is to be presented, how should
  it be partitioned for ease of understanding?
• Will mechanisms be available for moving directly
  to summary information for large collections of
  data.
• Will graphical output be scaled to fit within the
  bounds of the display device that is used?
• How will color to be used to enhance
  understanding?
• How will error messages and warning be presented
  to the user?

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Interface Design Steps

• Using information developed during interface
  analysis (SEPA, Section 12.3), define interface
  objects and actions (operations).
• Define events (user actions) that will cause the
  state of the user interface to change. Model this
  behavior.
• Depict each interface state as it will actually
  look to the end-user.
• Indicate how the user interprets the state of the
  system from information provided through the
  interface.

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Interface Design Patterns

• Patterns are available for
• The complete UI
• Page layout
• Forms and input
• Tables
• Direct data manipulation
• Navigation
• Searching
• Page elements
• e-Commerce

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Design Issues

• Response time
• Help facilities
• Error handling
• Menu and command labeling
• Application accessibility
• Internationalization

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Design Evaluation Cycle
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Summary

• Component-Level Design
• Component
• Class-based Components
• Conducting Component-level Design
• Designing Conventional Components
• Interface Design
• Golden Rules
• UI Analysis
• UI Design
• UI Design Evaluation