Title: CSSE 501 ObjectOriented Development
1CSSE 501 Object-Oriented Development
2Today
- Chapter 3 Object-Oriented Design
3Programming in the Small and Programming in the
Large
4Chapter 3 Object-Oriented Design
- Software development
- Ultimate goal deliver software products that are
oriented towards - Customer satisfaction
- Customer delight
- Customer ecstasy
5- Popular software development methodologies
- System Development Life Cycle (SDLC) Model
- Prototyping Model
- Rapid Application Development Model
- Component Assembly Model
6System Development Life Cycle (SDLC) Model
- System/Information
- Engineering and Modeling
2. Software Requirement Analysis
3. System Analysis and Design
4. Code Generation/ Implementation
5. Testing
6. Maintenance
7Prototyping Model
- A cyclic version of the linear model
- Once the requirement analysis is done and the
design for a prototype is made, the development
process gets started to create a prototype - Once the prototype is created, it is given to the
customer for evaluation - Many iterations between customers feedback and
developers refinement until the final software
package is delivered - In this methodology, the software is evolved as a
result of periodic shuttling of information
between the customer and developer - Popular development model in the contemporary IT
industry - as it is very difficult to comprehend
all the requirements of a customer in one shot - New versions of a software product evolve as a
result of prototyping
8Prototyping Model( many versions)
or
9Rapid Application Development (RAD) Model
- A "high speed" adaptation of the linear
sequential model - Achieved by using a component-based construction
approach - The RAD approach encompasses the following
phases - Business modeling
- The information flow among business functions is
modeled in a way that answers the following
questions - What information drives the business process?
- what information is generated?
- Who generates it?
- where does the information go?
- who processes it?
- Data modeling
- The information flow defined as part of the
business modeling phase is refined into a set of
data objects that are needed to support the
business - The characteristic (called attributes) of each
object is identified and the relationships
between these objects are defined
10Rapid Application Development (RAD) Model (Cont.)
- Process modeling
- The data objects defined in the data-modeling
phase are transformed to achieve the information
flow necessary to implement a business function - Processing the descriptions are created for
adding, modifying, deleting, or retrieving a data
object - Application generation
- The RAD model assumes the use of the RAD tools
like VB, VC, Delphi etc... rather than creating
software using conventional third generation
programming languages - The RAD model works to reuse existing program
components (when possible) or create reusable
components (when necessary) - In all cases, automated tools are used to
facilitate construction of the software - Testing and turnover
- Since the RAD process emphasizes reuse, many of
the program components have already been tested.
This minimizes the testing and development time
11Component Assembly Model
- Object technologies provide the technical
framework for a component-based process model for
software engineering - The object oriented paradigm emphasizes the
creation of classes that encapsulate both data
and the algorithm that are used to manipulate the
data - If properly designed and implemented, object
oriented classes are reusable across different
applications and computer based system
architectures - Component Assembly Model leads to software
reusability. The integration/assembly of the
already existing software components accelerate
the development process - Nowadays many component libraries are available
on the Internet. If the right components are
chosen, the integration aspect is made much
simpler
12What/Why is Software Design
- Software design sits at the crossroads of all the
computer disciplines hardware and software
engineering, programming, human factors research,
ergonomics. It is the study of the intersection
of human, machine, and the various
interfacesphysical, sensory, psychologicalthat
connect them --- by Association for Software
Design (ASD) members - Design is conscious
- Design keeps human concerns in the center
- Design is a dialog with materials
- Design is creative
- Design is communication
- Design is a social activity
- Design has social consequences
13Basis for Design
- Consider for the moment what aspects of a problem
(i.e., to develop a system) are known first - Data Structures
- Functions
- A Formal Specification
- Behavior
- A design technique based on behavior can be
applied from the very beginning of a problem,
whereas techniques based on more structural
properties necessarily require more preliminary
analysis
14Design Notations/Modeling Languages
- Many artifacts generated during the process of
software development - Requirement specifications
- Design documents
- Source code
- User manual
- Design notations capture design documents
- Informal (natural languages)
- Unified Modeling Languages (UML, semi-formal)
- Formal (formal methods, architecture description
languages)
15Object-Oriented Design Techniques/Methods
- Object-Oriented Development (OOD)/Booch
- Hierarchical Object-Oriented Design (HOOD)
- The Object Modeling Technique (OMT)
- Responsibility-Driven Design (RDD)/Class-Responsib
ility-Collaboration (CRC) - Object-Oriented Analysis (OOA)
-
16Object-Oriented Development (OOD)/Booch
- Define the problem
- Develop an informal strategy for the software
realization of the real world problem domain - Formalize the strategy
- Identify the classes and objects at a given level
of abstraction - Identify the semantics of these classes and
objects - Identify the relationships among these classes
and objects - Implement these classes and objects
17Object-Oriented Development (OOD)/Booch (Cont.)
- Major advantages
- Rich notation available
- class diagrams (class structure - static view)
- object diagrams (object structure - static view)
- state transition diagrams (class structure -
dynamic view) - timing diagrams (object structure - dynamic view)
- module diagrams (module architecture)
- process diagrams (process architecture)
18Object-Oriented Development (OOD)/Booch (Cont.)
A Booch Class Diagram for a Company
19The Object Modeling Technique (OMT)
- A method which leads to three models of the
system corresponding to three different views of
the system - The object model
- Describes the static structure of the objects in
a system and their relationships - Main concepts are class, attribute, operation,
inheritance, association (i.e. relationship),
aggregation - The dynamic model
- Describes the aspects of the system that change
over time - Used to specify and implement the control aspects
of a system - Main concepts are state, sub/super state, event,
action, activity - The functional model
- Describes the data value transformations within a
system - Main concepts are process, data store, data
flow, control flow, actor (source/sink)
20The Object Modeling Technique (OMT)(Cont.)
- The method is divided into four phases, which are
stages of the development process - Analysis
- The building of a model of the real world
situation, based on a statement of the problem or
user requirements - System design
- The partitioning of the target system into
subsystems, based on a combination of knowledge
of the problem domain and the proposed
architecture of the target system (solution
domain) - Object design
- Construction of a design, based on the analysis
model enriched with implementation detail,
including the computer domain infrastructure
classes - Implementation
- Translation of the design into a particular
language or hardware instantiation, with
particular emphasis on traceability and retaining
flexibility and extensibility
21The Object Modeling Technique (OMT)(Cont.)
An Object Model of a Company
22Responsibility Driven Design (RDD)
- Developed as Rebecca Wirfs-Brock
- One of object-oriented design techniques, driven
by an emphasis on behavior at all levels of
development - A design technique that has the following
properties - Can deal with ambiguous and incomplete
specifications - Naturally flows from Analysis to Solution
- Easily integrates with various aspects of
software development
23Responsibility Driven Design (RDD)
- Describing the actions and activities for which
our software is responsible - Describing the responsibilities in terms that
both users and developers can understand - Designing software objects that implement those
responsibilities
24Responsibility Driven Design (RDD)
- RDD is not a sequential process
- Steps in RDD
- Software components
- Formalize interfaces
- Designing and representations
- Implementing components
- Integration of components
- Maintenance and evolution
25Case Study the IIKH
- Briefly, the Intelligent Interactive Kitchen
Helper (IIKH) will replace the box of index cards
of recipes in the average kitchen
26Your Job
- Imagine you are the chief software architect
- Your job is to develop the software that will
implement the IIKH
27Abilities of the IIKH
- Here are some of the things a user can do with
the IIKH - Browse a database of recipes
- Add a new recipe to the database
- Edit or annotate an existing recipe
- Plan a meal consisting of several courses
- Scale a recipe for some number of users
- Plan a longer period, say a week
- Generate a grocery list that includes all the
items in all the menus for a period
28Characterization by Behavior
- Just as an Abstract Data Type is characterized
more by behavior than by representation, the goal
in using Responsibility Driven Design will be to
first characterize the application by behavior - First capture the behavior of the entire
application - Refine this into behavioral descriptions of
subsystems - Refine behavior descriptions into code
- This emphasis on behavior is a hallmark of
Object-Oriented programming
29Working Through Scenarios
- Because of the ambiguity in the specification,
the major tool here used to uncover the desired
behavior is to walk through application scenarios
- Pretend there is already a working application
- Walk through the various uses of the system
- Establish the look and feel'' of the system
- Make sure uncover all the intended uses
- Develop descriptive documentation
- Create the high level software design
- The term use-cases'' used for this process of
developing scenarios by others
30Example Browsing Scenario
- Alice Smith starts the IIKH
- IIKH displays welcome message
- Alice presses the return button to begin
- Alice is given a choices of a number of options
- Alice selects to browse recipe
- Alice enters keywords to search, e.g., salmon,
dill weed - IIKH return two results
- Alice selects the first
- IIKH displays a window, showing everything
regarding the recipe - Alice does not want the recipe, returns to the
search result page - Alice selects the second recipe
- Alice wants the recipe
- Alice selects quit from the IIKH program menu
- The IIKH program quits
31Software Components
- A software component is simply an abstract design
entity with which we can associate
responsibilities for different tasks - May eventually be turned into a class, a
function, a module, or something else - A component must have a small well defined set of
responsibilities - A component should interact with other components
to the minimal extent possible
32CRC (Component, Responsibility, Collaborator)
Cards
- Components are most easily described using CRC
cards - A CRC card records the name, responsibilities,
and collaborators of an component - Inexpensive, Erasable, Physical
33The first component, The Greeter
- Let us return to the development of the IIKH. The
first component your team defines is the Greeter - When the application is started, the Greeter puts
an informative and friendly welcome window (the
greeting) on the screen - Offer the user the choice of several different
actions - Casually browse the database of recipes
- Add a new recipe
- Edit or annotate a recipe
- Review a plan for several meals
- Create a plan of meals
- Many of the details concerning exactly how this
is to be done can be ignored for the moment
34The Greeter
35The Recipe Database Component
- Ignoring the planning of meals for the moment,
your team elects to next explore the recipe
database component - Must maintain the database of recipes
- Must allow the user to browse the database
- Must permit the user to edit or annotate an
existing recipe - Must permit the user to add a new recipe
36The Who/What Cycle
- As we walk through scenarios, we go through
cycles of identifying a what, followed by a who - What action needs to be performed at this moment
- Who is the component charged with performing the
action - Every what must have a who, otherwise it simply
will not happen - Sometimes the who might not be obvious at first,
i.e., who should be in charge of editing a
recipe?
37Postponing Decisions
- Many decisions, such as the method of browsing,
can be ignored for the moment, as they are
entirely encapsulated within the recipe database
component, and do not effect other components - Scroll bars and windows?
- A virtual book'' with thumb-holes and flipping
pages? - Keywords and phrases?
- Only need to note that somehow the user can
manipulate the database to select a specific
recipe
38Responsibilities of a Recipe
- We make the recipe itself into an active data
structure. It maintains information, but also
performs tasks - Maintains the list of ingredients and
transformation algorithm (i.e., ingredients to
final product) - Must know how to edit these data values
- Must know how to interactively display itself on
the output device - Must know how to print itself
- We will add other actions later (ability to scale
itself, produce integrate ingredients into a
grocery list, and so on)
39The Planner Component
- Returning to the greeter, we start a different
scenario. This leads to the description of the
Planner - Permits the user to select a sequence of dates
for planning - Permits the user to edit an existing plan
- Associates with Date object
40The Date Component
- The Date component holds a sequence of meals for
an individual date - User can edit specific meals
- User can annotate information about dates
(''Bob's Birthday'', Christmas Dinner'', and so
on) - Can print out grocery list for entire set of
meals
41The Meal Component
- The Meal component holds information about a
single meal - Allows user to interact with the recipe database
to select individual recipes for meals - User sets number of people to be present at meal,
recipes are automatically scaled - Can produce grocery list for entire meal, by
combining grocery lists from individual scaled
recipes
42The Six Components
- Having walked through the various scenarios, you
team eventually decides everything can be
accomplished using only six software components - You can at this point assign the different
components to different programmers for
development
43Interaction Diagrams
- The picture on the previous slide captures static
relationships, but not the dynamic flow of
messages in a scenario - That information can be recorded by an
interaction diagram
44Characteristics of Components
- Let us return to the idea of a software component
- There are many different aspects to this simple
idea, we will consider just a few - Behavior and state
- Instances and classes
- Coupling and cohesion
- Interface and implementation
45Behavior and State
- All components can be characterized by two
aspects - The behavior of a component is the set of actions
a component can perform. The complete set of
behavior for a component is sometimes called the
protocol - The state of a component represents all the
information (data values) held within a component -
- Notice that it is common for behavior to change
state. For example, the edit behavior of a recipe
may change the preparation instructions, which is
part of the state
46Instances and Classes
- We can now clarify a point we earlier ignored.
There are likely many instances of recipe, but
they will all behave in the same way. We say the
behavior is common to the class Recipe
47Coupling and Cohesion
- The separation of tasks into the domains of
different components should be guided by the
concepts of coupling and cohesion -
- Cohesion is the degree to which the tasks
assigned to a component seem to form a meaningful
unit - Want to maximize cohesion
- Coupling is the degree to which the ability to
fulfill a certain responsibility depends upon the
actions of another component - Want to minimize coupling
48Interface and Implementation
- We have characterized software components by what
they can do - The user of a software component need only know
what it does, not how it does it - Ask not what you can do to a data structure, ask
instead what your data structures can do for
you''.
49Two views of a Software System
- This naturally leads to two views of a software
system - The term information hiding is used to describe
the purposeful hiding of implementation details
50Parnas' Principles
- These ideas were captured by computer scientist
David Parnas in a pair of rules, which are known
as Parnas' Principles - The developer of a software component must
provide the intended user with all the
information needed to make effective use of the
services provided by the component, and should
provide no other information - The implementer of a software component must be
provided with all the information necessary to
carry out the given responsibilities assigned to
the component, and should be provided with no
other information
51Public and Private View
- In C and Java, Parnas's Principles lead to the
ideas of a public and private view - Public view - those features (data or behavior)
that other components can see and use - Private view - those features (data or behavior)
that are used only within the component
52Next Step - Formalize the Interface
- The next step is to formalize the channels of
communication between the components - The general structure of each component is
identified - Components with only one behavior may be made
into functions - Components with many behaviors are probably more
easily implemented as classes - Names are given to each of the responsibilities -
these will eventually be mapped on to procedure
names - Information is assigned to each component and
accounted for - Scenarios are replayed in order to ensure all
data is available
53Names with Activities
- The selection of names is an important task
- Names should be evocative in the context of the
problem - Names should be short
- Names should be pronounceable (read them out
load) - Names should be consistent within the project
- Avoid digits within a name
54Documentation
- Besides CRC cards, it is important that the
development of other documentation be performed
almost from the beginning - The two most important documents are the user
manual and the design documentation of the
software system
55User Manual
- The user manual describes the application as seen
by the user - Does not depend upon the implementation, so can
be developed before the implementation - Can naturally flow from the process of walking
through scenarios - Can be carried back to the clients to make sure
the users and the implementers have the same
ideas
56Quality
- You should always remember that the primary
measure of quality is the degree to which your
customers (clients) are satisfied with your
product - Since often customers do not know exactly what it
is they want, it is important to work with the
client early in the design phase to make sure the
system your are developing is the desired product - One very important way to do this is to create
the user manual even before the software is
written
57System Design Documentation
- Record the decisions made during the process of
system design - Record the arguments for and against any major
decision, and the factors influencing the final
choice - Record CRC cards for the major components
- Maintain a log or diary of the process schedule
- Important to produce this while the ideas are
fresh, not in hindsight when many details will
have been forgotten - Note the code only records the outcome of
decisions, not factors that lead up to decisions
being made
58Preparing for Change
- Your design team should also keep in mind that
change is inevitable - Users requirements change with experience,
hardware changes, government regulations change - Try to predict the most likely sources of change,
and isolate the effect - Common changes include interfaces, file formats,
communication protocols - Isolate interfaces to hardware that is likely to
change - Reduce dependency of one software component on
another - Keep accurate record of the reasoning behind
every major decision in the design documentation
59Next Step - Select Representations for Subsystems
- Next the internal representation of the software
subsystem corresponding to each component is
selected -
- Knowledge of the classic data structures of
Computer Science is important here - Often once data structures have been selected,
the code is almost self-evident
60Next Step - Implement and Test Subsystems
- Classic techniques, such as stepwise refinement,
are used to implement each of the subsystems - Subsystems are validated in isolation
- Informal proofs of correctness for the subsystem
are developed - Identify necessary conditions for correct
functioning. Try to minimize conditions, and test
input values whenever possible - Software testing is used as a confidence building
measure
61Step - Integration and Testing
- Components are slowly integrated into completed
system - Stubs can be used to perform testing all during
integration -
- Errors discovered during integration to cause
reinvestigation of validation techniques
performed at the subsystem level
62Maintenance and Evolution
- Software does not remain fixed after the first
working version is released - Errors or bugs can be discovered. Must be
corrected - Requirements may change. Say as a result of
government regulations, or standardization among
similar products - Hardware may change
- Users expectations may change. Greater
functionality, more features. Often as a result
of competition from similar products - Better documentation may be required.
- A good design recognizes the inevitability of
change, and plans an accommodation for these
activities from the very beginning
63Common Design Flaws
- The following categories present some of the more
common design flaws - Direct modification
- Components that make direct modification of data
values in other components are a direct violation
of encapsulation - Such coupling makes for inflexible designs
- Too Much Responsibility
- Components with too much responsibility are
difficult to understand and to use - Responsibility should be broken into smaller
meaningful packages and distributed - No Responsibility
- Components with no responsibility serve no
purpose - Often arise when designers equate physical
existence with logical design existence - Money is no object''
- Components with unused responsibility
- Usually the result of designing software
components without thinking about how they will
be used - Misleading Names
- Names should be short and unambiguously indicate
what the responsibilities of the component
involve