cs 451 software engineering
TRANSCRIPT
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CS 451 Software Engineering
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Yuanfang Cai
Room 104, University Crossings
215.895.0298
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Design Engineering A systematical way to “translate” SRS into
design Start with use cases from SRS Find analysis classes from use cases
Create CRC cards from use cases Refine CRC cards into UML class diagrams Different types of classes
Architecture Design Interface Design Component Design Detailed/Data Design
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From Use Cases to Class diagrams
Step 1: Identify and assign candidate classes Step 2: Determine a set of specific scenarios Step 3: Walk through the scenario, naming cards
and responsibilities
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Step 1: Identify and assign candidate classes Read requirements specification.
Highlight nouns and noun phrases to give
candidate classes (excluding abstract nouns).
Write each candidate class down on an index card.
Assign each index card to one person who is participating in the CRC card modelling session.
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Consists of classes of domain objects. Example: any ATM model will involve Card,
BankAccount classes Names are important.
Class identification is a key process for a good class model: noun identification; responsibility driven approach.
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Step 1: Identify and assign candidate classes
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Noun identification Two stages:
identify candidate classes by picking all nouns and noun phrases out of requirements specification document;
discard inappropriate candidates. A candidate is an inappropriate class when it is
redundant (ex: book, book in many volumes; member of the library,library member)
vague (item it may be either book or journal etc) an event or an operation (a loan – an event: lending a book) meta-language element: used to describe and explain requirements
and the system at a very high level (system, rule, information, or reporting requirements)
outside the scope of the system (time) an attribute (name) Nouns are outlined
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CRC Cards
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Introduction to CRC Cards CRC Card = Class Responsibility Collaborator
Card
Purpose: interactively brainstorm an initial design of a program or program segment
Invented in 1989 by Kent Beck and Ward
Cunningham
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CRC Cards Class – the name of an OO class (a good descriptive noun) Responsibility – the things the OO class does (behavior responsibility) Collaborator – the relationship the class has with other classes
Class Name Main Responsibility Responsibilities Collaborators . . . . . .
4 X 6 (or 3 X 5)
Index card
Some also suggest writing down the classes properties (what the class must know about itself – knowledge responsibility) on the back of the card
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An Example CRC Card - Front
Main Responsibility
A patient makes appointments, review or configure insurance information, and provides medical history
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An Example CRC Card - Back
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Step 2: Determine a set of specific scenarios Develop a comprehensive and specific set of
end-to-end scenarios based upon the requirements. A scenario is a sequence of actions that illustrates
behavior.
Example: Requirement: The alarm clock shall allow a user to
set the time. Scenario: The user sets the time for 1:15PM.
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Step 3: Walk through the scenario, naming cards and responsibilities
Walk through the handling of a scenario case pointing to or picking up the cards, naming their responsibilities and how they handle and delegate each request.
Add new cards as classes are needed.
Note: It’s always good to do very basic/mainstream use cases first, then explore alternative/complicated use cases.
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An ATM Example See Class Exercise
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ATM –All Nouns
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ATM- Classes Class candidates:
card bank account (ATM) dispenser & session – vague (it might become of interest)
Data associated PIN - attribute of card current balance - attribute of bank account amount – attribute in various classes overdraft limit – attribute of bank account card limit per day – attribute of card dispenser amount – attribute of ATM dispenser
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ATM Example:
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More ATM CRC Cards
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ATM –Card Class
Card class’ attributes and operations; validatePIN() validates the PIN introduced against the value in pin; changePIN() changes the current pin value with what this operation provides; startWithdraw() initiates the withdrawal by i) checking that the amount requested is
within dayLimit range; ii) checks with BankAccount that there is enough in the current bank account or the overdraft limit is sufficient for this transaction; iii) it also checks that there is enough cash in dispenser; if all these are fulfilled it asks BankAccount to update the balance and Dispenser to release the cash.
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ATM –BankAccount Class
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ATM –Dispenser class
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ATM Transaction Class
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ATM additional requirements Let’s consider that transactions involving cash withdrawal, either
failed or successful, are recorded. In this case session (retained as vague) will be reconsidered and Transaction is
the class that will be identified for session. Reconsider CRC cards: when Card class will initiate cash
withdrawal then another collaboration will be added, i.e. Transaction class will record this transaction.
A new CRC card will be then generated for Transaction class.
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CRC Cards Relationship
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ATM –Class Diagram
Class diagrams is obtained directly from CRC cards by considering collaborations identified; it shows business classes.
Classes are shown with no attributes and operations.
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ATM-Refined Class Diagram
For each Card there is one bank account, one dispenser and an arbitrary number of transactions.
Each BankAccount should have one or more cards associated with. The Dispenser refers to all cards. Each Transaction has a unique card on it. All associations are named, directed and unidirectional.
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Different types of analysis classes Entity Class
Data Structures: e.g. Card, Process Class
Classes that work: Transactions Boundary Class
Interface with external systems: Dispenser
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Clear Intersection Example From the Use Cases to Design
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1. Flow of Events for the Clear Intersection Use Case 1.1 Preconditions Traffic light has been initialized. 1.2 Main Flow This use case begins when a car enters the intersection. The car checks it’s status (S-1). The use case ends when the car clears the intersection (S-4). 1.3 Subflows S-1 Check Status Check status (S-2, S-3). If the light is green, and the queue is empty, the car clears the intersection (S-4). Otherwise, it joins a queue (S-5). S-2 Check Light Get information on whether the light is red, yellow, or green. S-3 Check Queue Get information on whether the queue is empty or not S-4 Go The car clears the intersection and the use case ends. S-5 Join a Queue Car is added to queue.
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Step 1: Identify and assign candidate classes The Clear Intersection use case:
“This use case begins when a car enters the intersection. The car checks it’s status (S-1). The use case ends when the car clears the intersection (S-4).”
“Check status (S-2, S-3). If the light is green, and the queue is empty, the car clears the intersection (S-4). Otherwise, it joins a queue (S-5).”
Candidate Classes Car Traffic light Queue Intersection
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Step 2: Determine a set of specific scenarios-From Use Cases Scenarios
The car can only drive through the intersection if the traffic light is green and there are no cars in the intersection.
Otherwise, the car needs to join a queue.
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Step 3: Walk through the scenario, naming cards and responsibilities Index Card: Car Responsibility
Drive Join
Collaborator Traffic light Queue Intersection Car
Car approaches the intersection and the light is green and there are no cars in the way.
Car approaches the intersection and the
light is red.
Car is in the queue and the light turns green.
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CRC Cards What next?
Class Name Main Responsibility Responsibilities Collaborators . . . . . .
4 X 6 (or 3 X 5)
Index card
Turn these cards into your class diagram Responsibilities --- Methods Collaborators --- Associations (need to have instances of
collaboration classes) Data members on the card back --- Attributes.
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The Design of Traffic Simulator
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Final Implemention Process Class: 255 LOC
Car.java: 31 LOC CarQueue.java: 51 LOC CarQueueCollection.java: 52 LOC Direction.java: 13 LOC LightCollection.java: 31 LOC LightColor.java: 7 LOC TrafficController.java 70 LOC
UI class: Traffic.java: 251 LOC Including menu, car queue initialization, etc.
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Design Engineering Start with use cases from SRS Find analysis classes from use cases
Create CRC cards from use cases Refine CRC cards into UML class diagrams Different types of classes
Architecture Design Interface Design Component Design Detailed/Data Design
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The Design of Traffic Simulator
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Data Model Design Why Data Model Design is needed?
Performance consideration Interface consideration Adaptability consideration
Different types of Data Design In-memory data structure Input-output file format Database scheme Classes attributes
Principles: abstraction and modularization 38
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Data Modeling Concepts Data objects can then be represented as tables:
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Data Modeling Concepts Data attributes define properties of a data object. RELATIONSHIPS Data objects connect to one another in different ways.
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Data Modeling using Classes
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The Data Model Design of TheraWii
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Database Scheme Design Entity Relation Diagram
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The Database Design of Vodka
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Interface Design Why interface design is needed?
Task parallelism Performance analysis
Different types of Interface Design Graphical interface design Boundary class design Database interface design File storage interface design Hardware interface design More…
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The Component and Interface Design of TheraWii
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Software Design Document Syntax Component Diagram
High-level Component Diagrams Detailed Component Diagrams (Classes and relations
within a Component) Interface Design (Boundary Class) Data Model /Data Storage Design (Entity
Classes), data attributes have to be specified Other models
Deployment Diagram Algorithm Explanation
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