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CS 501: Software Engineering. Lecture 9 Requirements 3. Course Administration. Feasibility Study Everybody should have receive comments. Teaching Assistants have been assigned. Remember to send your weekly reports. Quiz 1 - PowerPoint PPT Presentation
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1 CS 501 Spring 2007
CS 501: Software Engineering
Lecture 9
Requirements 3
2 CS 501 Spring 2007
Course Administration
Feasibility Study
Everybody should have receive comments.
Teaching Assistants have been assigned.
Remember to send your weekly reports.
Quiz 1
Uncollected answer books are at the reception at 301 College Avenue.
3 CS 501 Spring 2007
Discussion of Feasibility Study
General
Who will read the feasibility study?What is needed to decide to go ahead?
Scope and understanding of project
Statement of the task Preliminary requirements and technical analysisDeliverables and business considerations
Confidence
Outline plan. Does it inspire confidence?Visibility plan. How will progress be reported? Risk analysis. How are the risks to be minimized?
4 CS 501 Spring 2007
Course Administration
Assignment 2, First Milestone, March 6-8
Read information on the Assignments Web page
Reserve time for your presentation. See the home page of the Web site.
i Client must be present
ii Not all team members must be present, but each team member must make a presentation at least once
during the semester
iii Try to find a time when the TA can be present
5 CS 501 Spring 2007
Course Administration
Assignment 2, First Milestone, March 6-8
• One third of the total work from the feasibility study.
• If you are following an iterative process, this is a major milestone when you can report visible progress to your client. Typically, this will include a first set of requirements, a provisional design and a prototype that can be used to demonstrate the functionality of the system, including user interface design.
• If you are following a modified waterfall process, this progress report should include completion of the requirements phase and perhaps the first steps in the design.
6 CS 501 Spring 2007
Software Development Principles and Practices
Software development
Software development is a craft. Software developers have a variety of tools that can be applied in different situations.
Part of the art of software development is to select the appropriate tool for a given implementation
7 CS 501 Spring 2007
Modeling Techniques for Requirements Analysis and Definition
The craft of requirements analysis and specification is to select the appropriate tool for the particular task.
• A variety of tools and techniques.
• Many are familiar from other courses.
• There is no correct technique that fits all situations.
As you build understanding of the requirements through scenarios and use cases, use modeling tools to specify requirements. The models provide a bridge between the client's understanding and the developers.
8 CS 501 Spring 2007
Decision Table: Bad Example
University Admission Decision
Note that the rules are too vague.
High SAT T F F F F F
High grades - T F F F F
Sports - - T T F F
Recommendations - - T F T F
Reject X X X
Accept X X X
9 CS 501 Spring 2007
Decision Table: Good Example
University Admission Decision
Note that the rules are now specific and testable.
SAT > S T F F F F F
GPA > G - T F F F F
Athletics code = - - T T F F
Recommendations > A- - - T F T F
Send rejection letter X X X
Send acceptance letter X X X
10 CS 501 Spring 2007
Data-Flow Models
External entities
Processing steps
Data stores or sources
Data flows
An informal modeling technique to show the flow of data through a system.
11 CS 501 Spring 2007
Data-Flow Example: University Admissions (first try)
Applicant
Applicationform Receive
application
Completedapplication
Evaluate
Rejection
Acceptance
Shows the flow, but where is the data stored?
12 CS 501 Spring 2007
Data-Flow Example: Assemble Application Stage
Applicant
Applicationform
Receive
Completedapplication
Supportinginformation
Pendingdatabase
Acknowledgment
Beginevaluation
Applicantdatabase
Evaluationrequest
AND
AND
Acknowledgment
Does this model cover all applications? Are there special cases?
13 CS 501 Spring 2007
Data-Flow Example:Process Completed Application Stage
Rejection
Evaluation
Applicantdatabase
Evaluationrequest Acceptance Financial
aid
Offer
Specialrequest
The data-flow diagram will need specification of the decision-making process.
14 CS 501 Spring 2007
Procedural Models: Flowchart
Operation
Decision
Manual operation
Report
An informal modeling technique to show the decisions and paths that data takes through a system.
15 CS 501 Spring 2007
Flowchart: University Admissions
Form received New?
Database record
T
Notify student
F Update database
Complete?
Notify student
T
FEvaluate
16 CS 501 Spring 2007
Procedural Models: Pseudo-code
Example: Check project plan
check_plan (report)
if report (date_time) > due_date_time then error (too_late) if report (client) = none then error (no_client) if report (team) < min_team or > max_team then error (bad_team) if error() = none then comments = read_report (report) return (comments (text), comments (grade)) else return error()
An informal modeling technique to show the logic behind part of a system.
17 CS 501 Spring 2007
Transition Diagrams
A system is modeled as a set of states, Si
A transition is a change from one state to another.
The occurrence of a condition, Ci, causes the transition from one state to another
Transition function:
f (Si, Cj) = Sk
Example S1 S2
S30
0
0
1
11
18 CS 501 Spring 2007
Transition Diagram for CS 501 Web Site
home
syllabus projects booksassign-mentsquizzes integrity about
slides surveysconcepts exam-ples
19 CS 501 Spring 2007
Therapy Control Consol: Finite State Machine
Example: Radiation Therapy Control Console
You are developing requirements for the operator's control console. In a client interview, the client describes the dangers inherent in using the machine.
The operator must follow a strict procedure before the machine is ready to run.
You use a finite state machine to specify the procedures. This shows the client that you understand the requirements and specifies the procedures for the developers.
20 CS 501 Spring 2007
Therapy Control Consol: Scenario
"The set up is carried out before the patient is made ready. The operator selects the patient information from a database. This provides a list of radiation fields that are approved for this patient. The operator selects the first field. This completes the set up.
"The patient is now made ready. The lock is taken off the machine and the doses with this field are applied. The operator then returns to the field selection and chooses another field."
21 CS 501 Spring 2007
State Transition Diagram
Patients Fields Setup ReadyBeam
on
Enter Enter Start
Stop
Select field
Select patient(lock on)
(lock off)
Discuss each state and transition with the client.
22 CS 501 Spring 2007
Therapy Control Consol: State Transition Table
SelectPatient
SelectField
Enter lock off Start Stop lock on
Patients
Fields
Setup
Ready
Beamon
Fields
Fields
Fields
Patients
Patients
Patients
Setup
Setup
Setup
Ready
Beamon
Ready
23 CS 501 Spring 2007
Entity-Relation Model
A requirements and design methodology for relational databases
• A database of entities and relations
• Tools for displaying and manipulating entity-relation diagrams
• Tools for manipulating the database (e.g., as input to database design)
Warning: There is much confusion about definitions and notation
24 CS 501 Spring 2007
Entity-Relation Diagram
An entity
A relation between entities
An entity or relation attribute
An inheritance relation
25 CS 501 Spring 2007
Example: CS 501 Project
Student
CS501 Student
Major
Project
5 to 7
1
Member of
Client team member
Client1:n
Tech contact
0:n0:1
0:1
26 CS 501 Spring 2007
Example: Schema for Web Data
CS 501 Spring 2005
27 CS 501 Spring 2007
Part of an Entity-Relation Diagram for a Book Catalog
Book
Short title
Catalog record
Describes
Control numb
Subject heading
Is about
CreatorEditor of
Author of
1:n
1
0:n
0:n
0:n
0:n
0:n
1
28 CS 501 Spring 2007
Data Dictionaries
A data dictionary is a list of names used by the system
• Name (e.g., "start_date")
• Brief definition (e.g., what is "date")
• What is it? (e.g., integer, relation)
• Where is it used (e.g., source, used by, etc.)
• May be combined with a glossary
As the system is implemented, the data dictionary in the requirements is input to the system data dictionary, which is a formal part of the system specification.
29 CS 501 Spring 2007
Petri Nets
A Petri Net models parallelism
A
S1
Sm
S
S
A
Event 1
Event n
Event
A
Event 1
Event n
..
f(A; E) S
f(A; E1,..,En) S
f(A; E1,..,En) S1,..,Sm
30 CS 501 Spring 2007
Prototyping Requirements
Rapid prototyping is the most comprehensive of all modeling methods
A method for specifying requirements by building a system that demonstrates the functionality of key parts of the required system
Particularly valuable for user interfaces
31 CS 501 Spring 2007
A Note on Object Models
This course teaches object models as a tool for design.
Some people recommend object models for requirements definition, but it is difficult to use them without constraining the system design.
Flow charts and finite state machines are supported by UML as design models, but can also be used for requirements.
*