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CS 551 – Requirements and Prototyping
Thanks to Rand Edwards and Ian Summerville for this material
Software Requirements Process
Requirements Elicitation Requirements Analysis Use Cases Requirements Specification Prototype Requirements Management
Requirements Specification Spec
1. Project Title, Revision Number and Author2. Scope and Purpose of the system3. Measurable Operational Value4. Description5. Feature List including ICED T and Simplified QFD
analysis6. Interfaces7. Constraints8. Change Log and Expected Changes9. Responses to the unexpected10. Measurements11. Glossary12. References
QSE Characteristics
Solving the right problem the right way Certified against requirements. Certified against problem Bounded execution domain
Trustworthy Software is:
Safe: Does no harm Reliable: No crash or hang. Secure: No Hacking Possible
QSE Lambda Protocol
Prospectus Measurable Operational Value Prototyping or Modeling sQFD Schedule, Staffing, Quality Estimates ICED-T Trade-off Analysis
Universal Software Engineering Equation
Reliability (t) = ℮ -k t
when the error rate is constant and where k is a normalizing constant for a software shop and
= Complexity/ effectiveness x staffing
Case Study: SchedulerPro Prospectus
User friendly, efficient interface for students to create and modify class schedules.
Features:• Visual schedule creation and editing
• Schedule suggestion
• Schedule comparison view
• Monitor closed-out sections
SchedulerPro Prototype Screen
SchedulerPro Prototype Screen
SchedulerPro Notification Emails
Measurable Operational Value SchedulerPro MOV
Course scheduling and registration time reduced by an average of 20 minutes per student per semester.
SchedulerPro Functional Goals
Schedule Classes and Personal Time
Searching
Course Placement
Course Detail Viewing
Course Removal
Scheduling Personal Blocks
Notification (optional)
Course Suggestions (optional)
SchedulerPro Functional Requirements
• Search available classes by: Same professor Similar time Same or equivalent class but different sections
• Register and track registrations
• Color classes and arbitrary time-blocks by user choice
SchedulerPro Nonfunctional Requirements
• Integrate with “Web for Students’ and existing authentication systems and avoid incompatibilities
• Allow schedules to be saved/accessed from a server or local file
• Provide a scaled time-accurate visual representation of the schedule
More Non-functional requirements
Make schedules available even if the application is down, provided an internet connection is available
Perform some functions without a live connection to the ‘Web for Students’ registrar web site
Make compatible with all popular browsers• Display section states and print schedules without
loss of detail
SchedulerPro sQFD
Features / Functions
Class FiltersAllocate non-class
timeLong term information
availabilityAuthenticate
Makes scheduling classes easier 8 3 6 2 19
Makes scheduling a semester easier
7 9 8 2 26
Find schedules in one place 1 1 5 7 14
Total 16 13 19 11 59
SchedulerPro Product Reliability
Two hours of unavailability allows for daily backups, service, and reboots of the system
Connections to server are minimized, reducing overall activity on the server
Jan. Function Point Est.
Function Low (L) Average (A) High (H) Total
Outputs 1 3 0 19
Inquiries 8 4 1 49
Inputs 5 7 1 41
Internal Files 3 2 0 24
External Interfaces 2 1 0 10
Total UFP 143
Adjustment Factor 0.99
Total AFP 141
April Function Points Est.Function Low Average High Total
Outputs 1 0 1 9
Inquiries 3 0 0 9
Inputs 2 3 0 18
Internal Files 3 1 0 31
External Interfaces 1 1 0 12
Total UFP 79
AFP 82
History of Function Points
Date AFP Project Length*
Projected Finish*
January 27 141 19.7 staff months
August 2006
February 24 104 14.4 staff months
March 2006
April 17 82 8.5 staff months
May
2006
*Using COCOMO Model
Web PointsFunction Total Web
Objects
Outputs 11
Inquiries 9
Inputs 18
Internal Files 31
External Interfaces 12
# Multimedia files 6
# Web building blocks 7
# Scripts 3
# Links 0
Total Web Objects 97
Effort = A * cdi (Size)P1
Because it is a small web project, assume:
A=2.1, B=2.0, P1=1.00, and P2=.5
Language Expansion Factor = 25
From this, we estimate 2.43 KLOC
Effort = A* KLOC = 2.1 * 2.43
= 5.103= 5.103 staff-months staff-months Duration =B * EffortP2 = 2.0 * 5.103.5
= 4.5184.518 calendar months calendar months
ICED-T
Scheduling by:Intuitive Consistent Efficient Durable Thoughtful
Paper 3 2 2 2 3
Excel 3 2 3 3 3
School Scheduler 3 4 4 3 4
SchedulerPro 4 4 5 4 5
SchedulerPro Creeping Features
Are the System Administrators important stakeholders?
You bet…
Parnas reliability checklist
Failures in communication, secondary storage, memory, or any hardware that may interrupt a transaction:
» The SQL Server DBMS will not commit incomplete transactions. User will be notified of the error, and will have to redo the transaction.
Operator error:» Important operations are confirmed before they are completed to
avoid large accidental errors.
SchedulerPro Estimate of Reliability
R(t) = 1 - F(t) R(t) = 1 - F(t) F(t) = P(T ≤ t)F(t) = P(T ≤ t)
During load testing, we discovered the test server can support 1500 user queries a minute.
P(failures/query) = 55/1500 = 0.036P(failures/query) = 55/1500 = 0.036
Thus, F(t) = 3.6%, which means the software is 96.4% reliable
SchedulerPro Reliability Estimate
1/ λ = MTTF = εE/kC k = scaling constant = 1
C is complexity = 2.78
E is the development effort = 36.4ε is the expansion factor = 1.5
λ = 0.05
t is the continuous execution time for the software
R(t) = 95.12%
Complexity Chart - Client
Project Type: online transaction
Problem Domain: 2 Architecture Complexity: 3 Logic Design – Data: 2 Logic Design – Code: 3
» Total Score: 10
» Complexity = (10/18) * 5 = 2.78
Complexity Chart - Server
Project Type: online transaction
Problem Domain: 1 Architecture Complexity: 2 Logic Design – Data: 2 Logic Design – Code: 2
» Total Score: 7
» Complexity = (7/18) * 5 = 1.94
Complexity Chart - Overall
Project Type: client/server Problem Domain: 2 Architecture Complexity: 3 Logic Design – Data: 2 Logic Design – Code: 3
» Total Score: 10
» Complexity = (10/18) * 5 = 2.78
SchedulerPro Installation Plan
Installation
1. Third Party Software Required
Scheduler Pro requires the following products to be already installed on the target machine. Please consult the documentation of each product for installation instructions specific to each.
- Windows 2000, XP, or 2003 Server- Microsoft IIS, version 5.0 or higher- Microsoft .NET, version 1.1- Microsoft SQL Server 2000- Message Queuing Service (Windows component)- ASP.NET State Service
2. Installing the Scheduler Pro applicationTo install Scheduler Pro, please follow these steps:
I. Setting up the web site1. Create a virtual directory for the site in IIS2. Copy the contents of the “site” folder to the directory on your hard drive represented
by the IIS virtual directoryII. Setting up the database
1. Using the SQL Server Enterprise Manager tool, attach the database located under the “sqldb” directory.2. Create a new user account for accessing this database, and give it read/write access for the database.
III. Installing the Suggest, Notified, and Data Loader Windows ServicesOpen the directory titled “services”. Run each of these files: - InstallSuggestService.exe - InstallNotifierService.exe - InstallDataLoaderService.exe
Each installer will properly install the service. The Data Loader installer willalso ask you for the location and name of the course data file it will load.
SchedulerPro Installation Plan
Requirements Engineering Process
Requirements Document & Validation Report
Requirements ElicitationRequirements Elicitation
Requirements AnalysisRequirements Analysis
Agreed Requirements
Prospectus
Decision Point: Accept Document or re-enter spiral
Requirements SpecificationRequirements Specification
Requirements ValidationRequirements Validation
Prototype
Simple QFD
Baseline Document
Key Question
What’s the problem?
Prospectus & Elicitation
What Information do we need?• Description of the Problem
• Description of the Environment
• Scope of Solution
• A list of project goals
• Any constraints on the behavior or structure of the solution-system
Interviews
Scenarios
Prototypes
Facilitated Meetings
Observation
Elicitation Techniques
Elicitation Challenges
Experts don’t know what they know!• Much knowledge is tacit thru extensive use• Difficult to dig it out• Know-how expressed as solutions
Analysts are domain novices• Tend to simplify • Often miss key functions
Software Requirements
Objective Requirements Elicitation Overview Requirements Analysis Unified Modeling Language
• Use Cases
• Behavioral Modeling
Requirements Engineering Process
Requirements ElicitationRequirements Elicitation
Requirements Analysis & Negotiation
Requirements Analysis & Negotiation
Agreed Requirements
Draft Requirements Document
Requirements Document & Validation Report
Informal Statement of Requirements
Decision Point: Accept Document or re-enter spiral
Requirements SpecificationRequirements Specification
Requirements ValidationRequirements Validation
Process Models Process Actors and
Stakeholders Process Support and
Management Process Quality and
Improvements Relationship to the
Business Decision
Requirements Process - Context
Varied Sources» Different Processes
» Risk Factors Different “Consumers”
» Development
» Marketing
» Training
» Documentation
» Information Base
RequirementsEngineering
Process
BusinessStrategy
BusinessStrategy
TechnologyStrategy
TechnologyStrategy
Project, Process & DocumentationStandards
Project, Process & DocumentationStandards
OpportunityAnalysis
MarketAnalysis
CustomerRequest
SoftwareDesign
SoftwareDevelopment
SoftwareTesting
Requirements Document
Requirements Document
Marketing,Etc.
UML Framework
Source: Martin, James, Odell, James J., Object-Oriented Methods:
A FoundationUML Edition
Prentice-Hall PTR, 1998
Source: Martin, James, Odell, James J., Object-Oriented Methods:
A FoundationUML Edition
Prentice-Hall PTR, 1998
Basic Foundation Level
Types (Concepts)ObjectsMappingsRelationshipsAssociationsSubtypes/SupertypesStates
EventsOperationsMethodsTriggersControl ConditionsState Changes
AggregationConstraintsRules
ClassificationMeta-ModelsPower Types
Extended Foundation Level
StructuralSpecification
BehavioralSpecification
OO ProgramLanguages
… …
ClassDiagram
…ActivityDiagram
…C++
Smalltalk…
Application Level
Use Cases Drive Development
Use Cases
Test Case Design
Architecture and Design
Mapping Requirements to a Framework
Requirements
• Purpose
• Prioritized
• Categorized
• Dependencies resolved
• Quantified
• Bounded
PMO Models
Requirements
ElicitationReports
Use CassUse Cass
ICED-T• Intuitive• Consistent• Efficient• Durable• Thoughtful
ICED T Mappings
Ratings
1 = ‘Worst I have ever seen’
2 = ‘Worse than Average’
3 = ‘Average, like most other systems’
4 = ‘Better than Average’
5 = ‘Best I have ever seen’
Mapping Requirements to a Framework
PMO Models
Requirements
ElicitationReports
Use Cases
Use Cases
Static Structure
Static Structure
Activity Model
Activity Model
UML Framework•Use Case Diagram•Class Diagram•Component Diagram•Activity Diagram•State Chart•Sequence Chart•Timing Chart
Only as needed!
Package Diagram
Groups related use cases Forms basis for a
functional partitioning from the users point of view.
Shorthand for tracking within the project
Order Entry
ViewStatus
Create & Submit Orders
Activity Chart
EnterOrder
CheckCredit
[submitted]
[aborted]
[denied]
AllocateInventory
[approved]
PrepareDelivery
ReceivePayment
Create Order& Submit
<<trace>>
Order Entry Finance FinanceShippingInventory
Management
Simplified QFD (scale 0 to 10)
Goals/Features Track Delivery Trucks
.On-line Customer Inquiry
Credit Check
1. Easy to Order 0 9 3
2. 10% Less Inventory
0 0 0
3. 20% Profit Increase
3 9 9
4. Speed Product Introduction
0 9 0
Total 3 27 12
Required Measurements
Function Points ICED T Consistency = %features with average QFD > 7 Stability = feature changes/month
Prototyping
Prototyping is the rapid development of a system The principal use is to help customers and
developers understand the requirements for the system• Requirements elicitation – Users can experiment with a
prototype to see how the system supports their work• Requirements validation – The prototype can reveal
errors and omissions in the requirements Prototyping can be considered as a risk reduction
activity
Five Great Patterns
Solo Virtuoso
Code Ownership
Engage QA
Divide and Conquer Prototype
Reference: Technical Memorandum by J. O. Coplien Document No. BL0112650-940906-50TM
Product Size Reduction
TRADITIONAL PROCESS PROTOTYPING
40% REDUCTION
20%
80%
40%
30%
45%
25%
SystemsEngineering
Design,Develop,
Test,Install
FinalDevelopment,Deployment
SystemsEngineering &
Prototype
FinalDevelopment
Deployment
As of 8 Sept 05
Prototyping Benefits
Misunderstandings between software users and developers are exposed
Missing services may be detected and confusing services may be identified
A working system is available early in the process The prototype may serve as a basis for deriving a
system specification The system can support user training and system
testing
Approaches to Prototyping
Prospectus
Evolutionaryprototyping
Throw-awayPrototyping
Deliveredsystem
Executable Prototype +System Specification
Prototyping Objectives
The objective of evolutionary prototyping is to deliver a working system to end-users• The development starts with those requirements
which are best understood. The objective of throw-away prototyping is to
validate or derive the system requirements• The prototyping process starts with those
requirements which are poorly understood
Evolutionary Prototyping
Must be used for systems where the requirements specification cannot be developed in advance
Based on techniques which allow rapid system iterations
Verification is impossible as there is no specification
Validation means demonstrating the adequacy of the system
Evolutionary Prototyping
Build prototypesystem
Develop abstractspecification
Use prototypesystem
Deliversystem
Systemadequate?
YES
N
Evolutionary Prototyping Advantages
Accelerated delivery of the system• Rapid delivery and deployment are sometimes more important
than functionality or long-term software maintainability
User engagement with the system• Not only is the system more likely to meet user requirements,
they are more likely to commit to the use of the system
Evolutionary Prototyping
Specification, design and implementation are inter-twined
The system is developed as a series of increments that are delivered to the customer
Techniques for rapid system development are used such as CASE tools and 4GLs
User interfaces are usually developed using a GUI development toolkit
Evolutionary Prototyping Problems
Management problems• Existing management processes assume a waterfall
model of development
• Specialist skills are required which may not be available in all development teams
Maintenance problems• Continual change tends to corrupt system structure so
long-term maintenance is expensive Contractual problems
Prototypes as Specifications
Some parts of the requirements may be impossible to prototype• E.g., safety-critical functions
An implementation has no legal standing as a contract
Non-functional requirements cannot be adequately tested in a system prototype
Incremental Development
System is developed and delivered in increments after establishing an overall architecture
Requirements and specifications for each increment may be developed
Users may experiment with delivered increments while others are being developed• These serve as a form of prototype system
Intended to combine some of the advantages of prototyping • More manageable process• Better system structure
Incremental Development Process
Validateincrement
Build systemincrement
Specify systemincrement
Design systemarchitecture
Define systemdeliverables
Systemcomplete?
Integrateincrement
Validatesystem
Deliver finalsystem
YES
NO
Throw-away Prototypes
Used to reduce requirements risk The prototype is developed from an initial
specification, delivered for experiment then discarded
The throw-away prototype must NOT be considered as a final system• Some system characteristics may have been left out
• There is no specification for long-term maintenance
• The system will be poorly structured and difficult to maintain
Throw-away Prototyping
Outlinerequirements
Developprototype
Evaluateprototype
Specifysystem
Developsoftware
Validatesystem
Deliveredsoftwaresystem
Reusablecomponents
Rapid Prototyping Techniques
Various techniques may be used for rapid development• Dynamic high-level language development
• Database programming
• Component and application assembly These techniques are often used together Visual programming is an inherent part of most
prototype development systems
Dynamic High-level Languages
Languages which include powerful data management facilities
Need a large run-time support system. Not normally used for large system development
Some languages offer excellent UI development facilities
Some languages have an integrated support environment whose facilities may be used in the prototype
Choice of Prototyping Language
What is the application domain of the problem? What user interaction is required? What support environment comes with the
language? Different parts of the system may be programmed
in different languages Example languages
• Java, Smalltalk, Lisp, Prolog, Perl, Tcl/TK
Database Programming Languages
Domain specific languages for business systems based around a database management system
Normally include a database query language, a screen generator, a report generator and a spreadsheet
May be integrated with a CASE toolset The language + environment is sometimes known as a “4GL” Cost-effective for small to medium sized business systems
DBprogramming
language
Interfacegenerator Spreadsheet
Reportgenerator
Database management system
Fourth-generation language
Prototyping with Reuse
Application level development• Entire application systems are integrated with the prototype so
that their functionality can be shared
• For example, if text preparation is required, a standard word processor can be used
Component level development• Components are mutually independent
• Individual components are integrated within a standard framework to implement the system
• Framework can be a scripting language or an integration platform.
Key points
A prototype can give end-users a concrete understanding of the system’s capabilities
Prototyping is used when rapid development is essential
Throw-away prototyping is used to understand the system requirements
In evolutionary prototyping, the system is developed by gradually adding features.
Guidelines
Rapid prototyping may require leaving out functionality or relaxing non-functional constraints
Prototyping techniques include the use of very high-level languages, database programming and prototype construction from reusable components
Prototyping is essential for parts of the system such as the user interface which cannot be effectively pre-specified
Users must be involved in prototype evaluation
Case History
Harbor Radar
CS 551 Senior Design
Project Overview
To primarily serve boaters in the Hudson River area with a 40 mile radius and inexpensive TV to display weather info, buoy data, and plotted locations
Interactive website• Accessible to everyone• Secure section where admin can control
information displayed with ability to plot coordinates and alter broadcast information
Difficult time writing requirements and setting scope
Requirements
Website Design-Easy to use, clean, intuitive and clearly display
maps Reliability
• High reliability requested by customer• Availability
» Ultimate goal of 24/7, however probably not doable. 20/7 has been suggested
Requirements (cont.)
Performance• Website will support 50 simultaneous users
» Reach for goal of 100• Television broadcast(s) place little load on the system• Response Time
» Average of .5s Constraints
• Television resolution will be an issue» Aim to be readable on a 9” screen
• Support both IE and Netscape, versions TBD
Map Module Screenshots
Larger View
Grid
Icons
Wrapper Module for TV Screens
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