Post on 25-Feb-2016
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Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 2
Outline
¨ Software Life Cycle Waterfall model and its problems
Pure Waterfall Model V-Model
Iterative process models Boehm’s Spiral Model
Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 3
Inherent Problems with Software Development¨ Requirements are complex
The client does not know the functional requirements in advance¨ Requirements may be changing
Technology enablers introduce new possibilities to deal with nonfunctional requirements
¨ Frequent changes are difficult to manage Identifying milestones and cost estimation is difficult
¨ There is more than one software system New system must be backward compatible with existing system
(“legacy system”) Phased development: Need to distinguish between the system
under development and already released systems¨ Let’s view these problems as the nonfunctional requirements
for a system that supports software development! This leads us to software life cycle modeling
Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 4
Definitions
¨ Software lifecycle modeling: Attempt to deal with complexity and change
¨ Software lifecycle: Set of activities and their relationships to each other to support the
development of a software system
¨ Software development methodology: A collection of techniques for building models - applied across the
software lifecycle
Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 5
Software Life Cycle
¨ Software construction goes through a progression of states
Development Post- Development
Pre- Development
Conception Childhood Adulthood Retirement
Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 6
Typical Software Lifecycle Questions
¨ Which activities should I select for the software project?
¨ What are the dependencies between activities? Does system design depend on analysis? Does
analysis depend on design?¨ How should I schedule the activities?
Should analysis precede design? Can analysis and design be done in parallel?Should they be done iteratively?
Copyright 2002 Bernd Brügge Software Engineering II, Lecture 3: Scheduling SS 2002 7
Identifying Software Development Activities For finding activities and dependencies we can use the
same modeling techniques when modeling a system such as creating scenarios, use case models, object identification, drawing class diagrams, activity diagrams
Questions to ask: What is the problem? What is the solution? What are the mechanisms that best implement the
solution? How is the solution constructed? Is the problem solved? Can the customer use the solution? How do we deal with changes that occur during the
development? Are enhancements needed?
Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 8
Possible Identification of Software Development Activities
Requirements Analysis What is the problem?
System Design What is the solution?
Program DesignWhat are the mechanismsthat best implement thesolution?
Program ImplementationHow is the solutionconstructed?
Testing Is the problem solved?
Delivery Can the customer use the solution?
Maintenance Are enhancements needed?
ProblemDomain
ImplementationDomain
Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 9
Software Development as Application Domain: A Use Case Model
<<include>><<include>>
<<include>>
Client End userDeveloperProject manager
Software development
System developmentProblem definition System operation
Administrator
Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 10
IEEE Std 1074: Standard for Software Lifecycle
IEEE Std 1074
Project Management
Pre-Development
Development Post-Development
Cross-Development
(Integral Processes)
> Project Initiation>Project Monitoring &Control> Software Quality Management
> Concept Exploration> System Allocation
> Requirements Analysis> Design> Implementation
> Installation> Operation & Support> Maintenance> Retirement
> V & V> Configuration Management> Documentation> Training
Process Group
Processes
Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 11
Processes, Activities, and Tasks¨ Process Group: Consists of Set of Processes¨ Process: Consists of Activities¨ Activity: Consists of sub activities and tasks
ProcessGroup
Process
Activity
Development
Design
Task
DesignDatabase
Make aPurchase
Recommendation
Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 12
Example
¨ The Design Process is part of Development¨ The Design Process consists of the following
Activities Perform Architectural Design Design Database (If Applicable) Design Interfaces Select or Develop Algorithms (If Applicable) Perform Detailed Design (= Object Design)
¨ The Design Database Activity has the following Tasks Review Relational Databases Review Object-Oriented Databases Make a Purchase recommendation ....
Copyright 2002 Bernd Brügge Software Engineering II, Lecture 3: Scheduling SS 2002 13
Many models have been proposed to deal with the problems of defining activities and associating them with each other
The first model proposed was the waterfall model [Royce 1970]
Life Cycle Modeling
Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 14
¨ Many models have been proposed to deal with the problems of defining activities and associating them with each other
¨ The waterfall model First described by Royce in 1970
¨ There seem to be at least as many versions as there are authorities - perhaps more
Life-Cycle Model: Variations on a Theme
Copyright 2002 Bernd Brügge Software Engineering II, Lecture 3: Scheduling SS 2002 15
RequirementsProcess
SystemAllocationProcess
ConceptExplorationProcess
DesignProcess
ImplementationProcess
InstallationProcess
Operation &Support Process
Verification& Validation
Process
The Waterfall Model of the Software Life Cycle
adapted from [Royce 1970]
Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 16
Problems with Waterfall Model
¨ Managers love waterfall models: Nice milestones No need to look back (linear system), one activity at a time Easy to check progress : 90% coded, 20% tested
¨ V-Model ¨ Software development is iterative
During design problems with requirements are identified During coding, design and requirement problems are found During testing, coding, design& requirement errors are found => Spiral Model
Copyright 2002 Bernd Brügge Software Engineering II, Lecture 3: Scheduling SS 2002 17
From the Waterfall Model to the V Model
System Design
Requirements
Analysis
Requirements
Engineering
Object Design
Integration Testing
System Testing
Unit Testing
Implementation
SystemTesting
Unit Testing
Integration Testing
Acceptance
Copyright 2002 Bernd Brügge Software Engineering II, Lecture 3: Scheduling SS 2002 18
Activity Diagram of a V ModelSystem
RequirementsAnalysis
Implementation
PreliminaryDesign
DetailedDesign
SoftwareRequirementsElicitation
Operation
ClientAcceptance
RequirementsAnalysis
UnitTest
SystemIntegration
& Test
ComponentIntegration
& Test
precedes
Is validated by
Copyright 2002 Bernd Brügge Software Engineering II, Lecture 3: Scheduling SS 2002 19
Properties of Waterfall -based Models Managers love waterfall models:
Nice milestones No need to look back (linear system) Always one activity at a time Easy to check progress during development: 90%
coded, 20% tested However, software development is nonlinear
While a design is being developed, problems with requirements are identified
While a program is being coded, design and requirement problems are found
While a program is tested, coding errors, design errors and requirement errors are found
Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 20
¨ The spiral model proposed by Boehm is an iterative model with the following activities Determine objectives and constraints Evaluate Alternatives Identify risks Resolve risks by assigning priorities to risks Develop a series of prototypes for the identified risks starting with
the highest risk. Use a waterfall model for each prototype development (“cycle”) If a risk has successfully been resolved, evaluate the results of the
“cycle” and plan the next round If a certain risk cannot be resolved, terminate the project
immediately
Spiral Model (Boehm) Deals with Iteration
Copyright 2002 Bernd Brügge Software Engineering II, Lecture 3: Scheduling SS 2002 21
Spiral ModelDetermine objectives,alternatives, & constraints
Evaluate alternatives,identify & resolve risks
Develop & ver ifynext level productPlan next phase
Requirements
Development
Integration
plan
plan
plan
Requirements
Design
validation
validation
Software SystemProduct
Riskanalysis
Riskanalysis
Prototype1Prototype2
Prototype3
Riskanalysis
Concept ofoperation
RequirementsDesign
Code
Unit Test
Integration & TestAcceptance
DetailedDesign
P1
P2
Test
Project P1
Project P2
Copyright 2002 Bernd Brügge Software Engineering II, Lecture 3: Scheduling SS 2002 22
Types of Prototypes Illustrative Prototype (Revolutionary Prototyping)
Develop the user interface with a set of storyboards Implement them on a napkin or with a user
interface builder (Visual C++, ....) Good for first dialog with client
Functional Prototype (Evolutionary Prototyping) Implement and deliver an operational system with
minimum functionality Then add more functionality Order identified by risk
Exploratory Prototype ("Hacking") Implement part of the system to learn more about
the requirements.
Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 23
Process Maturity
¨ A software development process is mature if the development activities are well defined and if management has some control over the quality, budget and
schedule of the project¨ Process maturity is described with
a set of maturity levels and the associated measurements (metrics) to manage the process
¨ Assumption: With increasing maturity the risk of project failure decreases
Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 24
Capability maturity levels
1. Initial Level also called ad hoc or chaotic
2. Repeatable Level Process depends on individuals ("champions")
3. Defined Level Process is institutionalized (sanctioned by management)
4. Managed Level Activities are measured and provide feedback for resource
allocation (process itself does not change)5. Optimizing Level
Process allows feedback of information to change process itself
Copyright 2002 Bernd Brügge Software Engineering II, Lecture 3: Scheduling SS 2002 25
Maturity Level 1: Chaotic Process
Ad hoc approach to software development activities No problem statement or requirements specification Output is expected
but nobody knows how to get there in a deterministic fashion
Similar projects may vary widely in productivity "when we did it last year we got it done"
Level 1 Metrics: Rate of Productivity (Baseline comparisons, Collection of data is difficult)
Product size (LOC, number of functions, etc)
Staff effort (“Man-years”, person-months)
Recommendation: Level 1 managers & developers should not concentrate on metrics and their meanings,
They should first attempt to adopt a process model (waterfall, spiral model, saw-tooth, macro/micro process lifecycle, unified process)
Copyright 2002 Bernd Brügge Software Engineering II, Lecture 3: Scheduling SS 2002 26
Maturity Level 2: Repeatable Process
Inputs and outputs are defined Input: Problem statement or requirements specification Output: Source code
Process itself is a black box ( activities within process are not known)
No intermediate products are visible No intermediate deliverables
Process is repeatable due to some individuals who know how to do it
"Champion"
Level 2 Metrics: Software size: Lines of
code, Function points, classes or method counts
Personnel efforts: person-months
Technical expertise Experience with
application domain Design experience Tools & Method
experience Employee turnover
within project
Copyright 2002 Bernd Brügge Software Engineering II, Lecture 3: Scheduling SS 2002 27
Maturity Level 3: Defined Process
Activities of software development process are well defined with clear entry and exit conditions.
Intermediate products of development are well defined and visible
Level 3 Metrics (in addition to metrics from lower maturity levels):
Requirements complexity: Number of classes, methods, interfaces
Design complexity: Number of subsystems, concurrency, platforms
Implementation complexity: Number of code modules, code complexity
Testing complexity: Number of paths to test, number of class interfaces to test
Thoroughness of Testing:
Requirements defects discovered
Design defects discovered
Code defects discovered
Failure density per unit (subsystem, code module, class
Copyright 2002 Bernd Brügge Software Engineering II, Lecture 3: Scheduling SS 2002 28
Maturity Level 4: Managed Process Uses information from early
project activities to set priorities for later project activities (intra-project feedback)
The feedback determines how and in what order resources are deployed
Effects of changes in one activity can be tracked in the others
Level 4 Metrics: Number of iterations per
activity Code reuse: Amount of
producer reuse (time designated for reuse for future projects?)
Amount of component reuse (reuse of components from other projects and components)
Defect identification: How and when (which
review) are defects discovered?
Defect density: When is testing
complete? Configuration
management: Is it used during the
development process? (Has impact on tractability of changes).
Module completion time: Rate at which modules
are completed (Slow rate indicates that the process needs to be improved).
Copyright 2002 Bernd Brügge Software Engineering II, Lecture 3: Scheduling SS 2002 29
Maturity Level 5: Optimizing Process
Measures from software development activities are used to change and improve the current process
This change can affect both the organization and the project: The organization might change its management
scheme A project may change its process model before
completion
Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 30
Summary
¨ Software life cycle The development process is broken into individual pieces called
software development activities¨ No good model for modeling the process (black art)
Existing models are an inexact representation of reality Nothing really convincing is available today
¨ Software development standards IEEE 1074 Standards help, but must be taken with a grain of salt The standard allows the lifecycle to be tailored
¨ Capability Maturity Model.