introduction to software process cen 5016 software engineering © dr. david a. workman school of ee...

Introductionto

Software Process

CEN 5016

Software Engineering

© Dr. David A. Workman

School of EE and Computer Science

January 9, 2007

January 9, 2007 (c) Dr. David A. Workman 2

Software Engineering

DEFINITION [Barry Boehm’76].

The practical application of scientific knowledge in the design and construction of computer programs and the associated documentation required to develop, operate, and maintain them.

– Practical Applications

– Scientific Knowledge

– Design and Construction

– Computer Programs and Documentation

– Develop, operate, and maintain

DEFINITION [IEEE 1993]1. The application of a systematic, disciplined, quantifiable approach to the

development, operation, and maintenance of software; that is, the application of engineering to software.

2. The study of approaches relevant to 1.


Computer Science

DEFINITION

Computer Science is concerned with the scientific study and description of algorithms, programs, the devices that interpret them, and the phenomena surrounding their creation and usage.

Software Engineering focuses on the application of this scientific knowledge to achieve stated technical, economic, and social goals.

[Peter Freeman’80]


Life Cycle vs. Development Cycle

“Cradle” “Grave”

Needand ConceptFormation

Obsolescenceand De-Commission

SystemsEngineering

SoftwareRequirements

Elicitation

SoftwareRequirementsElaboration

Software Specificationand Project Planning

SoftwareDesign

Code &Unit Testing

ComponentIntegration

andSystem Test

DeliveryInstallation& Training

Operationand

Maintenance

Software Development Cycle


Summary of the Software LifecycleDefinition

The complete history of a software system from concept formation through decommission broken down into the following “maturation” phases:

– Conception– System Requirements elicitation and definition– System Architecture Development– Software Requirements elicitation and definition– Software Requirements elaboration and specification– Software Project Planning– Design

• Architectural Design• Detailed Design

– Implementation• Coding• Unit Testing

– Integration• Subsystem testing• System testing (acceptance testing)

– Operation & Maintenance• Corrective : removing bugs ( 17.5% )• Enhancement: improving exiting capability = perfective ( 60.5%) + adaptive ( 18% )• Reengineering (includes adaptive and perfective maintenance)

– Retirement

Construction

Systems Engineering


Development Cycle Costs

Integration = 24%

Unit Testing = 21%

Coding = 15%

Design = 19%

Specification = 15%

Requirements = 6%

(Schach - Classical and Object-Oriented Software Engineering)


Process Models

• Definition

Process models are “algorithms for developing software.” Software process is the execution of a process model.Data = development artifacts; Processors = people; Algorithms = methods + tools

• Water Fall Model (Winston Royce ’70)

– First formal software development method (1950-70).

– Each development phase was completed before the next could begin.

– Documents produced as the output of one phase become inputs to the next phase.

– Did not allow for changing requirements. Frequently, the user was not happy with the delivered system.

Phases:• System Engineering

• Software Requirements Analysis

• Software Design (Architectural & Detailed)

• Code and Unit Testing

• Integration

• Installation & Maintenance


Water Fall Model

Features & Contributions– Author: Winston Royce 1970

– First formal software development method (1950-70).

– Encouraged specification of what the system is supposed to do before building it.

– Encouraged planning and management monitoring and control.

– Each development phase was completed before the next could begin.

– Documents produced as the output of one phase become inputs to the next phase.These documents provided a basis for verification and validation.

– Did not allow for changing requirements. Frequently, the user was not happy with the delivered system.

SystemRequirements

SoftwareRequirements Architectural

DesignDetailedDesign

Code & UnitTest

Integration& Test

Installation& Maintenance

rework

rework

rework

rework

rework


Water Fall Model

1. System Requirements: The system concept is defined, customer and client requirements are captured, hardware and software components defined and mapped.

2. Software Requirements: a formal (complete, precise, consistent, and unambiguous) description of “what” each software component must do is prepared by the developer and reviewed by the customer (software specification document); a software project plan is produced at the end of this phase.

3. Design phase: The specification is elaborated in two steps that define “how” the product will work: Architectural Design breaks down the whole system into component parts (modules) and the interactions between them (interfaces); Detailed Design involves elaborating the design of individual components by specifying data structures and algorithms.

4. Code & Unit: Software module designs are translated to code and then unit tested.5. Integration & Test: Software modules are integrated into larger functional

aggregates (subsystems) and tested in the operational environment. The final step tests the complete system (acceptance testing or validation – customer agrees that the system meets the specification).

6. Installation & Maintenance: The completed system is installed in the operational environment and maintained (error correction and enhancement) for the remainder of the system lifetime.


Water Fall Model

RequirementsSpecification

Design

UnitTest

Code

Integration& Test

SystemAcceptance

Tests

Errors DetectedErrors Introduced

Ref: The Impact of Prototyping on Software System Engineering, by Hassan Gomaa, George Mason University, IEEE System and Software Requirements Engineering, 1990.


Prototyping

• Prototyping

The rapid and (relatively) inexpensive development of an operating model of the desired system (or a subset) developed only for the purpose of defining or elaborating requirements, and/or resolving unknown performance issues before a full commitment of resources is made to produce the final system.

• Benefits– Water Fall models limit the amount of iteration among phases – a key feature of

prototyping is iterating rapidly through early phases of development.

– Water Fall models tend to produce a working system very late in the development cycle – thus major problems may go undetected until the system is almost complete. Prototyping focuses on identifying major technical problems as early as possible.

– System requirements cannot be properly validated without a working version – prototyping focuses on understanding and elaborating requirements through demonstration.

Ref: The Impact of Prototyping on Software System Engineering, by Hassan Gomaa, George Mason University, IEEE System and Software Requirements Engineering, 1990.


Prototyping

Requirements for a Prototype1. It must be an actual working system with which one can experiment and from

which lessons can be learned to revise the requirements specification.

2. It must be comparatively cheap to develop – approximately 10% of the total estimated cost of the complete system.

3. Must be developed quickly so that it may be evaluated early in the development cycle; it should be used to collect early feedback from system users.

Phases of Development1. Preliminary analysis and specification of user requirements. (understand user's

problem)

2. Design and implementation of a prototype. (emphasize user interface, small development team, development language, use prototyping development tools)

3. Exercise the prototype. (preliminary user training, user feedback)

4. Iterative refinement of the prototype.

5. Refinement of the requirements specification.

6. Design and implementation of the production system.See Notes


Prototyping• Throwaway Prototypes are constructed as part of the problem

understanding or analysis activity. Their purpose is to gain a deeper understanding of the problem and its feasible solutions. It is a learning device never intended for use - it is “thrown away” after it has served its purpose.

– Because the prototype will be discarded, the time and effort spent on satisfying non-functional requirements and formal documentation can almost be eliminated. This reduces development time.

– This approach should focus on understanding of requirements from the user's perspective and to obtain early user feedback.

• Evolutionary Prototypes are constructed to satisfy a subset of the system requirements - as refinements are made or layers of functionality are added, they “evolve” into the final system.

– Because each increment or prototype version is to be of production quality, non-functional requirements must be considered and some formal documentation must be part of the prototyping process.

– The incremental nature of evolutionary prototyping ensures that a useful version of the system is produced earlier that water fall methods.

See Notes


Reengineering Process Model

LegacySystem

ProposedNew

Capability

TargetSystem

EstablishBaseline

LegacyBaseline

ExtractRequirements

RequirementsAnalysis

Modify &EnhanceDesign

Reuse &ModifyLegacyUnits

Construct & Testnew Units

Re-TestLegacy Units

ProduceNew Test

Plan

ExtractDesign

LegacyRequirements

NewRequirements

ModifiedRequirements

LegacyDesign

DesignChanges

TestChanges

NewDesign

NewDesign

Re-testProcedures

New Unit testProcedures

Integration testProcedures

Testednew Units

TestedLegacy Units

Integrate & TestAll

Units

IdentifiedLegacy Unitsfor Reuse & Modification

Set of Test-readyLegacy Units

Legacy Test Procedures,Test Data & Results

ReuseLibraries

Identifiyoff-the-shelf

UnitsFor reuseWithout

modification

Off-the-shelf Unitsready for Integration


Spiral Model

A cyclic approach to software development marked by four basic stages that are repeated on each cycle until the target system is delivered. A risk-driven meta model.

Developed by Barry Boehm, “A Spiral Model of Software Development and Enhancement”, IEEE Computer, Vol 21, No 5, May 1988.

Stage 1: Identify objectives, alternative solutions, and constraints for the part of the system currently under consideration.

Stage 2: Evaluate alternatives and identify associated risks using prototyping and simulation.

Stage 3: Develop and verify the next system increment.

Stage 4: Review outcome of earlier stages and plan the next cycle.


Spiral Model

2: Evaluate alternatives and their risks

1: Determine objectives, alternative solutions, & constraints.

4: Review outcome andPlan next cycle.

3: Develop, verify next

system increment.

risk analysis

prototyping

Design

Implementation

Planning

Review Test

Acceptance &

Installation

See Notes


Measurement and Control

DevelopmentActivity or Procedure

QualityReview

Progress & QualityAssessment

Process Change

Directives

(Project Mangement)

Product Change

Directives

Quality

Products

(and specification for next Activity)

Raw

Products

Product

Specifications

Effort and Size

Metrics Quality Metrics

Progress & Quality

Data

MetricsRepository

Nominal Process Flow or Execution

Process Quality Assessment and Control Product Quality Assessment and Control

See Notes

Unified Software ProcessSoftware Phases & Artifacts


Overview of USP

RequirementsElaboaration

(OO-Analysis)

RequirementsElaboaration

(OO-Analysis)

Object-OrientedDesign

Object-OrientedDesign

Object-OrientedImplementation(Programming)

Object-OrientedImplementation(Programming)

Problem Statement& User NeedsUse Case

Model

The process of defining and modeling the Problem Space

The process of defining and modeling the Solution Space

Design & DeploymentModels

Code in anOOPL (Ada95)(C++)(Java)ComponentModel

Mapping design to Implementation Space

RequirementsElicitation

(Definition)

RequirementsElicitation

(Definition)

Analysis Model


Overview of USP

• Inception (focus on “Feasibility”)Develop a vision of the end product and prepare a business case. Answers the

questions:• What is the system boundary? Begin to identify interfaces with systems outside the

boundary. • What is the system going to do? What are the major classes of users? (Develop

Initial Use Case Model )( Identify and describe only a small % of use cases )• What is a possible system architecture? ( Identify most critical subsystems )• What is the project plan? What will the system cost? ( Identify critical risks )

(Develop a Project Management Plan)• Demonstrate feasibility by building a prototype.

• Elaboration• Construction• Transition

Inception Elaboration Construction Transition

Birth Death

Itera-tion

Itera-tion

Itera-tion

Itera-tion

Itera-tion

Itera-tion

Itera-tion

Itera-tion… …

Itera-tion

Itera-tion


Overview of USP

• Inception

• Elaboration ( focus on “Do-Ability” )(Architecture + high-fidelity cost est.)– Develop detailed use cases (80% of use cases).

– Develop a stable architectural view of the system using the Analysis Model, Design Model, Implementation Model, and Deployment Model.

– Create a baseline system specification (SRS).

– Produce the Software Development Plan (SDP) which describes the next phase.

• Construction

• Transition


Birth Death

Itera-tion

Itera-tion

Itera-tion

Itera-tion

Itera-tion

Itera-tion

Itera-tion

Itera-tion… …

Itera-tion

Itera-tion

Arch. Design Detailed Design


Overview of USP

• Inception• Elaboration• Construction (focus on building an operational capability)

Build the system (usually in increments defined by releases ). Each release encapsulates defined use cases. Releases are ordered by priority determined by customer needs and project risks.

• Transition (focus on producing a formal release )Product (release) enters beta testing and then distribution. This phase involves

manufacturing, training, and providing customer support infrastructure.Transition ends with maintenance: corrective, adaptive, perfective.


Birth Death

Itera-tion

Itera-tion

Itera-tion

Itera-tion

Itera-tion

Itera-tion

Itera-tion

Itera-tion… …

Itera-tion

Itera-tion


Overview of USPUSDP Models

test1OK

test2OKUse Case Model

Analysis Model

Design Model

Test Model

Implementation Model Deployment

Model

implementedby

realizedby

specifiedby

distributedby

verifiedby


Overview of USP

Core Work Flows

Elicitation

Analysis

Design

Implementation

Test


Distribution of Core Activities Across Phases

Use Case Modeling

© Dr. David A. Workman

School of EE and Computer Science

University of Central Florida

September 18, 2002


Requirements Capture

• InputClient approaches Developer with a problem and or product concept. This may be

expressed verbally or in the form of a document (Statement of Work (SOW)) (Request for Proposal (RFP))

• ActivitiesDeveloper interacts with Client and Users to elicit product requirements. This

involves face-to-face meetings and possibly the exchange of technical documents. The Developer must determine as completely and precisely as possible the following information:

– cost and time constraints – target system platform and operational environment– user groups– functional capabilities– non-functional constraints: quality and performance– Client and User's needs (as opposed to "wants")

• OutputsA complete understanding of the problem the Client and Users need to have solved.Client should be in agreement with the Developer’s assessment of the problem. This

shared view of the system is captured in the form of a UML Use Case Model.


Use Case Model• Definitions1

A Use Case is a sequence of actions that the system performs to offer some results of value to a User.

– Use cases drive the whole development process. “They offer a systematic and intuitive means of capturing functional requirements from the user’s perspective.”

– A system has many types of users. Each type of user is define by an actor. Actors may be people or external systems. Actors interact with the product via one or more Use Cases. An actor role is defined by a particular set of use cases performed by that actor to accomplish a particular goal or objective.

– “All actors and uses cases make up a Use Case Model.”

– A good collection of use cases is central to understanding what your users want. Use Cases also present a good vehicle for project planning, because they control iterative development, … it gives regular feedback to users about where the software is going.

– Use cases provide the basis of communication between the client and the developers in planning the project.

1The Unified Software Development Process, by Rumbaugh, Jacobson, and Booch, Addison-Wesley, 1999, 0-201-57169-2.


Use Case Model

• Definition2 (Fowler)A Use Case captures a typical interaction between a user and a computer system.

– A use case captures some user-visible function.

– A use case may be small or large.

– A use case achieves a discrete objective for the user.

In its simplest usage, you capture a use case by talking to typical users and discussing the various things they might want to do with the system. Take each discrete task or action they want to do, give it a name, and write up a short description.

During the Elaboration phase, this is all you need to do to get started.

2UML Distilled, by Scott & Fowler


Use Case Model Outline• Title (System Name, Author Name, Assignment, Course, Pub. Date)

– TOC– List of Figures (optional for small documents)

1. System Summary– Overview of System Purpose and Context– Business Case ( business need and how this system will address this need )– System Operation

• Use Case Diagram• Supporting Narrative (explains diagram: operational flow, actor roles )

– System Interfaces ( External Interfaces with Actors )

2. Use Case Specifications1. Purpose ( function from user’s perspective )

• Collaboration diagram (flow of interactions between actors and interface objects )• Narrative summary of use case purpose or function

2. Precondition (system states & triggering events )3. Flow of Events (nominal flow of interaction events between actor and interface objects)4. Alternative Paths (error processing flows; special case flows )5. Post Condition (system states & completion events )6. Special Requirements (non-functional : performance and quality )

3. Requirements Traceability4. Glossary


Requirements Elicitation Work Flow

SystemAnalyst

SystemArchitect

Use CaseSpecialist

User InterfaceDesigner

Find Actors& Use Cases

StructureUse Case

Model

PrioritizeUse Cases

DetailUse Cases

PrototypeUser Interface


Requirements Elaboration

• Purpose"To achieve a more precise understanding of requirements and to achieve a description of

requirements that is easy to maintain and that helps give structure to the whole system - including the architecture."

• Inputs– Outputs from Requirements Elicitation ( Use Case Model ).– Technical documents or expertise relevant to problem domain, in general, and to the Client's

problem, in particular.– Legacy System (optional)

• ActivitiesRefine requirements by eliminating inconsistencies and ambiguities. Formalize requirements by

preparing a System/Software Requirements Specification. Develop an initial Software Development Plan.

• Outputs– System/Software Requirements Specification (SRS)

• UML Use Case Model and Scenarios• UML Class Model • UML Collaboration Model • UML Sequence Diagrams• Problem Glossary• Other info.

– Software Development Plan (SDP)


Software Requirements Specification (SRS)1

• Title• TOC

1. Introduction1.1 Purpose

1.2 Scope

1.3 Definitions, Acronyms, and Abbreviations

1.4 References

1.5 Overview

2. Overall Description2.1 Product Perspective

2.2 Product Functions

2.3 User Characteristics

2.4 Constraints

2.5 Assumptions and Dependencies

3.0 Specific Requirements… next slide

1 IEEE Std 830-1998


Software Requirements Specification (SRS)

3.0 Specific Requirements

3.1 External Interfaces

3.2 Functions

3.3 Performance Requirements

3.4 Logical Database Requirements

3.5 Design Constraints

3.6 Software System Quality Attributes

3.7 Object Oriented Models

3.7.1 Analysis Class Model

3.7.2 Analysis Collaboration Model

3.8 Additional Comments

• Index

• Appendices


Software Development Plan (SDP)2

• Front Matter (Title, Toc, Lof, Lot)

1. Overview1.1 Project Summary

1.2 Evolution of Plan

2. References

3. Definitions

4. Project Organization

5. Managerial Process Plans5.1 Start-up Plan

5.2 Work Plan

5.3 Control Plan

5.4 Risk Management Plan

5.5 Closeout Plan

6. Technical Process Plan

7. Supporting Plans

2 IEEE Std 1058-1998


Requirements Elicitation vs Elaboration (USP)

Use-case Model Analysis Model Described using the language of the customer.

Described using the language of the developer.

External view of the system. Internal view of the system.

Structured by Use cases; gives structure to external view

Structured by sterotypical classes and packages; gives structure to internal view

Used primarily as a contract between client and developer as to what the system should do.

Used primarily by developers to understand how the system should be shaped; that is, designed and implemented.

May contain redundancies and inconsistencies among requirements

Should be complete, precise, consistent, and testable.

Captures functionality of the system including architecturally significant functionality.

Outlines how to realize functionality within the system; works as the first cut at design.

Defines use cases further analyzed in the analysis model.

Defines Use-case realizations, each one representing the analysis of a use case from the Use Case model.


Design (USP)

• PurposeThe system is shaped to accommodate all functional and non-functional

requirements. It contributes to a sound and stable architecture and creates a blueprint for the implementation model.

– Acquire an in-depth understanding of non-functional requirements and constraints related to: programming languages, component reuse, operating systems, distribution topology, network and database technologies, user-interface technology, etc.

– Define and harden the boundaries between subsystems.

• Artifacts– Design Model

An object model that describes the physical realization of use cases by focusing on how functional and non-functional requirements, together with other constraints related to the implementation environment, impact the system architecture and structure.

• Design classes

• Use-case realizations (design)

• Detailed Interfaces


Design (USP)

• Artifacts– Architecture Description

A view of the design model focusing on the following architecturally significant artifacts:

• Subsystems, interfaces, and their dependencies

• Key classes that trace to key analysis and active classes

• Key use case realizations that are functionally critical and need to be developed early in the lifecycle. Ones that have coverage across subsystems are particularly important.

– Deployment ModelAn object model that describes the physical distribution of the system in terms of how

functionality is distributed among computational nodes. An essential input to the activities in design and implementation. It is a manifestation of the mapping between software architecture and system architecture.

• Nodes that denote computational resources

• Node processes and corresponding functional allocation

• Node relationships and their types (internet, shared memory, ATM link, etc.)

• Network topology(ies)


Analysis vs Design (USP)

Analysis Model Design Model A conceptual model, because it is an abstraction of the system and avoids implementation issues.

A physical model, because it is a blueprint for implementation.

Design-generic (applicable to several possible designs).

Specific for an implementation.

Based on three stereotyped classes that are conceptual in nature: Entity, Boundary, and Control.

Any number of physical class stereotypes and modules that may be implementation language dependent.

Less formal. More formal.

Less effort to develop (1:5 ratio) More effort to develop

Few layers Many layers

Dynamic, but not much focus on sequence.

Dynamic with much more emphasis on sequence, concurrency, and distribution.

Outlines the design and architecture of the system.

Manifests or realizes the design (an instantiation of the Analysis Model).

May not be maintained throughout the lifecycle.

Should be maintained throughout the lifecycle.

Defines a structure that is an essential input to shaping the system including the Design Model.

Defines the structure of the system wrt both functional and non-functional requirements.


Implementation (USP)

• PurposeTo translate the design into machine-readable and executable form. Specifically to:

– Plan system integrations required in each implementation increment or iteration

– Distribute the system by mapping executable components to nodes in the deployment model.

– Implement design classes and subsystems found in the Design Model.

– Unit test the components, and integrate them by compiling and linking them together into one or more executables, before they are sent to integration and system tests.

• Artifacts– Implementation Model

• Components: <executable>, <file>, <library>, <Dbtable>, <document>

• Interfaces

• Implementation subsystems

– Components

– Implementation Subsystems

– Interfaces

– Build Plan


Integration & Test (USP)

• PurposeTo verify the result of each build and to validate the complete system via acceptance

tests.

– Plan tests required in each iteration, including integration and system tests. Integration tests are required after each build, while system tests are done as part of client acceptance and system delivery.

– Design and implement test plans by creating test cases. Test cases specify what to test and define procedures and programs for conducting test exercises.

– Perform various test cases to capture and verify test results. Defects are formally captured, tracked and removed before delivery.


Integration & Test (USP)• Artifacts

– Test PlanDescribes testing strategies, resources, and schedule for each build and for the system.

– Test Model• Test Case

• Test Component

• Test Procedure

– Test CasesDesigned to verify certain requirements and use cases, or use case scenarios.

Demonstrates that pre- and post-conditions of use cases are satisfied. Predicts or describes expected component output and behavior.

– Test ComponentsThe implementation artifacts to be tested.

– Test ProceduresSpecifies how to perform one or several test cases. Test programs (or "harnesses")(or

"benches") and shell scripts may have to be executed as part of a test procedure.

– Test EvaluationsCapture results of test cases; declares whether or not test case was successful; generates

defect or anomaly reports for tracking.

– Defect or Anomaly Reports


IEEE Std (829) for Software Testing

• Test PlanTo prescribe the scope, approach, resources, and schedule of testing activities. To

identify items to be tested, the features to be tested, the testing tasks to be performed, the personnel responsible for each task, and the risks associated with the plan.

• Test Design Spec

• Test Case Spec

• Test Procedure Spec

• Test Item Transmittal Report

• Test Log

• Test Incident Report

• Test Summary Report

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