System Engineering

Chapter 6 based on Software Engineering: A Practitioner’s Approach, 6/e

copyright © 1996, 2001, 2005

R.S. Pressman & Associates, Inc.

For University Use Only

May be reproduced ONLY for student use at the university level when used in conjunction with

Software Engineering: A Practitioner's Approach.

Any other reproduction or use is expressly prohibited.

1

Waterfall model 1

[aka Royce1970]

Systems Engineering Software Req. Analysis Project Planning Operation/Maintenance Design Implementation Testing/Verification Release 2

System Engineering



Elements of a computer-based system

     

Software Hardware People

Database Documentation Procedures



Systems

 A hierarchy of macro-elements 3

Business Process (Re-)Engineering



to identify how

information systems

can best meet the

strategic goals

of an

enterprise

,

using an integrated set of procedures, methods, and tools, given a set of business rules and constraints.



focuses first on the

enterprise

and then on the

business

area



creates

enterprise

models,

data

models and

process

models

(processes/services and interrelationships of processes and data) 

creates a framework for better information management, distribution, and control

4

System Architectures

 Three different architectures must be analyzed and designed within the context of business objectives and goals: 

data architecture

provides a framework for the information needs of a business or business function (e.g., incident location, patient status, ambulance location, drivers’ lunch hours and break, hospital locations, etc.) 

application architecture

encompasses those elements of a system that transform objects within the data architecture for some business purpose (e.g., determine ambulance availability, determine hospital availability, etc.) 

technology infrastructure

provides the foundation for the data and application architectures (e.g., communication lines, computer platforms, etc.) 5

System Modeling with UML

  

Deployment diagrams

 Each 3-D box depicts a hardware element that is part of the physical architecture of the system

Activity diagrams

 Represent procedural aspects of a system element

Class diagrams

 Represent system level elements in terms of the data that describe the element and the operations that manipulate the data 6

Skip – Self Reading Possibly One Lecture on UML

7

Conveyor Line Sorting System (CLSS)

CLSS must be developed such that boxes moving along a conveyor line will be identified and sorted into one of six bins at the end of the line. The boxes will pass by a sorting station where they will be identified. Based on an identification number printed on the side of the box and a bar code, the boxes will be shunted into the appropriate bins. Boxes pass in random order and are evenly spaced. The line is moving slowly.

A desk-top computer located at the sorting station executes all CLSS software, interacts with the bar-code reader to read part numbers on each box, interacts with the conveyor line monitoring equipment to acquire conveyor line speed, stores all part numbers sorted, interacts with a sorting station operator to produce a variety of reports and diagnostics, sends control signals to the shunting hardware to sort the boxes, and communicates with a central factory automation system.

8

Deployment Diagram

CLSS processor Sort ing subsyst em Operat or display Sensor dat a acquisit ion subsyst em shunt cont roller Conveyor Pulse t ach Bar code reader Shunt act uat or 9

Activity Diagram

st a rt c o n v e y o r l i n e re a d b a r c o d e g e t c o n v e y o r sp e e d v alid bar c ode inv alid bar c ode d e t e r m i n e b i n l o c a t i o n se t f o r re j e c t b i n g e t sh u n t st a t u s se n d sh u n t c o n t ro l d a t a re a d b a r c o d e g e t c o n v e y o r st a t u s p ro d u c e re p o rt e n t ry c onv ey or s t opped c onv ey or in m ot ion 10

Box barcode forwardSpeed conveyorLocat ion height widt h dept h weight cont ent s readBarcode( ) updat eSpeed ( ) readSpeed( ) updat eLocat ion( ) readLocat ion( ) get Dimensions( ) get Weight( ) checkCont ent s( )

Class Diagram

class name at t ribut es not e use of capit al let t er f or mult i-word at t ribut e names operat ions ( parent heses at end of name indicat e t he list of at t ribut es t hat t he operat ion requires) 11

Requirements Engineering

Chapter 7 based on Software Engineering: A Practitioner’s Approach, 6/e

copyright © 1996, 2001, 2005

R.S. Pressman & Associates, Inc.

For University Use Only

May be reproduced ONLY for student use at the university level when used in conjunction with

Software Engineering: A Practitioner's Approach.

Any other reproduction or use is expressly prohibited.

12



Requirements Engineering Process: A Basic Framework [Loucopolos] Many variations and extensions 3 fundamental activities: understand, (formally) describe, attain an agreement on, the problem

User reqs User User feedback    Elicitation knowledge For more knowledge Specification Req. models Val. result Validation Domain knowledge Problem Domain Domain knowledge (domain experts, laws, standards, policies, documents, etc.)

Elicitation: determine what ’ s really needed, why needed, whom to talk to Specification: produce a (formal) RS model: translate "vague" into "concrete", etc. make various decisions on what & how Validation: assure that the RS model satisfies the users ’ needs

13

Requirements Engineering

   Elicitation - Inception —ask a set of questions that establish …  (basic) understanding of the problem    the people who want a solution the nature of the solution that is desired, and the effectiveness of preliminary communication and collaboration between the customer and the developer Specification — can be any one (or more) of the following:    A written document A set of models - A formal mathematical?

A collection of user scenarios (use-cases)  A prototype Validation — a review mechanism that looks for      errors in content or interpretation areas where clarification may be required missing information inconsistencies (a major problem when large products or systems are engineered) conflicting or unrealistic (unachievable) requirements. 14

Eliciting Requirements - Inception

   Identify (key)

stakeholders

  These are the people who will be involved in the negotiation “who else do you think I should talk to?” Recognize multiple points of

view

Work toward

collaboration

 The first

questions

    Who is behind the request for this work?

Who will use the solution?

What will be the (economic) benefit of a successful solution Is there another source for the solution that you need?

15

Eliciting Requirements

    

meetings

are conducted and attended by both software engineers and customers rules for preparation and participation are established an

agenda

is suggested a "

facilitator

" (can be a customer, a developer, or an outsider) controls the meeting a "

definition mechanism

" (can be work sheets, flip charts, or wall stickers or an electronic bulletin board, chat room or virtual forum) is used  the goal is  to identify the problem    propose elements of the solution negotiate different approaches, and specify a preliminary set of solution requirements 16

Elicitation Work Products

      a statement of

need, scope

, and

feasibility

.

a list of customers, users, and other

stakeholders

participated in requirements elicitation who a description of the system’s technical

environment (cf. enterprise model in system engineering)

.

a list of

requirements

(preferably organized by function) and the

domain constraints

that apply to each.

a set of

usage scenarios

that provide insight into the use of the system or product under different operating conditions.

any

prototypes

developed to better define requirements

.

17

Building the Analysis Model



Elements of the analysis model

 Scenario-based elements   Functional —processing narratives for software functions Use-case —descriptions of the interaction between an “actor” and the system    Class-based elements  Implied by scenarios Behavioral elements  State diagram Flow-oriented elements  Data flow diagram 18

Skip – Self Reading Possibly One Lecture on UML

19

Use-Cases

  A collection of

user scenarios

that describe the thread of usage of a system Each scenario is described from the point-of view of an “

actor

”—a person or device that interacts with the software in some way  Each scenario answers the following questions:   Who is the primary actor, the secondary actor (s)?

What are the actor’s goals?

        What preconditions should exist before the story begins?

What main tasks or

functions

are performed by the actor?

What extensions might be considered as the story is described?

What variations in the actor’s interaction are possible?

What system information will the actor acquire, produce, or change?

Will the actor have to inform the system about changes in the external environment?

What information does the actor desire from the system?

Does the actor wish to be informed about unexpected changes?

20

Use-Case Diagram

Ar ms/ disar ms syst em sensor s homeow ner Accesses syst em via Int er net Responds t o alar m event syst em administ r at or Encount er s an er r or condit ion Reconf igur es sensor s and r elat ed syst em f eat ur es 21

Class Diagram

From the

SafeHome

system …

Sensor

name/id type location area characteristic s identify() enable() disable() rec onfigure () 22

State Diagram

t ur n copier “on“ Init ializat ion syst em st at us= “not ready” display msg = “please wait ” display st at us = blinking subsyst ems r eady Reading commands syst em st at us= “Ready” display msg = “ent er cmd” display st at us = st eady ent r y/ swit ch machine on do: r un diagnost ics do: init iat e all subsyst ems ent r y/ subsyst ems r eady do: poll user input panel do: r ead user input do: int er pr et user input t ur n copier “of f ” not jammed paper f ull st ar t copies Making copies syst em st at us= “Copying” display msg= “copy count =” display message=#copies display st at us= st eady copies complet e paper t r ay empt y ent r y/ st ar t copies do: manage copying do: monit or paper t r ay do: monit or paper f low paper jammed pr oblem diagnosis syst em st at us= “Jammed” display msg = “paper jam” display message=locat ion display st at us= blinking ent r y/ paper jammed do: det er mine locat ion do: pr ovide cor r ect ive msg. do: int er r upt making copies load paper syst em st at us= “load paper” display msg= “load paper” display st at us= blinking ent r y/ paper empt y do: lower paper t r ay do: monit or f ill swit ch do: r aise paper t r ay not jammed Figure 7.6 Preliminary UML st at e diagram f or a phot ocopier 23

Validating Requirements

      Is each requirement consistent with the overall objective for the system/product?

Have stage?

all requirements been specified at the proper level of abstraction? That is, do some requirements provide a level of technical detail that is inappropriate at this Is the requirement really necessary or does it represent an add-on feature that may not be essential to the objective of the system?

Is each requirement bounded and unambiguous ?

Does each requirement have attribution? That is, is a source individual) noted for each requirement? (generally, a specific Do any requirements

conflict

with other requirements?

   Is each requirement achievable the system or product?

in the technical environment that will house Is each requirement testable , once implemented?

Does the requirements model properly reflect behavior of the system to be built.

the information, function and 24