2/16/06 Page 1Loui Some Notes from Sommerville Software Engineering 7 CS436 (material for quiz)

2/16/06 Page 2Loui FAQ: What is software? Generic products (global reach) Customized products (bespoke, commissioned)

2/16/06 Page 3Loui FAQ: What is software engineering? Engineering discipline –Making things work –Theories and methods used selectively –Solutions to problems –Constraints –NOT software art or software authorship Aspects of software production –Tools, methods, theories –Project management

2/16/06 Page 4Loui FAQ: What is software engineering? Costs –Design & modeling –Development Support, data, communications, algorithm, security & access, interface –Testing & reporting –Evolution Aims –Required functionality & performance –Maintainable, dependable, usable

2/16/06 Page 5Loui FAQ: Process Models Workflow model –Sequence of activities, I/O dependencies of HUMAN actions Dataflow model –Data transformation activities, I/O dependencies of program components Role/Action model –Roles of people involved & responsibilities

2/16/06 Page 6Loui FAQ: Key challenges Heterogeneity challenge –Systems are distributed –New systems + legacy systems –Different programming languages / platforms Delivery challenge –Process & quality are time consuming –Business changes rapidly Trust challenge –Do you trust web sites? –Do you trust aircraft control software?

2/16/06 Page 7Loui FAQ: Types of methods System model –Objects, data flow, state machines Rules –Entities should have unique names –Glossary Recommendations –No object should have more than 7 sub-objects –Milestone division of time –Limit on the complexity of each component Guidance –Objects should be documented –Versions should be published through cvs

2/16/06 Page 8Loui FAQ: Ethics & Professional Responsibility To the public To the client or employer To the product To integrity and independence of professional judgment To ethical management of software & people To the profession (uphold integrity and reputation) To colleagues (be fair and supportive) To self (practice lifelong learning)

2/16/06 Page 9Loui System design Partition requirements Identify subsystems Assign requirements to subsystems Specify subsystem functionality Define subsystem interfaces

2/16/06 Page 10Loui Kinds of Legacy Systems System hardware Support software & platform Application software Application data Business processes Business policies and rules

2/16/06 Page 11Loui Kinds of Critical Systems Safety-critical systems –Kill people when they fail Mission-critical systems –Kill plans when they fail Business-critical systems –Kill the budget when they fail

2/16/06 Page 12Loui Safety Terminology (book) Accident –Unplanned event Hazard –Condition causing or contributing to accident Damage –Measure of loss Hazard severity –Assessment of the worst possible damage Hazard probability –Probability of events which create a hazard Risk –Measure of the probability that the system will cause an accident

2/16/06 Page 13Loui Safety Terminology (Loui) Accident –Unplanned event Hazard –Condition causing or contributing to accident Damage –Measure of loss Hazard severity –Assessment of the worst possible damage Hazard probability –Probability of accidents due to the hazard Risk –Measure of hazard severity and hazard probability conditioned upon specific action or non-action

2/16/06 Page 14Loui Security Terminology (book) Exposure –Possible loss or harm Vulnerability –Weakness that could be exploited to cause loss or harm Attack –Exploitation of vulnerability Threats –Circumstances that have potential to cause loss or harm Control –Protective measure to reduce vulnerability

2/16/06 Page 15Loui Security Terminology (Loui) Vulnerability –Weakness that could be exploited to cause loss or harm Exposure –Measure of appearance of conditions of vulnerability Attack –Exploitation of vulnerability Threats –Circumstances that precondition an attack Countermeasures –Protective measure to reduce vulnerability or exposure