CSS 342 Quiz 1

Agile Models Answer- Extreme Programming Scrum DSDM KanBan Perspective Models Answer- Spiral Waterfall Spiral Into Waterfall Staged Delivery Sashimi Mixed Models Answer- Unified Process Evolutionary Programming Code and Fix Software Engineering Answer- goal is to address the problems of building large software systems Software Engineering Definition Answer- "A discipline that deals with the building of software systems that are so large or so complex that they are built by a team or teams of engineers" [Ghezzi, Jazayeri, Mandrioli] Programming Answer- - small project - just me - build what I want - one product - few sequential changes - short-lived - cheap - small consequences engineering Answer- - huge project -teams -build what they want - family of products - parallel changes -long live -costly -large consequences Software Engineering Answer- -Organizing teams to cooperatively build systems -Determining what to build -Software architecture -Analysis and testing -Lifecycle system engineering Ariane 5, Flight 501 Answer- -Re-used code from Ariane 4, overflowed a 16 bit integer storing horizontal velocity. -backup fail Flaw of Ariane 5 Answer- -Conversion from 64-bit floating point to 16-bit signed integer -Flaw could have been detected by more testing - although they did use rigorous testing -Flaw was in a component that was reused from Ariane 4 -Flaw in the design - an identical backup system works for hardware malfunction, but not software. The backup component could have calculated the best estimate Therac-25 Answer- deadly doses of radiation - shows need for software control, due diligence, testing, and resolution of bugs Therac-25 Cause and Cost Answer- 3 dead & 3 injured -Operator typed 'x' (X-ray mode) instead of 'e' (electron mode) -Tried to correct error, the software malfunctioned, and the operator was unaware that the mode was not corrected -Earlier versions of the machine used mechanical safety devices, instead of software Why difficult to get error free software? Answer- -Complexity -Conformity -Changeability -Invisibility - human error - poor interface - inadequate abstraction - lack of solid mathematical/ engineering foundation Complexity Answer- No two software parts are alike (other unifed into one) and complexity grows non-linearly with size (Scaling-up is necessarily an increase in the number of different elements) Unlike car where wheels same and doors the same. Conformity Answer- software is required to conform to its operating environment and hardware, which are often out of its control; this burden is especially difficult since software is often used to mask or fix problems in these underlying strata Human institutions (govt, laws) Existing systems (CS languages) Different for each context (software vs phone) changeability Answer- software can change in nearly infinite ways, and can come from many sources: new applications, users, machines, standards, laws, hardware problems, and so on. -like cars and computers superseded with later models - building bridge $$ to change so change less often -Users want additional functionality -Software survives beyond the normal life of the machine for which it was written Invisibility Answer- software has no physical form and therefore is not constrained by physical laws, per se. This also means that there is no natural or obvious representation of what software "looks" like. Software cannot be "observed" in a conventional sense. - floor plan - easier to see how to fix - software not inherently embedded in space and that is difficult and harder to convey SE vs. Science Answer- empirical studies; theories characterizing aggregate system behavior (e.g. reliability) SE vs. Management Answer- organizing teams, directing activities, correcting problems SE Vs. Human Factors Answer- user task understanding and modeling; UI design SE vs. Engineering Answer- tradeoffs, canonical solutions to typical problems -Tradeoffs and representative qualities Pick any two: -Good, fast, cheap -Scalability, functionality, performance SE vs. Architecture Answer- + phases, user input/review, user looks but minimal involve - lots of domain knowledge, know what kind of change each stage, progress easy to measure Legislation Answer- + intangible, unforeseen consequences, hard to see progress, importance of careful review - difficult to test and not rigorous discipline SDLC Activites Answer- - requirements -architecture - implementation - testing Q/A - maintenance Why software process models? Answer- Provide structure to the software development process -Coordination and teamwork -Identification of deliverables Scheduling and milestones -Improve likelihood of success of projects -Reduce risk throughout project Project Management Answer- - ensure project meets requirements - budget, schedule, and resources (including people) WBS Answer- -Build a tree with the root labeled by the major activity of the project -Each node can be broken down into smaller tasks. -Repeat step 2 until the task can be estimated in terms of size, difficulty, and resource requirements Gantt Answer- built on WBS activities must be define - plan order (whether sequence or parallel) - estimated length vs. slack - resource plan and scheduling - no show dependencies PERT (Program Evaluation and Review Technique) Answer- - show dependencies - list all activities req and est time - det. dependencies - variations Critical Path Answer- path is a path where any delay on the path will case a delay in the project PM monitor the critical path PERT important features Answer- - forces/ help PM plan - show dep. among tasks and identifies critical path - exposes possible parallelism in activities and thus help resource allocation - scheduling & simulation of alt. schedules - enable PM monitor & control project prescriptive Answer- -Aka "planned" approach - An ordered approach to the software process with a defined structure and expected set of activities and work products - Promote controls that improve project acceptance, decision making, and project management agile Answer- - simple to learn