Archive for the ‘keystrokes’ Category
Some definitions
From the research course:
External validity: Do the results hold across different settings? Can you generalise to a larger population?
Internal validity: Is there a causal relation between two variables? (no confounds)
** What does confounds mean in this context?
** What do we mean by power of a statistic?
The NIST speaker recognition evaluation: Overview methodology, systems, results, perspective.
Doddington, G.R., Przybocki, M.A., Martin, A.F., and Reynolds, D.A.
Speech Communication, 2000, 31(2-3), 225-254.
Identification: Deciding amongst a set of candidates who the biometric belong to.
Verification: Whether the biometric belongs to a particular candidate.
Closed set identification task aka closed world assumption: When actual subject is always one of the candidates.
Open set identification task: When actual subject may not be one of the candidates.
Sheep: well behaved subjects who dominate the target population.
Goats a minority group who tend to determine the performance of the system through their disproportionate contribution of errors.
Wolves are imposters who have unusally good success at impersonating many different target speakers.
Lambs are target speakers who seem unusually susceptible to many different imposters.
Weighted detection cost function:
Cdet = cmiss . Emiss . Ptarget + cfa . Efa . (1 – Ptarget)
cmiss and cfa are the relative costs of detection errors
Ptarget is the a priori probability of the target
Safeware quotes
Fault tree analysis was originally developed in 1961 by H. A. Watson at Bell Telephone Laboratories to evaluate the Minuteman Launch Control System for an unauthorized missile launch. FTA is primarily a means for analyzing causes of hazards, not identifying hazards.
Event tree analysis was developed by a group analysign the probability of “accidental release of radioactivity” who found that starting with this top level event led to a hopelessly complicated fault tree. Instead, they adapted the general decision tree fomalism to break up the problem into smaller parts to which FTA could be applied.
Cause-consequence analysis (CCA) combines forward and backwards search modes. Starts with a critical event and determines the causes of the event (using top-down or backward search) and the consequences that could result from it (forward search).
Hazards and Operability Analysis (HAZOP) focuses on safety AND efficient operations. Based on a systems theory model of accidents that assumes accidents are caused by deviations from the design or operating intentions. The technique creative thinking about al lthe ways in which hazards or operating problems might arise. (might be applicable). Makes use of guidewords.
Failure Modes and Effects Analysis (FMEA) is used to eatablish the overall probability that a product will operate without failure for a specific length of time, or that the product will operate a certain length of time between failures.
Fault harzard analysis. FMEA or FMECA with a broader and more limited scope. The scope is broadended by considering human error, procedural defiticiences, environmental conditions. It is more restricted because supposedly only failures that could result in accidents are considered.
State machine hazard analysis. Software and other component behaviour is modeled at a high level of abstraction, and faults and failures are modeled at the interfaces between the software and the hardware.
Building a safety case using GSN
From Tim Kelly’s thesis:
A goal structure does not necessarily replace the traditional form of the safety case, but can instead be thought of as a ‘road-map’ over the existing information – removing the burden of communicating potentially complex dependencies from the written text.
The steps in the development of a goal structure are:
- Identify goals to supported. Use a noun-phrase verb-phrase form.
- Define the basis on which goals stated.
- Identify strategy to support goals.
- Define basis on which strategy stated.
- Elaborate strategy (& therefore proceed to indentify new goals – back to Step 1), OR
- Identify basic solution.
Opus iti -- my little work 