The Spiral Model (SW process)

Formal verification is the use of mathematical methods to prove or disprove the correctness of a system's design with respect to a formal specification. Unlike testing, which can only show the presence of bugs for specific inputs, formal verification can prove their absence for all possible inputs. It involves creating a formal model of the system and using techniques like model checking or theorem proving.

A statistical measure of a process's ability to produce output within customer-defined specification limits. Unlike control charts, which track stability, Cpk quantifies capability. It measures how centered the process is between the specification limits and accounts for process variation. A higher Cpk value indicates a more capable process. The formula is \(C_{pk} = \min\left[\frac{USL - \mu}{3\sigma}, \frac{\mu - LSL}{3\sigma}\right]\).

Signal detection is the process of identifying potential causal relationships between a drug and an adverse event from large datasets, typically spontaneous reporting systems. It uses statistical methods, known as disproportionality analysis, to find drug-event combinations reported more frequently than expected. A common measure is the Reporting Odds Ratio (ROR), a value greater than one suggesting a potential signal that requires further investigation.

Jakob Nielsen, a prominent usability consultant in UI and webdesign mainly, defined usability through five quality components: Learnability (how easy is it for users to accomplish basic tasks the first time?), Efficiency (how quickly can they perform tasks once learned?), Memorability (can users reestablish proficiency after a period of not using it?), Errors (how many errors do users make?), and Satisfaction (how pleasant is it to use?).

Verification and validation (V&V) are distinct processes. Verification ensures a product meets its specified requirements ("Are you building it right?"). Validation ensures the product meets the user's actual needs and intended use ("Are you building the right thing?"). They are complementary activities within quality management, often performed sequentially or in parallel to ensure both correctness and usefulness.

The repeatability limit, \(r\), is a critical value derived from the repeatability standard deviation (\(s_r\)). It represents the maximum expected absolute difference between two single test results, obtained under repeatability conditions, with a 95% probability. It is commonly calculated as \(r = 2.8 \times s_r\). If the difference exceeds \(r\), the results are considered suspect.

BFT (acronym of Byzantine Fault Tolerance) is a property of a system that allows it to continue operating correctly and reach consensus even if some of its components fail in arbitrary, unpredictable ways, including malicious behavior (Byzantine failures). This is a much stronger guarantee than tolerating simple crash failures. It requires a minimum of \(3f+1\) total components to tolerate \(f\) faulty, malicious components.

RAID (acronym of Redundant Array of Independent Disks) is a data storage virtualization technology that combines multiple physical disk drives into one or more logical units for data redundancy, performance improvement, or both. Different RAID levels provide varying balances of reliability, availability, performance, and capacity. For example, RAID 1 mirrors data across two disks, while RAID 5 stripes data and parity across at least three disks.