Validation, verification and trace tables · ⁨验证、核对与追踪表⁩

Checking and tracing

• When data is entered, we check it to reduce mistakes.
• Validation 验证 checks it is sensible; verification 核实 checks it was copied correctly.
• A trace table 追踪表 follows an algorithm step by step.

Validation

• Validation checks data is sensible and follows the rules (it can't check the data is true).
• Range check 范围检查 (between limits), length check 长度检查 (right number of characters), type check (right kind of data), presence check 存在性检查 (not blank), format check (right pattern, e.g. dd/mm/yyyy), and a check digit (an extra digit confirming a number).

Every algorithm decomposes into input, processing and output — here, finding the average of three marks.

Verification

• Verification checks data was copied or entered correctly (no typing mistakes).
• Visual check — a person compares the typed data with the original.
• Double entry — the data is entered twice and the two copies are compared.

Linear search checks each item in turn from the start until it finds the value.

Trace tables and test data 测试数据

• A trace table records each variable's value as an algorithm runs — to check it works or to find out what it does.
• Test data types: normal (accepted), abnormal (rejected), extreme (largest/smallest allowed), boundary (the values on each side of a limit, e.g. 120 and 121).

A trace table records each variable's value as the program runs

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