Validation & Verification

Validation is the process of checking that data entered is REASONABLE and MEETS CRITERIA before it is stored or processed. It is performed at INPUT time — the program checks the value immediately and either accepts or rejects it.

• Performed at input time — the check runs as the data is entered.
• Checks reasonableness — does the data meet the defined rules?
• Does NOT check correctness — a valid age (e.g. 25) may still be the wrong age for the person.
• Five common types — Range, Length, Type, Presence, Format.

A range check verifies that an input value falls within a specified lower and upper bound. It is typically used for numeric data such as age, exam score, temperature, or quantity.

DECLARE Age : INTEGER
OUTPUT "Enter age: "
INPUT Age
IF Age >= 0 AND Age <= 120 THEN
  OUTPUT "Valid age"
ELSE
  OUTPUT "Invalid age"
ENDIF

• Inclusive bounds — >= and <= accept values AT the boundary.
• Two conditions joined with AND — both must be true for the value to pass.
• Typical uses — age 0–120, exam score 0–100, month 1–12, day 1–31.
• Rejects — out-of-range values such as Age = 150 or Score = -5.

A length check verifies that a string input has the correct number of characters. The rule can be a minimum length, a maximum length, or an exact length. It uses the built-in LENGTH() function.

DECLARE Password : STRING
OUTPUT "Enter password: "
INPUT Password
IF LENGTH(Password) >= 8 THEN
  OUTPUT "Valid password"
ELSE
  OUTPUT "Password too short"
ENDIF

• Minimum length — LENGTH(Pwd) >= 8.
• Maximum length — LENGTH(Tweet) <= 280.
• Exact length — LENGTH(Phone) = 11.
• Uses LENGTH() built-in — returns the character count as an INTEGER.

A type check verifies that the input is of the correct data type (e.g. INTEGER, REAL, STRING, BOOLEAN). A presence check verifies that a field is not empty — i.e. the user has supplied a value.

• Type check — input must match the declared data type. Declaring Age : INTEGER and using INPUT Age rejects non-numeric input.
• Presence check — input must not be empty. Test with IF Name = "" THEN.
• Used together — a name field needs both a presence check (not empty) AND a type check (must be STRING).

DECLARE Name : STRING
OUTPUT "Enter name: "
INPUT Name
IF Name = "" THEN
  OUTPUT "Name is required"
ELSE
  OUTPUT "Valid name"
ENDIF

The above example performs a presence check on the Name field. If the user presses Enter without typing anything, Name becomes the empty string "" and the check fails with "Name is required".

Verification is the process of checking that data has been ACCURATELY COPIED or ENTERED. It is performed AFTER data entry — not at input time. The two main methods are double entry and visual check (proofreading).

• Double entry — user enters the same data twice; system compares the two entries.
• Visual check — user proofreads the entered data against the source.
• Performed AFTER input — not at the moment of entry.
• Catches transcription errors — e.g. typing 25 instead of 52.

DECLARE Email1, Email2 : STRING
OUTPUT "Enter email: "
INPUT Email1
OUTPUT "Confirm email: "
INPUT Email2
IF Email1 = Email2 THEN
  OUTPUT "Email verified"
ELSE
  OUTPUT "Emails do not match - re-enter"
ENDIF

This is double-entry verification. The user enters the email address twice. If the two entries match, the data is verified. If they differ, the user must re-enter — the mismatch suggests a typing error.

A quick recap of everything covered on validation and verification:

• Validation = reasonable — Checks data entered is reasonable and meets criteria.
• Verification = accurately entered — Checks data has been accurately copied or entered.
• Validation at INPUT time — Performed as data is entered — immediate accept/reject.
• Verification AFTER input — Performed after entry — comparison or proofread.
• Five validation types — Range, Length, Type, Presence, Format.
• Two verification methods — Double entry (enter twice, compare), Visual check (proofread).
• Range check — IF Value >= Min AND Value <= Max THEN ... — inclusive bounds.
• Length check — IF LENGTH(Str) >= N THEN ... — uses the LENGTH() built-in.
• Type check — Declared data type acts as implicit type check during INPUT.
• Presence check — IF Field = "" THEN reject — field must not be empty.
• Validation ≠ correctness — A valid value (age 25) may still be wrong for the person.
• Both needed — Validation + verification together give the best data integrity.