Designing the file structure
A file here means a table of records. A record is all the data about one thing. A field is one item of data in a record.
For each field the designer chooses a field name, a data type and a field length (the maximum number of characters).
Coding of data means storing short codes instead of long words, for example M or F, Y or N.
?Why?Codes save storage space, are quicker to type and are easier to validate. There are only a few allowed values, so mistakes are easy to spot.
!Watch outPhone numbers and IDs with leading zeros are stored as text, not numbers. A numeric field would drop the leading zero (0034 would become 34).
Validation: what it is and why we need it
Validation is an automatic check, done by the computer, that data entered is sensible and allowed.
It stops impossible or unreasonable data getting into the system.
Validation cannot tell if data is correct. It can only tell if it is reasonable. An age of 15 passes a range check even if the student is really 14.
e.g.ExampleTry the toy: type 19 in the Age box, which has a range check of 11 to 18. Then type 'abc' there for a type check. Leave the Surname box empty to trigger the presence check.
!Watch outDo not mix up validation and verification. Verification checks data was copied correctly (double entry, visual check). Validation checks data is sensible.
There is something to try for this step in the IGCSE library.
The check digit, worked through
A check digit is an extra digit added to the end of a code. It is calculated from the other digits.
When the code is typed or scanned, the computer recalculates the check digit. If it does not match, there is an error.
It catches mistyped digits and transposition errors (two digits swapped, such as 45 typed as 54).
ISBN-13 (the number on books) uses weights of 1 and 3 and modulo 10. Modulo 10 means the remainder after dividing by 10.
e.g.ExampleFind the check digit for the first 12 digits of an ISBN: 978030640615
Step 1: multiply digits by 1, 3, 1, 3 … in turn:
9×1=9, 7×3=21, 8×1=8, 0×3=0, 3×1=3, 0×3=0,
6×1=6, 4×3=12, 0×1=0, 6×3=18, 1×1=1, 5×3=15
Step 2: add them: 9+21+8+0+3+0+6+12+0+18+1+15 = 93
Step 3: remainder after dividing by 10: 93 MOD 10 = 3
Step 4: subtract from 10: 10 − 3 = 7
(If the remainder is 0, the check digit is 0.)
Full ISBN: 978-0-306-40615-7
Spot an error: someone types 9780306406517 (1 and 5 swapped).
The weighted total becomes 92 instead of 100 (counting the check digit 7 × 1).
92 is not a multiple of 10, so the computer rejects it.
?Why?Multiplying by different weights means swapped digits give a different total. A plain sum would not catch a swap, because 1+5 and 5+1 are the same.
Input formats: data capture forms
A data capture form collects data from a person. It can be on paper or on screen.
A good form has a clear title, instructions, logical field order and enough space for each answer.
On-screen forms can use drop-down menus, radio buttons (choose one) and tick boxes (choose any). These limit what can be entered, so there are fewer errors.
Paper forms may use boxes with one character per box, so writing is easier to read or scan by OCR.
e.g.ExampleLibrary sign-up screen:
Title: 'New library member'
StudentID [S_____] (format shown as a hint)
Surname [__________]
Year group: drop-down 7, 8, 9, 10, 11, 12, 13
Gender: radio buttons F / M
Buttons: Save Clear Help
!Watch outExam answers about forms need specific features: 'use a drop-down for year group' earns a mark, 'make it look nice' does not.
Output formats: screen layouts and report layouts
Output formats decide how results are shown: on a screen or in a printed report.
A screen layout shows where each item appears, the fonts, the colours and any buttons.
A report layout shows the title, column headings, the order of fields, page numbers and totals.
The designer plans these early, so users can agree them before any building starts.
e.g.ExampleWeekly overdue report layout:
Title: Overdue books, week ending 13/11/2026
Columns: Tutor group | Surname | Book title | Days overdue
Sorted by tutor group, then surname
Footer: page 1 of 3, total overdue books: 47
?Why?Showing users the layouts before building means changes are cheap. Changing a finished report later costs time and money.