# Data Validation Checks (Range, Length, Type, Presence) - **Track:** Cambridge IGCSE™ Computer Science (0478 / 0984) (CAMBRIDGE IGCSE 0478) - **Module:** Section 7: Algorithm Design & Problem-Solving - **Estimated Duration:** 15 minutes - **Access:** Open Theory (All-Access for Interactive IDE & Autotests) --- ## Theory & Conceptual Background **Validation** is an automatic computer check performed by software to ensure that data entered into a system is **sensible**, **reasonable**, and **conforms to predefined rules** before it is processed or committed to a database. --- ## 1. The Critical Distinction > [!NOTE] > **Exam Golden Rule**: > Validation **DOES NOT** check if data is factually correct. > It only checks whether the data is acceptable according to the rules of the system. > For example: If a student types their name as "Dvaid" instead of "David", a validation check will accept it because "Dvaid" satisfies presence, length, and character-type checks! --- ## 2. The Six Standard Validation Checks | Validation Check | Definition / Rule Tested | Concrete Example | | --- | --- | --- | | **Range Check** | Verifies that a numerical or date value falls between an upper and lower boundary. | Month must satisfy $1 \le \text{Month} \le 12$. Exam score $0 \le \text{Mark} \le 100$. | | **Length Check** | Verifies that a string contains either an exact number of characters or falls within minimum/maximum limits. | Password must be $\ge 8$ characters. PIN text must contain exactly 4 characters; a separate format check can require digits. | | **Type Check** | Verifies that the value has the expected data type. | Age must be an integer. A STRING type alone does not restrict a surname to letters; a separate format rule is needed. | | **Presence Check** | Verifies that a mandatory data field has not been left blank or empty. | National Insurance number or Email address field cannot be empty. | | **Format Check** | Verifies that text conforms to a specific pattern or character mask. | Postal code matching `LLN NLL` (e.g. `CB2 1TN`). Date matching `DD/MM/YYYY`. | | **Check Digit** | A calculated value appended to the end of a numerical code to detect transmission, transcription, or transposition errors. | Final digit of an ISBN-13 book code or EAN-13 barcode recalculated via modulo arithmetic. | --- ## 3. Implementing Validation in Cambridge Pseudocode Input validation loops ensure incorrect entries are rejected immediately and re-prompted: ```pseudocode DECLARE StudentAge : INTEGER REPEAT OUTPUT "Enter student age (11 to 18): " INPUT StudentAge IF (StudentAge < 11) OR (StudentAge > 18) THEN OUTPUT "Invalid age! Must be between 11 and 18." ENDIF UNTIL (StudentAge >= 11) AND (StudentAge <= 18) OUTPUT "Valid age recorded: ", StudentAge ``` Notice that the `REPEAT ... UNTIL` loop checks the **valid** condition at the bottom to exit. --- ## Interactive Exercises & Autotest Specifications ### Exercise 1: Exam-Style Check: Match Validation Checks to Data Input Scenarios (Matching terms, 25 XP) **Instructions:** Match each validation check to the scenario where it provides the primary defense. **Starter Code:** ```text {"prompt":"Match each validation check with its application scenario:","left":[{"id":"chk_range","text":"Range check"},{"id":"chk_length","text":"Length check"},{"id":"chk_presence","text":"Presence check"},{"id":"chk_format","text":"Format check"},{"id":"chk_check_digit","text":"Check digit"}],"right":[{"id":"scen_range","text":"Ensuring an exam score falls between 0 and 100"},{"id":"scen_length","text":"Ensuring a telephone-number text field contains exactly 10 characters"},{"id":"scen_presence","text":"Ensuring an email address field is not left blank on registration"},{"id":"scen_format","text":"Ensuring a date of birth matches the pattern DD/MM/YYYY"},{"id":"scen_check_digit","text":"Recalculating a final barcode digit to detect misread numbers"}]} ``` **Autotest Expectations:** - **Validation checks matched to input scenarios**: `match_pairs` -> Expected: `{"chk_range":"scen_range","chk_length":"scen_length","chk_presence":"scen_presence","chk_format":"scen_format","chk_check_digit":"scen_check_digit"}` ### Exercise 2: Exam-Style Question: Classify Data Validation Checks (Fill in blank, 35 XP) **Instructions:** Identify the most appropriate validation check (Range check, Length check, Type check, or Presence check) for each requirement: 1. Ensuring an examination percentage mark is between 0 and 100: [blank_1] 2. Ensuring a postal code contains between 6 and 8 characters: [blank_2] 3. Ensuring an age field contains numeric digits only and no alphabetic characters: [blank_3] 4. Ensuring a mandatory email address input box is not left blank: [blank_4] **Starter Code:** ```text {"prompt":"Identify the validation check:","template":"1. Mark between 0 and 100: [blank_1]\n2. Postal code between 6 and 8 characters: [blank_2]\n3. Age must be an INTEGER: [blank_3]\n4. Field not left empty: [blank_4]","word_bank":["Range check","Length check","Type check","Presence check","Format check","Check digit","Lookup check"],"blanks":[{"id":"blank_1"},{"id":"blank_2"},{"id":"blank_3"},{"id":"blank_4"}]} ``` **Autotest Expectations:** - **Mark check is Range check**: `text_exact` -> Expected: `Range check` - **Postal code check is Length check**: `text_exact` -> Expected: `Length check` - **INTEGER data type is Type check**: `text_exact` -> Expected: `Type check` - **Non-blank is Presence check**: `text_exact` -> Expected: `Presence check` ### Exercise 3: Independent Practice: Accept a valid mark (Pseudocode, 30 XP) **Instructions:** Read integer marks until one lies in the inclusive range 0 to 100. Output the first valid mark. Write a complete program. Read inputs in the stated order. Output only the requested results, one per line, without input prompts. Test with your own values before submitting. **Starter Code:** ```text // Plan your solution, then write your program. ``` **Autotest Expectations:** - **Both boundaries invalid first**: `test_case` -> Expected: `{"inputs":[-1,101,0],"output":"0"}` - **Upper boundary**: `test_case` -> Expected: `{"inputs":[100],"output":"100"}` - **Ordinary value**: `test_case` -> Expected: `{"inputs":[-4,56],"output":"56"}`