Study guide: Describe Clean Structured Data
Validate schema id|count|category with count 0–9 and category red/blue. Inspect A|4|red,B|?|blue,C|2|red. State valid rows, missing-value handling and coverage.
Ideas to explain in your own words
- A data type describes how a value is represented and operated on. Text labels, numeric quantities and Boolean values have different meanings. An identifier with digits may still be text. Choosing a type should preserve the intended meaning and avoid operations that silently alter labels.
- A delimited file separates fields with a stated symbol and uses a schema to define their order. Without the schema, the same sequence may be misread. Real CSV also needs quoting rules for commas within a field. This lesson’s simple pipe-delimited rows contain no embedded separator.
- Validation checks whether values satisfy a stated contract. The same value can be acceptable in one field and invalid in another. A rule must specify required fields, allowed values and ranges before the learner decides how to handle records. Unknown values should not be silently replaced with invented ones.
- Missing values affect what a summary can claim. A known subtotal describes only recorded quantities. Reporting the number of known and missing entries helps a reader judge coverage. Our model knows which records are missing and does not estimate their values.
Useful vocabulary
- schema
- The fields, order and types expected in data.
- validation
- Checking values against stated requirements.
- coverage
- Which records have usable values for a summary.
Watch your reasoning
- Converting identifier 007 to number 7 loses its written leading zeros.
- Do not assume the first field is always a name or that a missing field is zero.
- A plausible value can still violate the defined range or type.
- Do not present the known subtotal as the complete total.
A worked review example
Identifier 007 must keep its exact characters. Which representation fits? The supported answer is Text. Use the field’s meaning, not just its appearance, to select a type. Converting identifier 007 to number 7 loses its written leading zeros. A data type describes how a value is represented and operated on. Records contain counts 3, 4, unknown. What is the known subtotal (not the complete total)? The supported answer is 7 known items. Applying the stated rule gives 7 known items. Add known values and report known/missing counts separately. Do not present the known subtotal as the complete total. Missing values affect what a summary can claim. Calculation: (3+4) = 7.
Make a practice plan
- Make a four-row summary, one row for each lesson, with its computing idea and one worked decision.
- Explain one tempting mistake using the actual supplied example.
- Complete the new unit review before consulting its explanations.
- Try the transfer task on paper and compare your evidence against the model response.