Recognises a sentinel value standing in for null
https://knobit.org/id/knobit/K-629
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| Context functions | Result evaluation |
|---|---|
| Knobit creation methods | AI generated |
| Knobit types | Skill |
| LCG purposes | Assessing the learner's knowledge or skill state |
| LCG purposes | Selecting an assessment task or learning activity |
| action verb | Recognises en |
| applies knowledge | Explains null semantics and three-valued logic |
| assessment criterion | Flags the deficient case and passes the acceptable one. Deficient: `account_opening_date = '1900-01-01'` when unknown; `branch_id = -1`; open-ended validity as `NULL` in one table and `9999-12-31` in another Acceptable: `NULL` for unknown. Where a value is required, one project-wide convention recorded in config (open-ended `valid_to`), and a dimension's unknown member as a labelled row that every query sees, not a magic number in a measure en |
| assessment method | skill-tests task: Loan application physical model on Snowflake (physical design anomaly skills) en |
| conforms to profile | https://oppekava.edu.ee/a/Knobitite_kirjeldamise_ja_seostamise_reeglid#LCG-KNOBIT-0.1 |
| dcterms:identifier | K-629 |
| dcterms:license | https://creativecommons.org/licenses/by/4.0/ |
| dcterms:source | Review checklist 04-physical, row 19; Karwin, Fear of the Unknown; Codd 1979 §2.3 en |
| depends on knobit | Recognises an attribute with several meanings |
| expected result | The sentinel and the null or status column replacing it en |
| owl:sameAs | https://bitbucket.org/reffa/ontology/id/knobit/data-modelling/06-physical/K-629 |
| rdfs:label | Recognises a sentinel value standing in for null en |
| schema:creativeWorkStatus | accepted |
| schema:isPartOf | Data modelling (DAMA-DMBOK2) |
| skos:altLabel | Sentinel value in place of null, or null with a business meaning (physical model) en |
| skos:definition | A real-looking value standing for "unknown" or "not applicable", or a null that means something specific and different in different tables. Sentinels pass every constraint and end up in totals and averages. A specific form of logical row 6 at the physical level. en |
| skos:prefLabel | Recognises a sentinel value standing in for null en |
| target object | real-looking value meaning unknown or not applicable en |
Used by
| depends on knobit | Recognises a default inventing a business fact |
|---|---|
| includes knobit | Designs a physical data model for the target platform without introducing anomalies |
| requires knobit | Design the physical data model |
| schema:supersededBy | Sentinel value in place of null, or null with a business meaning (physical model) |