Describe "schema dimensions" #43
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Master-part chapter: - Add point about part tables introducing new schema dimensions - Explain auto-populated masters cannot add dimensions, but parts can - Add "Schema Dimensions in Computed Tables" subsection - Update blob detection example to highlight blob_id as new dimension - Add schema dimensions to summary principles - Cross-reference Primary Keys chapter Populate chapter: - Add "Schema Dimensions and the Key Source" section - Explain why auto-populated tables cannot introduce dimensions - Show how this constraint makes key source well-defined - Explain part tables as solution for multi-output computations - Update blob detection case study to mention dimensions - Add Primary Keys to seealso references
…tegrity Natural vs Surrogate keys: - Natural keys: used outside the database to refer to entities in the real world - Key distinction is real-world usage, not origin (even system-generated IDs become natural if used externally) - Example: colony-generated animal IDs become natural keys when printed on ear tags - Surrogate keys: used only inside the database, not exposed to users - Example: internal post IDs on social media (users search by content, not ID) Partial entity integrity: - Sometimes only one direction of integrity is needed - Record→Entity: each record maps to one entity (but entity may have multiple records) - Entity→Record: each entity has a record (but records may be shared) - Example: social media preventing account sharing but allowing multiple accounts Entity integrity without natural keys: - Still possible but requires multi-step identification process - Database ensures uniqueness; external processes ensure entity-record matching - Comprehensive process design required outside the database
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