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Lesson plan 07: Logical models and schemas
Represent ownership using keys, constraints, relationships, and relational operations.
Placement: Part 2: Representing and locating data.
Prerequisites: Lesson 06: Performance reasoning, plus the earlier dependency chain.
Learning outcomes
- Represent ownership using keys, constraints, relationships, and relational operations.
- Explain normalization and denormalization through update obligations and access costs.
- Choose a relational, document, or key-value representation against explicit atomicity and query requirements.
- Separate a general mechanism, a documented implementation choice, and an illustrative numerical assumption.
Teaching sequence
- Establish the motivating situation: A unique sword appears in two owners’ inventories after two services update duplicated ownership fields.
- Introduce the vocabulary and the correctness obligation before an optimization. Define relational algebra, keys, constraints.
- Develop the mechanism: Express facts and functional dependencies; distinguish logical constraints from physical indexes.
- Follow the complete worked example: An average of 40 items for 100000 players yields 4 million ownership rows. Explain the assumptions, intermediate units, and limiting interpretation.
- Extend the scenario to changed load, skew, or failure, explaining joins, normalization, denormalization, documents, key-value models.
- Connect the mechanism to a documented implementation and an alternative with a different workload fit. Close by stating the remaining cost and the next lesson dependency.
Required chapter material
Use a complete execution trace or worked calculation, supported by an annotated static diagram or table. Include language-neutral pseudocode or labeled SQL when it clarifies the mechanism. State preconditions, ownership, visibility, and failure boundaries for algorithms. Describe operational costs as well as the normal path. All questions raised in the narrative must be resolved in the text.
Visual explanation
An ownership schema marks primary and foreign keys; a before-and-after representation shows which facts are duplicated by denormalization. The accompanying prose explains the arrows, state changes, or table entries so the lesson remains understandable in a plain Markdown reader.
Editorial checks
Confirm that the numerical example agrees with its units and assumptions. Check that a faster path preserves the stated contract, or explicitly identify the changed guarantee. Keep hypothetical figures separate from product measurements. Explain both an appropriate use and a limitation of the case design. Check terminology against the glossary and links against the course index.