Find the entities in a real-world brief
See this course’s project requirements
A four-table equipment-loan schema with stable keys, relationship definitions, integrity rules and checked edge cases.
Keep your working files in your own notebook or software. Save a private description, checklist, and work link in My Proof.
What to include
- Four entity definitions and base row counts.
- Stable primary keys and foreign keys.
- Relationship sketch and trace.
- Dependency/redundancy example.
- Integrity rules, three edge cases and limits.
Review and revise
Use these criteria to check your work and choose what to improve.
- Objects and events remain distinct.
- Keys reconstruct every required relationship.
- Facts are stored with their proper owner.
- Constraints and case decisions match the stated policy.
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The idea in everyday life
Design a small fictional equipment-loan system before writing retrieval queries.
An entity is something whose identity and facts need to be recorded independently.
Find the entities in a real-world brief — guided practice
Separate equipment types, physical items, borrowers and loan events.
Work in design.md or on paper; no database installation is required. Fictional equipment library: types T1=Camera, replacement units 200; T2=Tripod, replacement units 40. Items I1 and I2 have type T1; I3 has type T2. Borrowers B1=River and B2=Sky are aliases. Loans: L1, I1, B1, returned=1; L2, I1, B2, returned=0; L3, I3, B1, returned=0. Rule: returned is 0 or 1; each item may have at most one active (returned=0) loan. Keep the base rows available throughout all six lessons.
1. Read the repeated flat record
Write the flat version of L1 and L2: each repeats I1, T1, Camera and 200, but borrower/returned differ.
You should see: Camera facts repeat across two loan events.
Repeated facts reveal different kinds of things mixed together.
2. Name four entities
Write Type, Item, Borrower and Loan, with one sentence defining each.
You should see: Type is a model/category; Item is one physical object; Loan is one borrowing event.
A camera type and a particular camera are not interchangeable.
3. Assign facts
Put label/cost with Type, type ID with Item, alias with Borrower, and item/borrower/returned with Loan.
You should see: Every supplied fact has an owner.
Facts should be stored with the thing they describe.
4. Count the base rows
Count entities by category from the setup.
You should see: 2 types, 3 items, 2 borrowers and 3 loans.
Counting tests whether events and objects were confused.
What to finish
Four entity definitions and base row counts.
Watch for this
Creating a new physical-item row every time the same item is borrowed.
How can I tell I understand it?
Complete the changed case, explain your result, and pass the three application checks.
Quick knowledge check
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Answer all 3 questions above and get at least 2 right. You can review the explanations and try again.
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Database Design Course - Learn how to design and plan a database for beginners
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Source & access notes · checked 2026-09-12
Opened and inspected on 2026-09-12: Entities, keys and relationship multiplicities.
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Source & access notes · checked 2026-09-12
Metadata retrieved and inspected on 2026-09-12: exact title and channel confirmed through YouTube oEmbed. Playback and full video content were not tested. Optional overview; the written lesson and supplied practice stand alone.
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