lesson
Relationships avoid repeated inconsistent copies
1 · Learn
A relational model can separate entities into tables and connect them through keys. For example, a course table stores course details while an enrolment table links student IDs to course IDs. Repeating course titles in every unrelated record makes updates harder to keep consistent.
A foreign key refers to another record's key; it is not the same as copying every field. Relationships need rules for missing or deleted referenced records.
2 · Worked example
Changing one course title can update its displayed name wherever the relationship is used, without changing the course's identity.
3 · Your turn
Which two identifiers could an enrolment record use to link a student and a course?
Check your answer
Student ID and course ID.
4 · Apply your learning
Draw a small invented schema and explain why deleting a course with historical enrolments needs an explicit policy.
Adult guidance and safety
Work in an approved local sandbox with invented records and test accounts. Do not access other people's systems or collect real credentials. Practical project evidence is required in addition to these explanations; this is not a specified GCSE Computer Science course.
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Check a calculation · Year 5 onward
Use this only when your teacher or adult allows a calculator for the task. Show your thinking first. It does not replace mental or written arithmetic and does not mark your lesson answer.
Powers, roots and trigonometry · Year 7 onward
Use only when the task allows a calculator. Choose one operation at a time and record your working. Trigonometry here always uses degrees (DEG), not radians. Inverse sine, cosine and tangent return an angle, not a reciprocal. Keep exact fractions and π in answers when requested.
Approximate numerical results use up to 12 significant digits. Inverse sine returns −90° to 90°, inverse cosine 0° to 180°, and inverse tangent −90° to 90°; these are principal values, not every possible solution of a trigonometric equation.
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