Computer-Science-A-level-Ocr
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3-3-networks8 主题
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3-2-databases7 主题
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3-1-compression-encryption-and-hashing4 主题
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2-5-object-oriented-languages7 主题
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2-4-types-of-programming-language4 主题
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2-3-software-development5 主题
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2-2-applications-generation6 主题
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2-1-systems-software8 主题
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1-3-input-output-and-storage2 主题
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1-2-types-of-processor3 主题
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1-1-structure-and-function-of-the-processor1 主题
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structuring-your-responses3 主题
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the-exam-papers2 主题
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8-2-algorithms-for-the-main-data-structures4 主题
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8-1-algorithms10 主题
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7-2-computational-methods11 主题
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7-1-programming-techniques14 主题
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capturing-selecting-managing-and-exchanging-data
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entity-relationship-diagrams
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data-normalisation
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relational-databases
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hashing
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symmetric-vs-asymmetric-encryption
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run-length-encoding-and-dictionary-coding
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lossy-and-lossless-compression
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polymorphism-oop
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encapsulation-oop
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inheritance-oop
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attributes-oop
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methods-oop
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objects-oop
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capturing-selecting-managing-and-exchanging-data
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6-5-thinking-concurrently2 主题
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6-4-thinking-logically2 主题
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6-3-thinking-procedurally3 主题
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6-2-thinking-ahead1 主题
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6-1-thinking-abstractly3 主题
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5-2-moral-and-ethical-issues9 主题
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5-1-computing-related-legislation4 主题
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4-3-boolean-algebra5 主题
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4-2-data-structures10 主题
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4-1-data-types9 主题
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3-4-web-technologies16 主题
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environmental-effects
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automated-decision-making
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computers-in-the-workforce
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layout-colour-paradigms-and-character-sets
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piracy-and-offensive-communications
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analysing-personal-information
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monitoring-behaviour
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censorship-and-the-internet
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artificial-intelligence
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the-regulation-of-investigatory-powers-act-2000
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the-copyright-design-and-patents-act-1988
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the-computer-misuse-act-1990
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the-data-protection-act-1998
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adder-circuits
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flip-flop-circuits
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simplifying-boolean-algebra
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environmental-effects
referential-integrity
Referential Integrity
What is referential integrity?
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In A Level Computer Science, referential integrity ensures consistency between related tables in a relational database
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Maintains valid relationships between primary and foreign keys
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There should not be foreign keys for which a matching primary key in the linked table does not exist
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Foreign key constraints
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Value in a foreign key field must either:
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Match a primary key value in the related table, or
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Be null (if allowed)
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Enforce referential integrity
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Rules:
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Cascade actions
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CASCADE: automatically makes changes to related records
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SET NULL: sets foreign key value to null in related records
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SET DEFAULT: sets foreign key value to its default in related records
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NO ACTION/RESTRICT: prevents changes if related records exist
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Update or delete actions will take effect everywhere in the database automatically
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Types:
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Benefits and drawbacks of referential integrity
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Benefits |
Drawbacks |
|---|---|
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Ensures data consistency and accuracy |
Can impact performance due to additional checks |
|
Prevents orphaned records |
May require additional planning and design |
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Maintaining referential integrity
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Use database management systems (DBMS) with built-in support
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Implement triggers to enforce custom referential integrity rules
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Regularly validate and clean up data to ensure consistency
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Worked Example
A hotel uses a computer system to keep track of room bookings. The hotel staff are able to query a database to discover which rooms are booked or which rooms are free
The hotel booking database enforces referential integrity.
Explain what is meant by the term ‘referential integrity’ and how this could potentially be broken
[2]
Answer:
Database/relationships are consistent and each foreign key links to an existing/valid primary key [1]
If a primary key is deleted, foreign keys that link to it are no longer valid so they should also be deleted – this is known as a cascaded delete [1]
Responses