ACARA Digital Technologies Years 9–10 Definitions Worksheet: Entities, Relationships and Queries (Modules 433–451)
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Date:
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Key terms
Write what each term means, in your own words.
1
data redundancy
2
entity
3
attribute
4
junction table
5
ERD
6
crow's foot
7
ERD from a scenario
8
referential integrity
9
SQL
10
FOREIGN KEY (field) REFERENCES other_table(field)
Answer Key
ACARA Digital Technologies Years 9–10 · Modules 433–451 · Student wording will vary for definitions
1data redundancy — The same details stored again and again in one big table. It wastes space and risks typos or missed updates, like a customer's address copied onto every order.
2entity — A type of thing a database stores data about, such as a student, book or order. Each entity becomes one table, and its name is a singular noun.
3attribute — An attribute is one property of an entity, like a student's name or year level. Each attribute becomes one field (column) in the entity's table, and each instance of the entity is one record.
4junction table — A table that splits a many-to-many relationship into two one-to-many links by holding two foreign keys, such as Enrolment with studentId and subjectId.
5ERD — An entity relationship diagram draws each entity as a labelled box and each relationship as a line joining two boxes. Boxes list attributes, with PK and FK marked.
6crow's foot — ERD notation where a single bar at a line's end means one and a three-pronged crow's foot means many. The crow's foot end is the foreign key side of the relationship.
7ERD from a scenario — Find the entities, list their attributes, pick primary keys, then work out each relationship and draw it, with the foreign key on the many side.
8referential integrity — Every foreign key value must match an existing primary key in the related table, so no record points to something missing. The database blocks changes that break this.
9SQL — Structured Query Language, the standard language for asking a database to return data (SELECT) or to add, change or remove it (INSERT, UPDATE, DELETE).
10FOREIGN KEY (field) REFERENCES other_table(field) — Used in CREATE TABLE to link a column to another table's key. The database then only accepts values that match an existing key, so bad links are rejected.