IB Computer Science Topic A3.2: Database Design Key Definitions

The maximum number of instances of one entity that can be linked to a single instance of another entity, which is either one or many. It is read separately for each end of a relationship line, giving the shapes 1:1, 1:N and M:N.

A composite key is a primary key that consists of two or more columns.

The highest-level description of a database, naming the entities it must store and the relationships between them. It carries no attributes, keys, data types or storage detail.

The structure of a database: the tables it holds, the attributes in each table, the relationships between them, and the constraints the data must obey. A schema defines organisation only and stores no records of its own.

Denormalization is the process of intentionally introducing redundancy into a normalized database to improve performance.

A diagram of a database design that shows each entity, the attributes it stores, and the relationships between entities, with the cardinality and modality of every relationship marked on the line.

A foreign key is a column (or set of columns) in one table that references the primary key of another table.

Attribute B is functionally dependent on attribute A if every value of A gives exactly one value of B. The dependency runs one way only, so A determines B does not mean B determines A.

An entity placed between two entities to resolve a many-to-many relationship, replacing it with two one-to-many relationships. It becomes a junction table holding one row per pairing, keyed on the two foreign keys together.

A description of a database that adds every attribute, primary key and foreign key to the conceptual design. It stays independent of any particular database management system.

The minimum number of instances of one entity that must take part in a relationship, which is either zero (optional) or one (mandatory). Also called optionality.

Normalization is the process of structuring a relational database into tables so that each fact is stored in exactly one place, carried out in stages called normal forms, each of which removes one kind of dependency problem.

A partial-key dependency is a non-key attribute that depends on only part of a composite primary key rather than on the whole key. Removing every partial-key dependency is the condition for second normal form.

The lowest-level description of a database, fixing a data type and size for every attribute and specifying indexes, file organisation and storage structures for one chosen database management system.

A primary key is a unique identifier for each record in a table.

The rule that every foreign key value must either match an existing primary key value in the referenced table or be NULL, so no row can point at a record that does not exist.

A transitive dependency, also called a non-key dependency, is a non-key attribute that depends on another non-key attribute instead of on the primary key. Removing every transitive dependency is the condition for third normal form.