as its primary key. Each of the attributes that makes up the primary key is a simple key because each represents a unique reference when identifying a student in one instance and a module in the other, so this key is a compound key. In contrast, using the same example, imagine we identified a student by their firstName + lastName. In a table representing students our primary key would now be firstName + lastName. Because students can have the same firstNames or the same lastNames these attributes are not simple keys. The primary key firstName + lastName for students is a composite key. See also Relational database Candidate key Primary key Alternate key Foreign key Unique key Surrogate key Superkey External links Composite Inverse Functional Properties: for an equivalent notion in the Semantic Web Relation Database terms of reference, Keys: An overview of the different types of keys in an RDBMS Different types of keys in a database: An overview of all the types of keys that are used in an RDBMS Data modeling ru:Составной ключ