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The UNIQUE function filters duplicate items from a collection. An expression resulting in a collection, never contains duplicate values. A subexpression with the COLLECT statement however, can contain duplicates. See the note on collections and duplicates for more info.

Syntax

 UNIQUE ( collection )

• collection - A collection of attribute or entity instances.

Examples

Suppose the following model.

• COLLECT Person.name FROM ALL Person = "Kim”, “Rick”, “Bob” (a result never contains duplicate values)
• SIZE ( COLLECT Person.name FROM ALL Person ) = 4 (a subexpression can contain duplicate values)
• SIZE ( UNIQUE ( COLLECT Person.name FROM ALL Person ) ) = 3 (the collection holds three unique values)

This function returns TRUE if the items in a collection are all present in another collection.

Syntax

 collection1 SUBSET OF collection2

• collection1 - The collection that is tested to be a subset of the second collection.
• collection2 - The collection that is tested to hold all the items in the first collection.

Return type

• boolean

Diagram

Examples

• ('a', 'b', 'c') SUBSET OF ('a', 'b', 'c', 'd') = TRUE
• ('a', 'b', 'c', 'd') SUBSET OF ('a', 'b', 'c') = FALSE
• (Person.hobbies) SUBSET OF ([“Tennis”, “Soccer”, “Music”]) = TRUE if Person.hobbies = “Tennis”, “Soccer”
• (Person.hobbies) SUBSET OF ([“Tennis”, “Soccer”, “Music”]) = UNKNOWN if Person.hobbies = ?
• (Person.hobbies) SUBSET OF ([“Tennis”, “Soccer”, ?]) = FALSE if Person.hobbies = “Tennis”, “Soccer”
  • Because: ["Tennis", "Soccer", ?] evaluates to [?] and (Person.hobbies) SUBSET OF [?] = FALSE

• ('a', 'b', 'c') SUBSET OF (['a', 'b', 'c']) will result in an error.