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Learn more about the collection functions EXISTS, EACH, ALL, COLLECT FROM WHERE, COLLECT FROM NAMED WHERE, COLLECT, UNPACK, LIST, SIZE, UNIQUE, SUBSET OF, UNION, INTERSECTION, DIFFERENCE, SYMMETRIC_DIFFERENCE.

Overview

Function	Description
`EXISTS`	Determines

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Table of Contents

minLevel	2

EXISTS

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whether an instance of a specified entity exists, optionally meeting certain criteria

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Syntax

Code Block
EXISTS instances [WHERE condition]

instances - Instances to search.
condition - boolean expression that represents the criterion the instance has to meet.

Return type

boolean

Examples

Suppose the following data model.

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EXISTS Person = TRUE

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.

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EXISTS Person WHERE (Person.gender = “m” AND Person.age > 35) = TRUE

EACH Determines

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type	note

The return value of a boolean can be TRUE, FALSE or UNKNOWN.

EACH

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whether all instances of a specified entity meet a certain criteria

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Syntax

Code Block
EACH instances WHERE condition

instances - A collection of instances to search.
condition - Boolean expression that represents the criterion the instance has to meet.

Return type

boolean

Examples

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.

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EACH Person WHERE (Person.age < 18) = FALSE
EACH Person WHERE (Person.age > 18) = TRUE
EACH Person WHERE (Person.age < 20) = FALSE
EACH Person WHERE (Person.gender = “m” OR Person.age > 35) = FALSE
EACH Person WHERE (Person.gender = “m” OR Person.age > 20) = TRUE


`ALL`	Creates

ALL

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a collection of all instances of a specified entity.

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Syntax

Code Block
ALL entity

entity - Entity of which to collect all its instances.

Return type

collection of entity instances

Examples

Suppose the following data model. The Parent and Child entities both have Person as base entity.

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ALL Parent = [ Parent_1 , Parent_2 ]

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ALL Person = [ Parent_1 , Parent_2 , Child_1 , Child_2 , Child_3 , Child_4 ]

COLLECT FROM [WHERE]

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Creates a collection of entity or attribute instances (meeting certain criteria

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Syntax

Code Block
COLLECT entity \| attribute FROM collection [WHERE expression]

entity or attribute - Entity or attribute to collect.
collection - A collection of entity instances.
expression - Boolean expression that represents the criterion the instance has to meet.

Return type

collection of entity instances
collection of attribute values

Examples

Suppose the following model. Entity Teacher has a multivalued relation with entity Child via the relation Teacher.teaches_Children.

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COLLECT Child.name FROM ALL Child results in a collection of the values “Kim”, “Rick”, “Bob” and “Mary”

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COLLECT Child FROM Teacher[Teacher_2].teaches_Children results in a collection of the instances Child_1, Child_3 and Child_4

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COLLECT Child.hobbies FROM Teacher[Teacher_1].teaches_Children results in a collection of the values “Reading”, “Dancing”, “Tennis”, “Painting” and “Basketball”

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)

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COLLECT FROM NAMED [WHERE]

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Version of

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COLLECT FROM [WHERE]

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for complex nested selections

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Syntax

Code Block
COLLECT entity \| attribute FROM collection NAMED alias [WHERE expression]

entity or attribute - Entity or attribute to collect. This should contain the alias, e.g. alias.Name.
collection - A collection of entity instances.
alias - A name for the collection.
expression - Boolean expression that represents the criterion the instance has to meet.

Return type

collection of entity instances
collection of attribute values

Examples

Suppose the following model with only instances of entity Person. Person.hasChildren is a relation from Person to Person.

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To retrieve all the parent names, we use this expression:

Code Block
COLLECT Parent.name FROM COLLECT Person FROM ALL Person WHERE (Person.hasChildren != ?) NAMED Parent

This expression results in “Rick”, “Julia” and “Joan”.

To retrieve all children names, we use this expression:

Code Block
COLLECT Child FROM ( COLLECT Person.hasChildren FROM ALL Person WHERE (Person.hasChildren != ?)) NAMED Child

This expression results in a collection of three instances of Person (i.e Person_1, Person_3 and Person_5, with names Kim, Bob and Sam).

To retrieve all children younger than 15, we use this expression:

Code Block
COLLECT Child FROM ( COLLECT Person.hasChildren FROM ALL Person WHERE (Person.hasChildren != ?)) NAMED Child WHERE (Child.Age < 15)

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with

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To retrieve the children’s names with a parent older than 40 years:

Code Block
COLLECT Child.Name FROM ( COLLECT Person.hasChildren FROM ALL Person WHERE (Person.hasChildren != ? AND Person.Age > 40)) NAMED Child

This expression results in a collection with only the name “Kim”.

You can make it as complex as you like, for example:

Code Block
COLLECT Child.Name FROM ( COLLECT Parent.hasChildren FROM ( COLLECT Person FROM ALL Person WHERE (Person.hasChildren != ?)) NAMED Parent WHERE (Parent.Age > 40 ) ) NAMED Child WHERE (Child.Age < 18)

This expression results also in a collection with only the name “Kim”.

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type	note

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an alias

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.

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thisPerson := Person ;
 
COLLECT Person
    FROM ALL Person 
    WHERE (Person != thisPerson)

UNPACK Extracts

UNPACK

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Then:

if Parent_1 is active, SIZE ( Parent.has_Children ) = 3
if Parent_2 is active, SIZE ( Parent.has_Children ) = 1
without an active Parent instance, SIZE ( Parent.has_Children ) results in an error
if Child_1 is active, SIZE ( Child.hobbies ) = 2
if Child_3 is active, SIZE ( Child.hobbies ) = 3
if Child_4 is active, SIZE ( Child.hobbies ) = 1
SIZE ( ? ) = 0

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type	note

COUNT and SIZE are similar except for UNKNOWN: COUNT ( ? ) = UNKNOWN

UNIQUE

The UNIQUE function filters duplicate items from a collection. An expression resulting in a collection, never contains duplicate values. A subexpression however, can contain duplicates.

Syntax

Code Block
UNIQUE ( collection )

collection - A collection of attribute or entity instances.

Examples

Suppose the following model.

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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)

SUBSET OF

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the value from a single valued collection or list.

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Syntax

Code Block
UNPACK collection/list

collection/list - A collection or list of one entity or attribute instance.

Return type

entity instance
attribute value of any type

Examples

Suppose the following data model.

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UNPACK(COLLECT Person.name FROM ALL Person WHERE (Person.SequenceNumber = MIN(COLLECT Person.SequenceNumber FROM ALL Person))) results in “Ron”
In case a second entry "Ron","490" exists, the expression "UNPACK(COLLECT Person.name FROM ALL Person WHERE (Person.SequenceNumber = MIN(COLLECT Person.SequenceNumber FROM ALL Person)))" will fail, because the UNPACK cannot resolve a list with two elements. To solve this the UNIQUE function has to be used: "UNPACK(UNIQUE(COLLECT Person.name FROM ALL Person WHERE (Person.SequenceNumber = MIN(COLLECT Person.SequenceNumber FROM ALL Person))))", which will result in "Ron".
UNPACK(COLLECT Person.name FROM ALL Person WHERE (Person.SequenceNumber = MAX(COLLECT Person.SequenceNumber FROM ALL Person))) results in “Jenny”

SIZE

This function determines the size of a collection.

Syntax

Code Block
SIZE ( collection )

collection - A collection of attribute or entity instances. This can be an expression or a relation attribute for instance.

Return type

integer

Example

Suppose you have a Parent and a Child entity, where Parent has a multivalued relation with Child via the relation Parent.has_Children. With this model the following instances are created:

Is the inverse of the LIST function.
`LIST`	Creates a list based on a value. Is the inverse of the UNPACK function.
`SIZE`	Determines the size of a collection.
`UNIQUE`	Filters duplicate items from a collection resulting from a subexpression in a larger expression.
`SUBSET OF`	Returns

TRUE if the items in a collection are all present in another

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Syntax

Code Block
collection1 SUBSET OF collection2

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collection

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Return type

boolean

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

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type	note

Values between single quotes are considered value list items. For backwards compatibility reasons, a comma separated sequence of value list items is treated as a collection. That's why there is no need to enclose the values between square brackets. In fact if you do add the square brackets you create a matrix rather than a list.

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collection2 - The collection that is tested to hold all the items in the first collection.

UNION Adds two collections of the same base type to a new collection

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Syntax

Code Block
UNION ( collection1 , collection2 )

collection1 - First collection to be added to the new collection.
collection2 - Second collection to be added to the new collection.

Return type

collection

Examples

Suppose you have a Parent and a Child entity, where Parent has a multivalued relation with Child via the relation Parent.has_Children. With this model the following instances are created:

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UNION ( Parent[Parent_1].has_Children , Parent[Parent_2].Has_Children ) results in a collection of all Child instances

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if Child_2 is active, UNION ( Child.hobbies , “Reading” ) = “Tennis”, “Dancing”, “Reading”

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UNION ( Child[Child_1].hobbies , Child[Child_2].hobbies ) = “Reading”, “Dancing”, “Tennis”

INTERSECTION Determines

INTERSECTION

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the intersection of two collections.

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Syntax

Code Block
INTERSECTION ( collection1 , collection2 )

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Return type

collection

Examples

Suppose the following model. Entity Teacher has a multivalued relation with entity Child via the relation Teacher.teaches_Children.


`DIFFERENCE`	Determines the difference between 2 collections. Returns

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INTERSECTION ( Teacher[Teacher_1].teaches_Children , Teacher[Teacher_2].teaches_Children ) results in a collection of Child instances Child_1 and Child_3
INTERSECTION ( Teacher[Teacher_1].teaches_Children.name , Teacher[Teacher_2].teaches_Children.name ) = “Kim”, “Bob”
INTERSECTION ( Child[Child_1].hobbies , Child[Child_3].hobbies ) = “Reading”
INTERSECTION ( Child[Child_2].hobbies , Child[Child_3].hobbies ) results in an empty list

DIFFERENCE

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a collection containing all the items from collection1 that are not present in

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Syntax

Code Block
DIFFERENCE ( collection1 , collection2 )

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collection2

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.

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Return type

collection

Examples

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DIFFERENCE ( [ "nv" , "bv" ] , [ "NV" ] ) = [ "bv" ]

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DIFFERENCE ( 1 , 1 ) results in an empty list

SYMMETRIC_DIFFERENCE

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Determines the symmetric difference between two collections.

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Returns a collection with the elements of the provided collections which are in either one of the collections, but not in both.

A note on collections and duplicates.

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Syntax

Code Block
SYMMETRIC_DIFFERENCE ( collection1 , collection2 )

collection1, collection2 - Collections to be intersected. These collections must be of the same base type.

Return type

collection

Examples

SYMMETRIC_DIFFERENCE ( [ "a", "b", "c"] , [ "c", "d", "e" ] ) = [ "a", "b", "d", "e" ]
SYMMETRIC_DIFFERENCE ( [ "nv" , "bv" ] , [ "NV" ] ) = [ "bv" ]
SYMMETRIC_DIFFERENCE ( 1 , 1 ) results in an empty list

Functions

Include Page

	Collection function EXISTS
	Collection function EXISTS

Include Page

	Collection function EACH
	Collection function EACH

Include Page

	Collection function ALL
	Collection function ALL

Include Page

	Collection function COLLECT FROM WHERE
	Collection function COLLECT FROM WHERE

Include Page

	Collection function COLLECT FROM NAMED WHERE
	Collection function COLLECT FROM NAMED WHERE

Include Page

	Collection function UNPACK
	Collection function UNPACK

Include Page

	Collection function LIST
	Collection function LIST

Include Page

	Collection function SIZE
	Collection function SIZE

Include Page

	Collection function UNIQUE
	Collection function UNIQUE

Include Page

	Collection function SUBSET OF
	Collection function SUBSET OF

Include Page

	Collection function UNION
	Collection function UNION

Include Page

	Collection function INTERSECTION
	Collection function INTERSECTION

Include Page

	Collection function DIFFERENCE
	Collection function DIFFERENCE

Include Page

	Collection function SYMMETRIC_DIFFERENCE
	Collection function SYMMETRIC_DIFFERENCE

Include Page

	A note on collections and duplicates
	A note on collections and duplicates

Collections vs. lists

UNIQUE, SUBSET, UNION and INTERSECTION return a collection of data, i.e. double entries are removed. However, COLLECT statements, + and - return a list of data. You have to be aware of this when using the SIZE or UNPACK function.

Example

Statuses = ["a","b","c","d","a","b","c","d"].

Result

The expression "SIZE ( COLLECT Status FROM {Statuses} )" will result in 8. Note that duplicates are not removed.

The expression "SIZE ( UNIQUE ( COLLECT Status FROM {Statuses} ) )" will result in 4, as the unique filters the duplicates.

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type	warning

When the expression is completely evaluated, all duplicates are filtered as well. Using COLLECT Status FROM {Statuses} as a default expression on an attribute, will result in 4 elements.

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Key

Overview

EXISTS

EACH

ALL

UNPACK

UNIQUE

SUBSET OF

SIZE

INTERSECTION

DIFFERENCE

Functions

Collections vs. lists