Collection functions

This function determines whether an instance of a specified entity exists, optionally meeting certain criteria.

Syntax

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.

• EXISTS Person = TRUE
• EXISTS Person WHERE ( Person.age < 18 ) = FALSE
• EXISTS Person WHERE ( Person.gender = “m” AND Person.age > 35 ) = TRUE

Use this function to create a collection of all instances of a specified entity.

Syntax

 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.

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

Use this function to create a collection of entity or attribute instances (meeting certain criteria).

Syntax

 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.

• COLLECT Child.name FROM ALL Child =  [ “Kim”, “Rick”, “Bob”, “Mary” ]
• COLLECT Child FROM Teacher[Teacher_2].teaches_Children  = [ Child_1, Child_3, Child_4 ]
• COLLECT Child.hobbies FROM Teacher[Teacher_1].teaches_Children =  [ “Reading”, “Dancing”, “Tennis”, “Painting”, “Basketball” ]
• COLLECT Child.name FROM ALL Child WHERE ( Child.hobbies = “Reading” ) = [ “Kim”, “Bob” ]
• COLLECT Child.hobbies FROM ALL Child WHERE ( Child.name = “Mary” ) = [ “Football” ]

Use this version of the COLLECT FROM [WHERE] function for complex nested selections in which it is necessary to use an alias.

Syntax

 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.

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

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:

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:

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

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

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

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:

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”.

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

Use this function to extract the value from a single valued collection or list.

Syntax

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.

• UNPACK ( COLLECT Person.name FROM ALL Person WHERE ( Person.SequenceNumber = MIN ( COLLECT Person.SequenceNumber FROM ALL Person ) ) ) = “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 ) ) ) ) = "Ron".
• UNPACK ( COLLECT Person.name FROM ALL Person WHERE ( Person.SequenceNumber = MAX ( COLLECT Person.SequenceNumber FROM ALL Person ) ) ) = “Jenny”

This function determines the size of a collection.

Syntax

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:

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

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

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

Syntax

 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

Diagram

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:

• UNION ( Parent[Parent_1].has_Children , Parent[Parent_2].Has_Children ) results in a collection of all Child instances
• UNION ( Parent[Parent_1].has_Children.name , Parent[Parent_2].Has_Children.name ) = “Kim”, “Rick”, “Bob”, “Mary”
• if Child_2 is active, UNION ( Child.hobbies , “Reading” ) = “Tennis”, “Dancing”, “Reading”
• UNION ( Child[Child_1].hobbies , Child[Child_2].hobbies ) = “Reading”, “Dancing”, “Tennis”

This function determines the intersection of two collections. It returns a collection containing the items that are present in both specified collections.

Syntax

INTERSECTION ( collection1 , collection2 )

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

Return type

• collection

Diagram

Examples

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

• 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