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EXISTS
This function determines whether an instance of a specified entity exists meeting certain criteria.
Syntax
Code Block |
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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.
Person.name | Person.gender | Person.age |
---|---|---|
“Kim” | “f” | 23 |
“Rick” | “m” | 35 |
“Bob” | “m” | 42 |
“John” | “m” | 19 |
“Mary” | “f” | 33 |
- EXISTS Person returns TRUE
- EXISTS Person WHERE (Person.age < 18) returns FALSE
- EXISTS Person WHERE (Person.gender = “m” AND Person.age > 35) returns TRUE
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The return value of a boolean can be TRUE, FALSE or UNKONWN. |
EACH
This function determines whether all instances of a specified entity meet a certain criteria
Syntax
Code Block |
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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
Suppose the following data model.
Person.name | Person.gender | Person.age |
---|---|---|
“Kim” | “f” | 23 |
“Rick” | “m” | 35 |
“Bob” | “m” | 42 |
“John” | “m” | 19 |
“Mary” | “f” | 33 |
- EACH Person WHERE (Person.age < 18) returns FALSE
- EACH Person WHERE (Person.age > 18) returns TRUE
- EACH Person WHERE (Person.age < 20) returns FALSE
- EACH Person WHERE (Person.gender = “m” OR Person.age > 35) returns FALSE
- EACH Person WHERE (Person.gender = “m” OR Person.age > 20) returns TRUE
ALL
Use this function to create a collection of all instances of a specified entity.
Syntax
Code Block |
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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.
Parent instance | Child instance |
---|---|
Parent_1 | Child_1 |
Parent_1 | Child_2 |
Parent_1 | Child_3 |
Parent_2 | Child_4 |
- ALL Parent returns a collection of Parent_1 and Parent_2
- ALL Child returns a collection of Child_1, Child_2, Child_3 and Child_4
- ALL Person returns a collection of Parent_1, Parent_2, Child_1, Child_2, Child_3 and Child_4
COLLECT FROM [WHERE]
Use this function to create a collection of entity or attribute instances (meeting certain criteria).
Syntax
Code Block |
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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.
Teacher instance | Child instance | Child.name | Child.hobbies |
---|---|---|---|
Teacher_1 | Child_1 | “Kim” | “Reading”, “Dancing” |
Teacher_1 | Child_2 | “Rick” | “Tennis”, “Dancing” |
Teacher_1 | Child_3 | “Bob” | “Painting”, “Basketball”, “Reading” |
Teacher_2 | Child_1 | “Kim” | “Reading”, “Dancing” |
Teacher_2 | Child_3 | “Bob” | “Painting”, “Basketball”, “Reading” |
Teacher_2 | Child_4 | “Mary” | “Football” |
- COLLECT Child.name FROM ALL Child results in a collection of the values “Kim”, “Rick”, “Bob” and “Mary”
- COLLECT Child FROM Teacher[Teacher_2].teaches_Children results in a collection of the instances Child_1, Child_3 and Child_4
- COLLECT Child.hobbies FROM Teacher[Teacher_1].teaches_Children results in a collection of the values “Reading”, “Dancing”, “Tennis”, “Painting” and “Basketball”
- COLLECT Child.name FROM ALL Child WHERE (Child.hobbies = “Reading”) results in a collection of the values “Kim” and “Bob”
- COLLECT Child.hobbies FROM ALL Child WHERE (Child.name = “Mary”) results in a collection of the value “Football”
COLLECT FROM NAMED [WHERE]
Use this version of the COLLECT FROM [WHERE] function for complex nested selections in which it is necessary to use an alias.
Syntax
Code Block |
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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.
Person instance | Person.Name | Person.Age | Person.hasChildren |
---|---|---|---|
Person_1 | “Kim” | 16 | |
Person_2 | “Rick” | 38 | Person_3, Person_5 |
Person_3 | “Bob” | 8 | |
Person_4 | “Julia” | 42 | Person_1 |
Person_5 | “Sam” | 3 | |
Person_6 | “Joan” | 34 | Person_3, Person_5 |
To retrieve all the parent names, we use this expression:
Code Block |
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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 |
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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 |
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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:
Code Block |
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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 |
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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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In some occasions, a local variable could be a good alternative for using an alias. E.g. if you want a collection of all persons except the person that is currently active, this would be simple and transparent:
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UNPACK
Use this function to extract the value from a single valued collection or list.
Syntax
Code Block |
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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.
Person.name | Person.SequenceNumber |
---|---|
“Bob” | 654 |
“Jane” | 523 |
“Mary” | 667 |
“Rick” | 500 |
“Ron” | 490 |
“Jenny” | 765 |
- 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 |
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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:
Parent instance | Child instance | Child.name | Child.hobbies |
---|---|---|---|
Parent_1 | Child_1 | “Kim” | “Reading”, “Dancing” |
Parent_1 | Child_2 | “Rick” | “Tennis”, “Dancing” |
Parent_1 | Child_3 | “Bob” | “Painting”, “Basketball”, “Reading” |
Parent_2 | Child_4 | “Mary” | “Football” |
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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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 |
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UNIQUE ( collection ) |
- collection - A collection of attribute or entity instances.
Examples
Suppose the following model.
Person instance | Person.name |
---|---|
Person_1 | “Kim” |
Person_2 | “Rick” |
Person_3 | “Bob” |
Person_4 | “Rick” |
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
This function returns TRUE
if the items in a collection are all present in another collection.
Syntax
Code Block |
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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
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 ifPerson.hobbies = “Tennis”, “Soccer”
(Person.hobbies) SUBSET OF ([“Tennis”, “Soccer”, “Music”])
= UNKNOWNif Person.hobbies = ?
(Person.hobbies) SUBSET OF ([“Tennis”, “Soccer”, ?])
= FALSE ifPerson.hobbies = “Tennis”, “Soccer”
('a', 'b', 'c') SUBSET OF (['a', 'b', 'c'])
will result in an error.
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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. |
UNION
Adds two collections of the same base type to a new collection.
Syntax
Code Block |
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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:
Parent instance | Child instance | Child.name | Child.hobbies |
---|---|---|---|
Parent_1 | Child_1 | “Kim” | “Reading”, “Dancing” |
Parent_1 | Child_2 | “Rick” | “Tennis”, “Dancing” |
Parent_1 | Child_3 | “Bob” | “Painting”, “Basketball”, “Reading” |
Parent_2 | Child_4 | “Mary” | “Football” |
UNION ( Parent[Parent_1].has_Children , Parent[Parent_2].Has_Children )
results in a collection of allChild
instancesUNION ( 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”
INTERSECTION
This function determines the intersection of two collections. It returns a collection containing the items that are present in both specified collections.
Syntax
Code Block |
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INTERSECTION ( collection1 , collection2 ) |
- collection1, collection2 - Collections to be intersected. These collections must be of the same base type.
Return type
- collection
Examples
Suppose the following model. Entity Teacher
has a multivalued relation with entity Child
via the relation Teacher.teaches_Children
.
Teacher instance | Child instance | Child.name | Child.hobbies |
---|---|---|---|
Teacher_1 | Child_1 | “Kim” | “Reading”, “Dancing” |
Teacher_1 | Child_2 | “Rick” | “Tennis”, “Dancing” |
Teacher_1 | Child_3 | “Bob” | “Painting”, “Basketball”, “Reading” |
Teacher_2 | Child_1 | “Kim” | “Reading”, “Dancing” |
Teacher_2 | Child_3 | “Bob” | “Painting”, “Basketball”, “Reading” |
Teacher_2 | Child_4 | “Mary” | “Football” |
INTERSECTION ( Teacher[Teacher_1].teaches_Children , Teacher[Teacher_2].teaches_Children )
results in a collection ofChild
instancesChild_1
andChild_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
This function returns a collection containing all the items from collection1 that are not present in collection 2.
Syntax
Code Block |
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DIFFERENCE ( collection1 , collection2 ) |
- collection1, collection2 - Collections to be intersected. These collections must be of the same base type.
Return type
- collection
Examples
DIFFERENCE ( [ "a", "b", "c"] , [ "c", "d", "e" ] )
= [ "a" , "b" ]DIFFERENCE ( [ "nv" , "bv" ] , [ "NV" ] )
= [ "bv" ]DIFFERENCE ( 1 , 1 )
results in an empty list
SYMMETRIC_DIFFERENCE
This function determines the symmetric difference between two collections. It returns a collection with the elements of the provided collections which are in either one of the collections, but not in both.
Syntax
Code Block |
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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
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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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. |