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UNIQUE
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 )
Input
- collection - A collection of attribute or entity instances.
Return type
- collection
Examples
Suppose the following model.
| Person instance | Person.name |
|---|---|
| Person_1 | “Kim” |
| Person_2 | “Rick” |
| Person_3 | “Bob” |
| Person_4 | “Rick” |
| Expression | Result | Type | Note |
|---|---|---|---|
| COLLECT Person.name FROM ALL Person | [ "Kim" , "Rick" , "Bob" ] | String (multivalued) | A result never contains duplicate values |
| SIZE ( COLLECT Person.name FROM ALL Person ) | 4 | Integer | A subexpression can contain duplicate values |
| SIZE ( UNIQUE ( COLLECT Person.name FROM ALL Person ) ) | 3 | Integer | 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
collection1 SUBSET OF collection2
Inputs
- 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
Venn diagram
Examples
| Expression | Result | Type | Note |
|---|---|---|---|
| ( 'a' , 'b' , 'c' ) SUBSET OF ( 'a' , 'b' , 'c' , 'd' ) | TRUE | Boolean | |
| ( 'a' , 'b' , 'c' , 'd' ) SUBSET OF ( 'a' , 'b' , 'c' ) | FALSE | Boolean | |
| Person.hobbies SUBSET OF [ "Tennis" , "Soccer" , "Music" ] Given Person.hobbies = [ "Tennis" , "Soccer" ] | TRUE | Boolean | |
| Person.hobbies SUBSET OF [ "Tennis" , "Soccer" , "Music" ] Given Person.hobbies = [ ? ] | ? | Boolean | |
| Person.hobbies SUBSET OF [ "Tennis" , "Soccer" , ? ] Given Person.hobbies = [ "Tennis" , "Soccer" ] | FALSE | Boolean | [ "Tennis" , "Soccer" , ? ] evaluates to [ ? ] Person.hobbies SUBSET OF [ ? ] = FALSE |
| ( 'a' , 'b' , 'c' ) SUBSET OF ( [ 'a' , 'b' , 'c' , 'd' ] ) | Error | ||
1 SUBSET OF Address.Numbers Given Adress.Numbers = ? | FALSE | Boolean |
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
UNION ( collection1 , collection2 )
Inputs
- collection1 - First collection to be added to the new collection.
- collection2 - Second collection to be added to the new collection.
Return type
- collection
Venn 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:
| 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” |
| Expression | Result | Type |
|---|---|---|
| UNION ( Parent[Parent_1].has_Children , Parent[Parent_2].Has_Children ) | [ Child_1, Child_2 , Child_3, Child_4 ] | Collection of Child instances |
| UNION ( Parent[Parent_1].has_Children.name , Parent[Parent_2].Has_Children.name ) | [ “Kim”, “Rick”, “Bob”, “Mary” ] | String (multivalued) |
| UNION ( Child[Child_2].hobbies , "Reading" ) | [ “Tennis”, “Dancing”, “Reading” ] | String (multivalued) |
| UNION ( Child[Child_1].hobbies , Child[Child_2].hobbies ) | [ “Reading”, “Dancing”, “Tennis” ] | String (multivalued) |
| UNION( ?, [1, 2] ) | UNKNOWN | Integer (multivalued) |
INTERSECTION
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 )
Inputs
- collection1, collection2 - Collections to be intersected. These collections must be of the same base type.
Return type
- collection
Venn diagram
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” |
| Expression | Result | Type |
|---|---|---|
| INTERSECTION ( Teacher[Teacher_1].teaches_Children , Teacher[Teacher_2].teaches_Children ) | [ Child_1 , Child_3 ] | Collection of Child instances |
| INTERSECTION ( Teacher[Teacher_1].teaches_Children.name , Teacher[Teacher_2].teaches_Children.name ) | [ "Kim" , "Bob" ] | String (multivalued) |
| INTERSECTION ( Child[Child_1].hobbies , Child[Child_3].hobbies ) | [ "Reading" ] | String (multivalued) |
| INTERSECTION ( Child[Child_2].hobbies , Child[Child_3].hobbies ) | [ ] | String (multivalued) |
| INTERSECTION( ?, [ 1, 2 ] ) | UNKNOWN | Integer (multivalued) |
DIFFERENCE
This function returns a collection containing all the items from collection1 that are not present in collection2.
Syntax
DIFFERENCE ( collection1 , collection2 )
Inputs
- collection1, collection2 - Collections to be compared. These collections must be of the same base type.
Return type
- collection
Venn diagram
Examples
| Expression | Result | Type |
|---|---|---|
| DIFFERENCE ( [ "a", "b", "c"] , [ "c", "d", "e" ] ) | [ "a" , "b" ] | String (multivalued) |
| DIFFERENCE ( [ "nv" , "bv" ] , [ "NV" ] ) | [ "bv" ] | String (multivalued) |
| DIFFERENCE ( 1 , 1 ) | [ ] | Integer (multivalued) |
| DIFFERENCE( [ 1, 2 ], ? ) | ? | Integer (multivalued) |
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
SYMMETRIC_DIFFERENCE ( collection1 , collection2 )
Inputs
- collection1, collection2 - Collections to be compared. These collections must be of the same base type.
Return type
- collection
Venn diagram
Examples
| Expression | Result | Type |
|---|---|---|
| SYMMETRIC_DIFFERENCE ( [ "a" , "b" , "c" ] , [ "c" , "d" , "e" ] ) | [ "a", "b", "d", "e" ] | String (multivalued) |
| SYMMETRIC_DIFFERENCE ( [ "nv" , "bv" ] , [ "NV" ] ) | [ "bv" ] | String (multivalued) |
| SYMMETRIC_DIFFERENCE ( 1 , 1 ) | [ ] | Integer (multivalued) |
A note on collections and duplicates
An expression resulting in a collection does not contain duplicates. Please be aware however, that intermediary results of a COLLECT statement can contain duplicates. You have to be aware of this when using the SIZE or UNPACK function, or when using TSL.
This is best illustrated with the following examples.
| Person instance | Person.Name | Person.Age |
|---|---|---|
| Person_1 | Kim | 24 |
| Person_2 | Rick | 25 |
| Person_3 | Bob | 25 |
| Expression | Result | Type | Note |
|---|---|---|---|
| COLLECT Person.Age FROM ALL Person | [ 24 , 25 ] | String (multivalued) | |
| SIZE ( COLLECT Person.Age FROM ALL Person ) | 3 | Integer | The intermediary collection is [ 24, 25, 25 ] |
TSL: The ages present are: [[[ COLLECT Person.Age FROM ALL Person ]]]. | The ages present are: 24, 25, 25. | String | The intermediary collection is [ 24, 25, 25 ] |
| SIZE ( UNIQUE ( COLLECT Person.Age FROM ALL Person ) ) | 2 | Integer | The duplicates in the intermediary collection are filtered by the UNIQUE function |
Now an example with the UNPACK function. We leave out the first instance from the previous example.
| Person instance | Person.Name | Person.Age |
|---|---|---|
| Person_2 | Rick | 25 |
| Person_3 | Bob | 25 |
| Expression | Result | Type | Note |
|---|---|---|---|
| COLLECT Person.Age FROM ALL Person | [ 25 ] | Integer (multivalued) | |
| UNPACK ( COLLECT Person.Age FROM ALL Person ) | Error | The collection contains 2 elements [ 25 , 25 ] | |
| UNPACK ( UNIQUE ( COLLECT Person.Age FROM ALL Person ) ) | 25 |
Only the intermediary results of a COLLECT statement can contain duplicates. The functions UNIQUE, UNION, INTERSECTION, DIFFERENCE and SYMMETRIC_DIFFERENCE always return collections without duplicates.
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