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ISNULL
This function checks whether a value is unknown
Syntax
ISNULL(expression)
- expression - Expression that is checked.
Return type
- boolean - TRUE of the attribute is unknown, FALSE otherwise
Examples
Suppose the following data model.
| Person.name | Person.SequenceNumber |
|---|---|
| “Bob” | 654 |
| “Jane” | ? |
- for Bob,
ISNULL ( Person.SequenceNumber )= FALSE - for Jane,
ISNULL ( Person.SequenceNumber )= TRUE
ISUNKNOWN
This function replaces a value if that value is unknown.
Syntax
ISUNKNOWN(expression, value)
- expression- Expression of which the value has to be returned if that value is known.
- value - Value to return if the attribute value is unknown.
Return type
- any type, equals the attribute type
Examples
Suppose the following data model.
| Person.name | Person.SequenceNumber |
|---|---|
| “Bob” | 654 |
| “Jane” | ? |
| “Mary” | 667 |
| “Rick” | ? |
| “Ron” | ? |
| “Jenny” | 765 |
- for Jane,
ISUNKNOWN ( Person.SequenceNumber , 999 )= 999 - for Mary,
ISUNKNOWN ( Person.SequenceNumber , 999 )= 667
IS A
Use this function to check the type of an instance. The function returns TRUE if the selected instance is of the specified entity.
Syntax
instance IS A entity_name
- instance - Instance to check.
- entity_name - Name of the entity as string.
Return type
- boolean
Examples
Suppose a domain model in which there is a singleton entity Residence that has a multivalued relation hasRooms with Room. Room is the base entity for singleton Kitchen and not singletons Bedroom and Bathroom.
If you want to determine the number of bedrooms is the residence:
COUNT ( COLLECT Room FROM Residence.hasRooms WHERE ( Room IS A “Bedroom” ) )
If you want to determine the number of bathrooms is the residence:
COUNT ( COLLECT Room FROM Residence.hasRooms WHERE ( Room IS A “Bathroom” ) )
TYPE OF
Use this function to determine the type of an instance. The function returns the name of the entity.
Syntax
TYPE OF base_entity
- base_entity - Name of the instance's base entity.
Return type
- string
Examples
Suppose a domain model in which there is a singleton entity Residence that has a multivalued relation hasRooms with Room. Room is the base entity for singleton Kitchen and not singletons Bedroom and Bathroom.
- for the
Kitcheninstance the expressionTYPE OF Room= “Kitchen” - for the
Bedroominstances the expressionTYPE OF Room = “Bedroom”= TRUE
ISACTIVE
Use this function to determine if an instance of a specific type is currently active.
ISACTIVE instances [WHERE condition]
- instances - instances to search
- condition - optional condition to limit the collection of instances to check
Return type
boolean - TRUE if one of the instances is active, FALSE otherwise
Singletons are always active, so ISACTIVE <singleton> will always return TRUE
Examples
Suppose the following data model.
| instance_id | Person.name | Person.Age |
|---|---|---|
| Person_1 | “Bob” | 14 |
| Person_2 | “Jane” | 25 |
| Person_3 | “Mary” | 30 |
- If no instance of Person is activated,
ISACTIVE Person= FALSE - If
Person_1is active,ISACTIVE Person= TRUE - If
Person_1is active,ISACTIVE Person WHERE Person.Age >= 18= FALSE (sincePerson_1is excluded by the condition) ISACTIVE system= TRUE (systemcontains the system attributes and is a singleton. Therefore it is always active)- If no instance of Person is activated, the following expression will fail because Person is not in scope:
Person.Name >= 18
ISACTIVEfunction the expression can be evaluated without error:(ISACTIVE Person) AND Person.name >= 18Note that expression above will be evaluated from left to right, so first (ISACTIVE Person) will be evaluated (= FALSE) and therefore the result of the AND will be FALSE as well. The right hand side of the expression (Person.Name >= 18) will not be evaluated,
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