Other functions [9.6] replaces More functions

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.

• for Bob, ISNULL ( Person.SequenceNumber ) = FALSE
• for Jane, ISNULL ( Person.SequenceNumber ) = TRUE

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.

• for Jane, ISUNKNOWN ( Person.SequenceNumber , 999 ) = 999
• for Mary, ISUNKNOWN ( Person.SequenceNumber , 999 ) = 667

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” ) )

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 Kitchen instance the expression TYPE OF Room = “Kitchen”
• for the Bedroom instances the expression TYPE OF Room = “Bedroom” = TRUE