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SCHEMA MyExpressSchema;
	ENTITY MyEntity;
		attr1 : STRING;
	END_ENTITY;
END_SCHEMA;

TRIGGER_SCHEMA MyTriggerSchema FOR MyExpressSchema;
	DECLARE target_model INSTANCE OF MyExpressSchema;

---------------------------------------------------------------------------
-- the system recognized events is proposed to define as INTEGER XPX pseudo constants
-- then we can expand range of trigger events without enhancing grammar 
-- declaration can be assumed as something like:
---------------------------------------------------------------------------
trigger_source = ENUMERATION OF(
		XPX_Create_Entity,		-- raised after entity is created
		XPX_Delete_Entity,		-- raised before an entity is deleted
		XPX_Read_Entity,		-- any attribute is accessed
		XPX_Write_Entity,		-- any attribute is modified

		XPX_Pre_Set_Attribute,		-- raised before specified attribute is assigned (do we need PRE/POST?)
		XPX_Post_Set_Attribute,		-- raised after specified attribute is assigned (do we need PRE/POST?)
		XPX_Pre_Unset_Attribute,	-- raised before an attribute is set to UNSET
		XPX_Post_Unset_Attribute,	-- raised after an attribute is set to UNSET
		XPX_Read_Attribute,			-- any attribute is accessed

		XPX_Create_Model,		-- raised after model is created
		XPX_Delete_Model,		-- raised before model is deleted
		XPX_Read_Model,			-- raised if any data in model accessed (pre)
		XPX_Write_Model,		-- raised if any data in model written (pre)

		XPX_Commit_Write_Transaction,		-- raised just before write transaction committed (what about tx levels?)
		XPX_Abort_Write_Transaction,		-- raised just before write transaction aborted(what about tx levels?)

	);

---------------------------------------------------------------------------
-- we use the DECLARE keyword to connect events to handlers 
-- Pattern: DECLARE trigger_function TRIGGER_FUNCTION(trigger_source) FOR (target);
---------------------------------------------------------------------------	
	DECLARE EntityTrigger 		TRIGGER_FUNCTION(XPX_Create_Entity) 	FOR MyEntity;
	DECLARE AttributeTrigger 	TRIGGER_FUNCTION(XPX_Pre_SetAttribute) 	FOR MyEntity.MyAttribute;
	DECLARE ModelTrigger 		TRIGGER_FUNCTION(XPX_Create_Model) 		FOR target_model;

	
	TRIGGER_FUNCTION EntityTrigger(theEntity: GENERIC_ENTITY) : GENERIC;
		RETURN(?);
	END_TRIGGER_FUNCTION;

	TRIGGER_FUNCTION AttributeTrigger(theEntity: GENERIC_ENTITY) : GENERIC; -- look in DECLARE TRIGGER declarartion to identify attribute
		RETURN(?);
	END_TRIGGER_FUNCTION;

	TRIGGER_FUNCTION ModelTrigger(theModel: GENERIC_ENTITY) : GENERIC; -- theModel will refer to SDAI_MODEL instance
		RETURN(?);
	END_TRIGGER_FUNCTION;
	
	
---------------------------------------------------------------------------
-- so for possibility to user defined events
-- firstly the events need to be enumerated somehow. Not trivial as they are cross-schema and cross-model
-- could be kept in a trigger schema, meaning both raise and catch must be done within that schema.
-- anyway, if identified as integer constants we may declare them as such:
---------------------------------------------------------------------------	
	CONSTANT
		somethingCreatedEvent : INTEGER := 1001;
		somethingDeletedEvent : INTEGER := 1002;
	END_CONSTANT;
	
-- to raise events - easy way out is to use same technique as for XPX exception:		
	PROCEDURE ThrowAnEvent(arg : GENERIC);
		xpxRaiseEvent(eventType,eventTarget,.....);
	EBD_PROCEDURE;
	

-- to catch events is like catching trigger events, so we use same declaration
-- Pattern: DECLARE eventHandler TRIGGER(eventType) FOR target; -- target is a model I think...
	
	DECLARE EventHandler TRIGGER_FUNCTION(somethingCreatedEvent) FOR target_model;
	DECLARE EventHandler TRIGGER_FUNCTION(somethingDeletedEvent) FOR target_model;
	
	TRIGGER_FUNCTION EventHandler(event : GENERIC_ENTITY) : GENERIC;
	LOCAL
		myEventType : INTEGER;
	END_LOCAL;
		myEventType := event.eventType;
		RETURN(?);	
	END_TRIGGER_FUNCTION;
	
END_TRIGGER_SCHEMA;

ENTITY xIfcWorkTask SUBTYPE OF(IfcTask);    
    subTaskOf : xIfcWorkTask;
    dependentOn : SET[0:*] OF xIfcWorkTask;
END_ENTITY;