Sets the value of Expression attribute. This attribute represents the expression used to store additional information for the property template depending on the PropertyType. It should the following definitions, if the PropertyType is set to:

• kIfcSimplePropertyTemplateTypeEnum_P_TABLEVALUE: the expression that could be evaluated to define the correlation between the defining values and the defined values.
• kIfcSimplePropertyTemplateTypeEnum_Q_LENGTH, kIfcSimplePropertyTemplateTypeEnum_Q_AREA, kIfcSimplePropertyTemplateTypeEnum_Q_VOLUME, kIfcSimplePropertyTemplateTypeEnum_Q_COUNT, kIfcSimplePropertyTemplateTypeEnum_Q_WEIGHT, kIfcSimplePropertyTemplateTypeEnum_Q_TIME: the formula to be used to calculate the quantity.

No value shall be asserted if the PropertyType is not listed above.