Property expression : Iv3ED; (Read/Write)
An expression that can be used to derive the actual value of the quantity given information taken from the context of use.
For example expression can be used for expressing dosage instructions that depend on patient body weight.
If no proper value is provided for the QTY, then the value SHALL have a nullFlavor, whether or not an expression is provided. If no proper value is provided, and an expression is provided, the appropriate nullFlavor is usually DER. No nullFlavor is required if both a proper value and an expression is provided; in such cases, it is up to the processing to determine when the expression should be evaluated.
The language of the expression is inferred from the mediatype. If multiple translations are provided in the expression, the evaluator is free to choose whichever language is preferred; all translations SHALL specify the same outcome.
The language defines the forms that the expression property can take, how the information available in the context of the expression is made available within the features of the language, and how the language declares the new form of the value. Languages may only be used if this information has been appropriately defined for the context in which the QTY is used.
Information Processing Entities are not required to implement any languages in order to claim direct or indirect conformance to this specification, but SHOULD declare what languages are supported in their conformance statements.
Note: Factor is an HL7 specific language documented in the Abstract Data Types Specification.