Node Visibility

GELLO code will be used to display an ELEMENT node or not. GELLO for node visibility can also be applied for CLUSTERs or data groups. This is important for:

• managing computer screen real estate

• developing 'smart forms' that show and hide nodes depending on value(s) entered elsewhere in the archetype tree

• excluding non-visible nodes from the resulting HL7 message

Apple archetype example

Lets go back to the apple archetype. The example here will add GELLO node visibility to 'Total Cost'. When values have been entered for the higher nodes 'Cost' and 'Number', and the isCalculated attribute GELLO has calculated a value , we may decide its fair enough to make the node visible. Another example where node visibility is useful has been in the pathology domain, where calculation of certain values need only be done and displayed where certain other fields have been entered, eg the calculation of electronic glomerular filtration rate (eGFR).

Open CEN1-Apple.v1.xml again. Set the VisibleAtStart metadata tag for 'Total Cost' on the RHS to false. We will use the isVisible attribute.

Here's a walk through of the GELLO required:

1. Usual beginning - already done:
   
   

   Context CEN_Apple_v1::ArchetypeRoot

2. See if 'Cost' and 'Number' have values. This time we'll just retrieve them as the general type/class Observation:
   
   

   Let cost: Observation = template.Apple.Cost
   Let number: Observation =  template.Apple.Number

3. Set up the test:
    

   let VisA:Boolean =
      if cost.oclIsDefined()
       then 
         If cost.value.oclAsType(PQ).value > 0.0  
          then
           true
          else
        false
      endif
    else
       unknown
    endif

   let VisB:Boolean =
      if number.oclIsDefined()
       then 
         If number.value.oclAsType(Real) > 0.0  
          then
           true
          else
        false
      endif
    else
       unknown
    endif

4. Run the test and return the result (as a boolean):
   
   

    Let result : Boolean =
        If VisA = true and VisB = true then true
            else false
        endif

   result

5. Save your work