Enable When / Display When rules

[xamelon]

Description

Form is a list of questions grouped together around specific problem.
Form is used to capture data from respondents (patients,practitioners, etc...)

In some forms we want to have a logic that hides or shows particular fields in some cases.

Use cases

• In patient screening form I want to show questions about pregnancy/breastfeeding only to women
• In PHQ2/PHQ9 combined form, I want to show PHQ9 form if PHQ2 screening was positive

Questions

• How complex logic do I need in enable when/display when rules?
• How to build this rules from UI builder?
• What is simplier for form developers?

Approaches

• FHIR way to build rules as constructor
• fhirpath
• Aidbox Zen Lisp

To compare these 3 approaches we will describe the same rules:

Display an item when answer to gender question is female

Display an email field when answer contact checkbox is checked
and answer to contact-type is email

[xamelon]

Rules Constructor (FHIR way)

Single rule is a map of question, operator, and value to be compare with.
Behaviour can be described via several rules.

{:display-when [{:question :gender
                 :operator :=
                 :value {:code "female"
                         :display "Female"}}]}

To refer on multiple fields in logic we need to state several rules.

{:display-when [{:question :contact
                 :operator :=
                 :value true}
                {:question :contact-type
                 :operator :=
                 :value "email"}]
 :display-when-behaviour :all}

This approach is easy to understand to every user, also this kind of rules can be easily created via UI builder

But, we can't describe complex rules (cond1 and cond2 or cond3 and cond4)

[xamelon]

FHIR Path

Rule is fhirpath expression: http://hl7.org/fhirpath/
Fhirpath is widely used in FHIR and familiar for developers.

items.where(id = 'gender').first().value.code = 'female'

OR

gender.value.code = 'female'

We can easily write a rule that relies on multiple fields

contact.value = true and contact-type.value.code = 'email'

Also, we can write complex rules:

contact.value = true and contact-type.value.code = 'phone'
or
contact.value = true and contact-type.value.code = 'fax'

[xamelon]

Aidbox Zen Lisp

This is current solution in Aidbox SDC Docs link

➕ We control it and can extend it as we want.
➕ Using lisp we can describe a rule of any complexity
➖ Familiar only for Health Samurai team.

(= (get-in [:gender :value]) "female")

(and
 (= (get-in [:contact :value]) true)
 (= (get-in [:contact-type :value :code] "email")))

(or
 (and (= (get-in [:contact :value]) true)
      (= (get-in [:contact-type :value :code]) "phone"))
 (and (= (get-in [:contact :value]) true)
      (= (get-in [:contact-type :value :code]) "fax")))