It doesn't really make sense to have logic rules be stored as "derived concepts". Concepts are generally questions and answers for observations. Rules are something different. Also, tokens and their attached rules are our mechanism for accessing the whole data model for a patient. If you want to define "Is asthmatic?" as a rule, that should be bound directly to a token. You shouldn't have to create an "IS ASTHMATIC?" concept, and have that bound to a token via reference rule.
So, the thing formerly implemented as a concept of datatype=Derived (which has been committed to trunk, but is not in any released version of the code) is going to be pulled out. The implementation will remain exactly the same, but it will be called a LogicRule instead of a ConceptDerived.