Table 1.

The four layers in the knowledge representation framework

	Narrative	Semi-structured	Structured	Executable
Format	Narrative text	Organized text	Coded and interpretable by computer	Coded and interpretable by CDS systems; variety of formats
Sharability of knowledge	Broad	Broad	Broad	Very limited
CDS modality and tool independent	Yes	Yes	Yes	No
Site independent	Yes	Yes	Yes	No
Author	Guideline developer	Clinical domain expert	Knowledge engineer	CDS implementer
Purpose	Communication of policy; synthesis of evidence	Recommendations for implementation in CDS	Precise communication; validation	Implementation for a particular site

CDS, clinical decision support.