Source:http://linkedlifedata.com/resource/umls/id/C1555707
HL7V3.0: <p>This context represents the part of a patient record conveyed in a single communication. It is drawn from a providing system for the purposes of communication to a requesting process (which might be another repository, a client application or a middleware service such as an electronic guideline engine), and supporting the faithful inclusion of the communicated data in the receiving system.</p><p>An extract may be the entirety of the patient record as held by the sender or it may be a part of that record (e.g. changes since a specified date).</p><p>An extract contains folders or compositions.</p><p>An extract cannot contain another extract.</p>