title: HL7 OIDs and FHIR URIs
body: <p>I am new to the Health Level 7 standards and messaging paradigm and was reading up on OIDS/URIs. While I know OID are unique Identifiers assigned under an Assigning Authority, I would like to know the following:</p>
  
  <ol>
  <li>If there any difference in their usage for V2 and V3 messages.  </li>
  <li>Whatis actually sent over the wire in terms of an OID?  </li>
  <li>Why is there a
  switch from OIDs to URIs in the context of the new HL7 FHIR standard?</li>
  </ol>
  
  <p>Any help is appreciated.</p>
  
  <p>Thanks</p>