Think about a physician who is speaking with a patient about a past event that may have some bearing on their current treatment. The patient knows when and where or possibly who or what was done, and might say something like:
Last year I had surgery for something.
Query: Time of Service AND ((Class = Operative Note) OR (Author Specialty = Surgery) OR (Facility Type = Hospital OR Practice Setting = Surgery)
P: I had something like this two years ago, and I saw Dr. Smith.
Query: Time of Service AND Author = Dr. Smith
P: The cardiologist at St. Mary's told me I had ...
Query: Author Institution = St. Mary's AND Author Specialty = Cardiology
P: I did this test a year ago at ____, and when my doc looked at the result, he told me not to worry about it.
Query: Type Code ~ Test and Time of Service and Author Institution
D: We need to look at the original x-rays showing the placement of your pacemaker.
P: Oh, Dr. Smith did that, but I cannot remember when. It might have been in ... or was it...
Query: Author = Dr. Smith AND Author Specialty = Cardiology
P: Oh, I had that done at ___ hospital.
Query: Organization AND Author Specialty = Cardiology
Query: Time of Service AND Author Specialty = Cardiology
D: We would like to talk to his cardiologist ...
Son: I don't know who that is.
Query: Author Specialty = Cardiology
D: What else happened during that stay?
P: I don't really remember. I know I had a bunch of tests to rules out something or other, but I don't remember what it was or what they were.
Query: FindSubmissionSets with Submission Time
P: They drew blood if that helps.
Query: Practice Setting = Laboratory
And me, with my Claims Attachments hat on at the time (remember, back then the NPRM was only a couple of years late)
Insurer: Send me all documents for the current stay.
Query: Author Institution and Time of Service
Insurer: Send me all labs for the last 30 days
Query: Practice Setting = Laboratory and Time of Service
And so on. These were the kinds of questions that led to the creation of the XDS Metadata way back when. Fortunately, we also had several good lists of Metadata to rely upon as well, including CDA Release 1, CDA Release 2, an early edition of CCR, DICOM, and CEN 13606. What was chosen was a superset of metadata from those specifications that would allow answers to the questions above. There is other metadata that is in there for other purposes, but these were the kinds of queries we were thinking about.