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For instance, if the patient's electronic health record indicates that the patient had the procedure "Tonsillectomy with adenoidectomydiagnosis "Acute tonsillitis," then that fact needs to be recorded in the CRC database using the standard code for that particular procedure diagnosis as defined in the ONT database. In the case of using the default i2b2 Procedures Diagnoses metadata tree, that code would be "ICD9:28.3463". When a researcher makes a query in the user interface for "Tonsillectomy with adenoidectomyAcute tonsillitis," then i2b2 will query the CRC database for all patients who have the code ICD9:28.3463 in their data records.

Let's view a high-level illustration of the mechanism behind a typical query. Here's that concept's definition from the procedures diagnoses table in the ONT (metadata) database:

When the user selects that Concept Name in the user interface, the i2b2 Query Tool associates that with the Concept Path. When running the query, i2b2 looks for that path in the concepts table in the CRC database, which looks like this...

...and i2b2 associates that Concept Path with the Concept Code for that concept. i2b2 then locates those patients in the facts table in the CRC database that share that Concept Code...

... and reports a count of those patients back to the user at the conclusion of the query. In this illustration, there were 3 2 patients (over 6 encounters) that had this Concept Code in the facts table, so the user's query for patients with the "Tonsillectomy with adenoidectomy" procedure a diagnosis of "Acute tonsillitis" will return a count of 3 2 patients.

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