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The i2b2 metadata in the ONT database work together with the patient data in the CRC database. Each patient "observation" in the CRC database must have a code associated with it, and that code must match a healthcare concept — diagnosis, procedure, medication, lab test, demographic descriptor, etc. — that exists in the metadata database. So the CRC patient data will be queryable in i2b2 only if the patient facts in the CRC database are recorded utilizing standard codes that are referenced in the i2b2 metadata (ONT database) (or have been mapped to these standard codes as part of an ETL process).

For instance, if the patient's electronic health record indicates that the patient had the procedure "tonsillectomy with adenoidectomy," then that fact needs to be recorded in the CRC database using the standard code for that particular procedure. In the case of using the default i2b2 Procedures metadata tree, that code would be "ICD9:28.3". When a researcher makes a query in the user interface for "tonsillectomy with adenoidectomy," that query will be translated by i2b2 into a query in the CRC database for patients who have the code ICD9:28.3 in their data records.

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