XML blobs are utilized by filling the column C_METADATAXML in the table I2B2 with a certain XML data structure which is saved in the database as a single Character Large Object.They are made for representing laboratory values and similiar observations that uses qualifying statements like "abnormal" or "primary".

XML blobs are also recommended for numeric values if the user knows the specific value beforehand (EHR ID or a given age).

Theoretically, XML blobs could also be used for representing simple code lists, but there is hardly any advantage compared to i2b2 concept leafs.