This constraint says that for any two tuples u1 and u2 such that u1[FINGERPRINT] is considered similar within the threshold t1 to u2[FINGERPRINT] by the FINGERCODE, then u1[PHOTO] is considered similar within the threshold t2 to u2[PHOTO] by the QBIC. Given the semantics of the FINGERPRINT attribute it is reasonable that a designer would chose a value of t1 close to zero.