Commonly, two main classes of formal testing techniques are applied to check the conformance of protocols and software: active and passive testing (monitoring) techniques. Because of many industrial constraints such as the necessity to achieve implementation black box testing, passive testing techniques become highly relevant in several cases. Besides, most of the passive testing techniques only consider control portions of exchanged packets and ignores data parts. However, since systems become more complex, testing for data constraints and relations between packets is now essential. In this paper we propose a novel approach for defining data oriented invariants and show how they can be tested in a trace set by using logic programming. Experimental results on SIP protocol traces are provided