The aim of this paper is to illustrate how a Plausibility Description Logic, called DLP, can be exploited for reasoning about information sources characterized by heterogeneous data representation formats. The paper first introduces DLP syntax and semantics. Then, a DLP-based approach is illustrated for inferring complex knowledge patterns from information sources being heterogeneous in their formats and structure degrees. Finally, it is described how inferred knowledge might be taken advantage of for constructing user profiles to be exploited in various application scenarios. Among these, that of improving the quality of Web search tools is described in detail.