Data Summarization in Relational Databases through Fuzzy Dependencies

In this paper we deal with the problem of treating with dependencies in relational databases which do not hold in an exact manner as classical functional dependencies but in a weaker sense, i.e., we face with relations which satisfy dependencies such that `people with similar age and height have similar weight'. We model this relationship through the concept of fuzzy dependency. We see that these dependencies imply some kind of fuzzy redundancy, and, in order to avoid it, we propose to use a projection operator which leads us to partition a relation r into two projections, say r1 and r2 with a less amount of information. Then, we proceed to replace the original relation by these projections. In this process we must guarantee that we can recover the data we had in the original relation. This will be possible by using a special join operator applied to r1 and r2. We must also guarantee that we can test the fuzzy dependency for new entries to the database in the same way either if we consider the original relation r or if we work with the projections r1 and r2. We also show that this de®nition of dependency maintains the good properties of completeness of the classical case. Ó 1999 Elsevier Science Inc. All rights reserved.