Data summarization in relational databases through fuzzy dependencies

In this paper we deal with the problem of treating with dependencies in rel ational databases which do not hold in an exact manner as classical functio nal dependencies but in a weaker sense, i.e., we face with relations which satisfy dependencies such that 'people with similar age and height have sim ilar weight'. We model this relationship through the concept of fuzzy depen dency. 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 le ads us to partition a relation r into two projections, say r(1) and r(2) wi th a less amount of information. Then, we proceed to replace the original r elation 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 r(1) and r(2). We must also guara ntee 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 r(1) and r(2). We also show that this definition of d ependency maintains the good properties of completeness of the classical ca se. (C) 1999 Elsevier Science Inc. All rights reserved.