Soft Aggregation in Flexible Databases Querying based on the Vector p-norm

Flexible querying of databases is recognized as a useful feature to aid users in finding what they need. When a traditional SQL query is submitted to a relational database, often two unpleasant scenarios may occur: either an empty answer is obtained as a result of a too selective query, or too many undifferentiated answers (records or tuples) are retrieved. A flexible query allowing the specification of preferences on attributes values of selection conditions (i.e., tolerant or soft selection conditions), and relative appraisal between conditions, intended as preference weights of conditions, is a useful means to produce discriminated answers. In this paper a model of soft aggregation of preferences in flexible database querying is proposed, based on the vector p-norm operator. The model allows to aggregate conditions with distinct importance. We outline how the semantics of the compound query varies for increasing values of the parameter p, when the selection conditions are ANDed and ORed.