Efficient processing of distributed set queries

The problem of efficiently processing queries that manipulate sets is considered with the objective of minimizing the processing cost by reducing the size of transmitted data as much as possible. The semantics of set operations is used to achieve this goal. A set query has the general form SET 1 op SET 2. For two sets to be related by a set operation, their sizes should satisfy a necessary condition. For the two sets to be equal, they should have the same size. For SET 1 to be a subset of SET 2, its size should be less than or equal to the size of SET 2. In the relational model, given two attributes, the size of a set of values from one attribute that is associated with a value from the other attribute can be determined using functional dependency between the two attributes. Using these semantics, a distributed set query can be converted into a distributed nonset query. When the two sets are of size greater than one, however, the query cannot be converted into a nonset query. It is converted into another distributed set query. The size of data transmitted to answer the new query is reduced as much as possible. This is done by sending sets that satisfy the necessary condition of the set operation