Estimating list sizes in partial joins (Q1842428)

The paper is an extension of the investigation of a mapping of a relational data model to a list model, especially a partial join is considered. In this mapping for a realisation of the relation \(R\) there exists a list realisation --- a list \(s\). Between the join operator and the projection operator on the list \(s\) is the relationship: the result of the natural join operation can be obtained by taking the projection on the list \(s\). To build up the above mentioned mapping the size of the list \(s\) is important. In the paper a simple expression for a static estimate of the list size has been found. A discussion about the advantage/disadvantage of list representation of data and join indices is added. The paper is a contribution to the long execution time problem of the natural join operation.