Does Chronus support temporal projections?
Yes. Many temporal queries will wish to project selected columns in a table before operating on them. The resulting projection may be coalesced or uncoalesced. Given that many temporal queries will operate in this way, we would like to avoid requiring that the projection be performed in a separate SELECT statement because this approach would necessitate the writing of two SELECT statements for many temporal queries. Instead, we allow projection to be performed in the FROM clause of a SELECT statement. These projections are named so that we can refer to them in the subsequent WHERE clause. They are coalesced by default; the keyword UNCOALESCED may be used to turn off coalescing. Suppose we had the following table called EMPLOYEE and wanted to select people who had worked for more than two months at any job. Name Job ValidTime J. Smith doctor {[14/Feb/2002-‘+’]} P. Jones dentist {[1/Apr/2002-‘+’]} R.
