A Stratum Based Approach to Access Degenerate Temporal Relations

	Mario A. Nascimento, mario@cnptia.embrapa.br

ABSTRACT

We present an approach which yields efficient access to degenerate temporal
relations, i.e., temporal relations where valid time behaves as transaction
time. The approach is built on a stratum between the application and the DBMS
and transforms a temporal relation into two temporal relations.  Access to the
data is accomplished through two standard B+-trees (other indices are
optional). Such B+-trees have trivially specialized node split policies,
yielding a high node utilization ratio. In some existing DBMSs, e.g.,
Oracle’s, such specialization is obtained at the expense of setting a single
parameters when creating the indices. We compare the proposed approach, which
we name 2S, to the  Monotonic B+-tree (Elmasri et al, 1992). For intersection
queries, in all but one of the several investigated scenarios, 2S provided at
least comparable query processing time. On the other hand,  it was always
faster when processing inclusion queries. Our simulations also showed that the
2S approach always yielded a much smaller structure.  The main contribution we
present though, lies in the fact that the 2S approach does not require novel
access structures but well-known B+-trees, available in virtually every DBMS
on the market.  We also present examples of how SQL queries can be written to
explore the proposed approach.