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000034_rts _Fri Mar 12 13:14:00 1993.msg
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Received: from boojum.cs.arizona.edu by optima.cs.arizona.edu (5.65c/15) via SMTP
id AA17404; Fri, 12 Mar 1993 13:14:01 MST
Date: Fri, 12 Mar 1993 13:14:00 MST
From: "Rick Snodgrass" <rts>
Message-Id: <199303122014.AA29082@boojum.cs.arizona.edu>
Received: by boojum.cs.arizona.edu; Fri, 12 Mar 1993 13:14:00 MST
To: tsql@cs.arizona.edu
Subject: more definitions
Lots of work is now going on in a subdiscipline of temporal databases,
that of spatiotemporal databases. The March, 1993 issue of SIGMOD
Record lists all the papers through December, 1992 in this area.
In the following, I extend five of the previous terms in the glossary
to also apply to spatiotemporal databases.
Comments and critique would be welcome.
Sincerely,
Rick
\subsection{Spatiotemporal as Modifier}
\entry{Definition}
The modifier {\em spatiotemporal} is used to indicate that the
modified concept concerns simultaneous support of some aspect of time
and some aspect of space, in one or more dimensions.
\entry{Alternative Names}
Spatio-temporal, temporal-spatial, space-time-oriented.
\entry{Discussion}
This term is already in use, interchangeably with ``spatio-temporal,''
in the geographic information systems community (+E3) (hence, the
preference over ``temporal-spatial''), and is consistent with the
``temporal'' modifier (+E7). Avoiding the hyphen makes it easier to
type (+E2), another reason to prefer it over ``temporal-spatial''. It
may be applied generically as a modifier for ``database,''
``algebra,'' ``query language,'' ``data model,'' and ``DBMS.'
\subsection{Spatial Quantum}
\entry{Definition}
A {\em spatial quantum} (or simply {\em quantum}, when the sense is
clear) is the shortest distance (or area or volume) of space supported
by a spatial DBMS---it is a nondecomposable region of space. It can be
associated with one or more dimensions. A particular
unidimensional quantum is an interval of fixed length along a single
spatial dimension. A particular three-dimensional quantum is a fixed-sized,
located cubic volume of space.
\entry{Alternative Name}
Spatial unit.
\entry{Discussion}
We prefer ``spatial quantum'' to ``spatial unit'' because spatial distances
and volumes are usually given as measurements of some unit (such as meters),
but the ``unit of measurement'' is not the same as
the ``spatial quantum.'' The former term (``spatial quantum'')
is more precise (+E9), in part,
because it avoids this possible confusion.
\subsection{Spatiotemporal Quantum}
\entry{Definition}
A {\em spatiotemporal quantum} (or simply {\em quantum}, when the
sense is clear) is a non-decomposable region in two, three, or
four-space, where one or more of the dimensions are spatial and the
rest, at least one, are temporal.
\entry{Alternative Name}
Spatiotemporal unit, spatiotemporal chronon.
\entry{Discussion}
This term is a generalization of chronon and spatial quantum.
``Unit'' is perhaps less precise (-E9). `Chronon' specifically relates
to time, and thus is inconsistent with the adjective `spatiotemporal'.
\subsection{Spatiotemporal Interval}
A {\em spatiotemporal interval} is a region in $n$-space, where at
least one of the axes is a spatial dimension and the remaining axes
are temporal dimensions, with the region having sides that are
parallel to all axes. It identifies when and where a fact was true.
\entry{Alternative Names}
None.
\entry{Discussion}
A spatiotemporal interval can be represented by a non-empty set of
spatiotemporal quanta.
\subsection{Spatiotemporal Element}
\entry{Definition}
A {\em spatiotemporal element} is a finite set of
spatiotemporal intervals. Spatiotemporal elements are closed under the
set theoretic operations of union, intersection and complementation.
\entry{Discussion}
This is the natural generalization of ``temporal element.''
It can be represented with a set of spatiotemporal quanta.