Subject: Proposed glossary terms

From: "Christian S. Jensen" <[email-masked]>
Date: Mon, 30 Nov 1992 10:54:09 +0100

Attached is a handful of proposed terms for the temporal database
glossary.

Best regards,
Christian S. Jensen

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\begin{document}

\subsection{Temporal Specialization}

\entry{Definition}

{\em Temporal specialization} denotes the restriction of the
interrelationship between otherwise independent timestamps in temporal
relations. An example is a bitemporal relation where facts are always
inserted after they were valid in reality. In such a relation, the
transaction time would always be after the transaction time. Temporal
specialization may be applied to relation schemas, relation instances,
and individual tuples.

\entry{Alternative Names}   

Temporal restriction.

\entry{Discussion}

Data models exist where relations are required to be specialized, and
temporal specializations often constitute important semantics about
temporal relations that may be utilized for, e.g., query optimization
and processing purposes.

The chosen name is more widely used than the alternative name (+E3).
The chosen name is new (+E5) and indicates that specialization is done
with respect to the temporal aspects of facts (+E8). Temporal
specialization seems to be open-ended (+E4). Thus, an opposite
concept, temporal generalization, has been defined. ``Temporal
restriction'' has no obvious opposite name ($-$E4).

\subsection{Specialized Bitemporal Relationship}

\entry{Definition}

A bitemporal relation schema exhibits a {\em specialized bitemporal
relationship} if all instances obey some given specialized
relationship between the valid and transaction times of the stored
facts. Individual instances and tuples may also exhibit specialized
bitemporal relationships. As bitemporal tuples obtain
transaction-timestamp values during update, updates may also be
characterized by specialized bitemporal relationships.

\entry{Alternative Names}

Restricted bitemporal relationship.

\entry{Discussion}

The primary reason for the choice of name is consistency with the
naming of temporal specialization (+E1). For additional discussions,
see temporal specialization.

\subsection{Retroactive Bitemporal Relation}

\entry{Definition}

A bitemporal relation schema is {\em retroactive} if each stored fact
of any instance is always valid in the past. The concept may be
applied to bitemporal relation instances, individual tuples, and to
updates.

\entry{Alternative Names}

None.

\entry{Discussion}

The name is motivated by the observation that a retroactive bitemporal
relation contains only information concerning the past (+E8).

\subsection{Predictive Bitemporal Relation}

\entry{Definition}

A bitemporal relation schema is {\em predictive} if each fact of any
relation instance is valid in the future when it is being stored in
the relation. The concept may be applied to bitemporal relation
instances, individual tuples, and to updates.

\entry{Alternative Names}   

Proactive bitemporal relation.

\entry{Discussion}

The choice of ``predictive'' over ``proactive'' is due to the more
frequent every-day use of ``predictive,'' making it a more intuitive
name (+E8). In fact, ``proactive'' is absent from many dictionaries.
Tuples inserted into a predictive bitemporal relation instance are, in
effect, predictions about the future of the modeled reality.  Still,
``proactive'' is orthogonal to ``retroactive'' ($-$E1).

\subsection{Degenerate Bitemporal Relation}

\entry{Definition}

A bitemporal relation schema is {\em degenerate} if updates to it's
relation instances are made immediately when something changes in
reality, with the result that the values of the valid and transaction
times are identical. The concept may be applied to bitemporal relation
instances, individual tuples, and to updates.

\entry{Alternative Names}

None.

\entry{Discussion}

``Degenerate bitemporal relation'' names a previously unnamed concept
that is frequently used. A degenerate bitemporal relation resembles a
transaction-time relation in that only one timestamp is necessary.
Unlike a transaction-time relation, however, it is possible to pose
both valid-time and transaction-time queries on a degenerate
bitemporal relation.

The use of ``degenerate'' is intended to reflect that the two time
dimensions may be represented as one, with the resulting limited
capabilities.

\end{document}