Databases Reference
In-Depth Information
row the query author is interested in, two of those components
being time periods that may or may not intersect in various
ways. Continuing on, consider the possibilities involved in join-
ing bi-temporal tables to one another, or to uni-temporal tables,
or to non-temporal tables!
This is where computer science gets put to good use. By now,
after more than a quarter-century of research, academics are
likely to have identified most of the complex issues involved in
managing temporal data, even if they haven't come to an agree-
ment on how to deal with all of them. And given the way they
think and write, they are likely to have described these issues,
albeit in their own mathematical dialects, at a level of detail from
which we IT professionals can both design and code with confi-
dence that further bi-temporal complexities probably do not lie
hidden in the bushes.
So one reason IT practitioners should not look at
Figures Part 1.1, Part 1.2 and Part 1.3
and conclude that there
is nothing new here is that there is a great deal more to manag-
ing temporal data than just writing the DDL for temporal
schemas. And if many practitioners remain ignorant of these
complexities, it is probably because they have never made full
use of the entire range of uni-temporal functionality, let alone
of bi-temporal functionality. In fact, in our experience, which
between us amounts to over a half-century of IT consulting,
for dozens of clients, we have seen little in the way of temporal
data management beyond a limited use of the capabilities of
uni-temporal versioned tables.
So for most of us, there is a good deal more to learn about
managing temporal data. Most of the code that many of us have
written to make sure that uni- or bi-temporal updates are done
correctly addresses only the tip of the iceberg of temporal data
management complexities.
To summarize our prospectus of Part 1, Chapter 1 will be a
history of how the business IT world has managed the intersec-
tion of time and data. Chapter 2 will be a taxonomy of those
methods, whose purpose is to highlight the similarities and
differences among them.
Glossary References
Glossary entries whose definitions form strong interdepen-
dencies are grouped together in the following list. The same
Glossary entries may be grouped together in different ways at
the end of different chapters, each grouping reflecting the
