Databases Reference
In-Depth Information
The Standard Temporal Model
What we call
the standard temporal model
was developed
by Dr. Rick Snodgrass in his topic
Developing Time-Oriented
Database Applications in SQL
(Morgan-Kaufmann, 2000).
Based on the computer science work current at that time,
and especially on the work Dr. Snodgrass and others had done
on the TSQL (temporal SQL) proposal to the SQL standards
committees, it shows how to implement both uni-temporal
and bi-temporal data management using then-current DBMSs
and then-current SQL.
We emphasize that, as we are writing, Dr. Snodgrass's book is
a decade old. We use it as our baseline view of computer science
work on bi-temporal data because most of the computer science
literature exists in the form of articles in scientific journals that
are not readily accessible to many IT professionals. We also
emphasize that Dr. Snodgrass did not write that topic as a com-
pendium of computer science research for an IT audience.
Instead, he wrote it as a description of how some of that research
could be adapted to provide a means of managing bi-temporal
data with the SQL and the DBMSs available at that time.
One of the greatest strengths of the standard model is that it
discusses and illustrates both the maintenance and the querying
of temporal data at the level of SQL statements. For example, it
shows us the kind of code that is needed to apply the temporal
analogues of entity integrity and referential integrity to temporal
data. And for any readers who might think that temporal data
management is just a small step beyond the versioning they
are already familiar with, many of the constraint-checking
SQL statements shown in Dr. Snodgrass's book should suffice
to disabuse them of that notion.
The Asserted Versioning Temporal Model
What we call
the Asserted Versioning temporal model
is our
own approach to managing temporal data. Like the standard
model, it attempts to manage temporal data with current tech-
nology and current SQL.
The Asserted Versioning model of uni-temporal and bi-tem-
poral data management supports all of the functionality of the
standard model. In addition, it extends the standard model's
notion of transaction time by permitting data to be physically
added to a table
prior
to the time when that data will appear
in the table as production data, available for use. This is done
by means of
deferred transactions
, which result in
deferred
assertions
, those being the inserted, updated or logically deleted
