Databases Reference
In-Depth Information
(In any formalization of this Glossary, of course, this homonym would
have to be resolved. In this topic, we rely on context to do so.)
Components:
event.
transaction begin date
Mechanics:
in the standard temporal model, the date a row is physically inserted
into a table.
Semantics:
in the standard temporal model, the date which designates the start of
the transaction time period of a row, using the closed-open convention.
Comments:
Another one of the several homonyms of “transaction”.
Components:
closed-open, temporal data management taxonomy {the standard
temporal model}, transaction time period.
transaction table
Semantics:
a table whose rows represent events.
Comments:
Transaction tables record the
events
that change the states of objects and,
in particular, the relationships among them. (From Chapter 1.)
Transaction tables are often used as the fact tables in fact-dimension data
marts.
There can be only one version of an event, since events do not persist and
change over time. Multiple rows for the same event can only be multiple
assertions about that event, presumably a series of corrections to the
data.
Components:
events.
transaction time
Description:
“A database fact is stored in a database at some point in time, and
after it is stored, it may be retrieved. The transaction time of a database fact is
the time when the fact is stored in the database. Transaction times are
consistent with the serialization order of the transactions. Transaction time
values cannot be after the current time. Also, as it is impossible to change the
past, transaction times cannot be changed. Transaction times may be
implemented using transaction commit times.” From [Jensen, 1992].
Comments:
As defined by Jensen, the computer science term “transaction time” may
be treated as co-extensive with our term “row creation date”. But the two
terms cannot be said to be
synonymous
because they are defined by
means of two vocabularies between which semantic correlations have not
been established. Also, while Jensen's definition, given here, indicates that
transaction time is a point in time, Snodgrass's use of the term, in
[Snodgrass, 2000] has it referring to a period of time, usually open-ended,
but not necessarily so. In this second sense, the term is co-extensive with
a proper subset of our term “assertion time period”.
transaction time period
Mechanics:
the assertion and effective time periods specified on a temporal
transaction.
Semantics:
the set of assertion time and effective time clock ticks outside of
which a temporal transaction will have no effect on the database.
Comments:
In this entry, “transaction” refers to “temporal transaction”, not to any of
the other homonyms of “transaction”.
