Databases Reference
In-Depth Information
Comments:
Increasingly, temporal data must be available on-line, just as current data
is. Transactions to maintain temporal data must be as easy to write as are
transactions to maintain current data. Queries to retrieve temporal data,
or a combination of temporal and current data, must be as easy to write
as are queries to retrieve current data only. (From Chapter 1.)
semantic logfile
Semantics:
the set of all past assertions and empty assertions in an asserted
version table.
Comments:
See also:
physical logfile
.
The contents of a physical logfile of a particular table, as of point in time
X, are all those rows physically present in the table as of that point in
time. The contents of a semantic logfile of that table, as of that point in
time, are all those rows asserted on or prior to that point in time. The
difference is the set of all assertions which are deferred assertions as of
that point in time.
Components:
asserted version table, assertion, empty assertion.
shared assertion time
Mechanics:
the shared assertion time of two or more versions are all those
assertion time clock ticks that include both their assertion time periods.
Semantics:
the shared assertion time of two or more versions is the assertion time
period within which they are commensurable.
Components:
assertion time, assertion time period, clock tick, (in)
commensurable, version.
state
Semantics:
the set of values in the business data columns of a row in an asserted
version table which describes the properties and/or relationships which
the object represented by that row has at a point in time or over a period
of time.
Components:
asserted version table, business data, object, point in time,
represent, time period.
statement
Mechanics:
what is said to be the case by a currently asserted row in an asserted
version table.
Semantics:
what is asserted, during a specified period of current assertion time,
is true of a referenced object during a specified period of effective time.
Comments:
In Asserted Versioning, a row in past assertion time is a record of a
statement we once made, and a row in future assertion time is a record of
a statement that we may make at some point in the future. Neither are
statements because neither have truth values.
Components:
asserted version table, assertion, assertion time period, currently
asserted, effective time period, object, referent.
successor
Mechanics:
a row in an asserted version table that supercedes all or part of
another row.
supercede
