Databases Reference
In-Depth Information
evaluates to
True
. If there is no such episode, then the function
evaluates to
False
, and that version will never be added to the
database because if it were, it would violate TRI.
If the AVF finds such an episode, in carrying out this function, it
does not have to check further to insure that there is only one such
episode. If there weremore than one, then those episodes would be
in TEI conflict across all their clock ticks which [intersect]. The AVF
does not allowTEI violations to occur, so if there is a TRI parent epi-
sode for the TFK reference, there is only one of them.
For example, the
oid
value in the TFK of P861-A(2) picks out
client C903. Before the AVF added that version to the database,
it used the
f
TRI function to determine whether or not it was ref-
erentially valid.
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That TRI validation check would look some-
thing like this:
IF ISTRUE(fTRI(Client, C903, [Jul10 - 9999])) THEN
{add the version}
ELSE
{notify the calling program of a TRI error}
ENDIF
Together, the explicit and implicit parts of the TFK, its data ele-
ment part and its function part, complete an unambiguous refer-
ence from a TFK to the one episode which satisfies the TRI
constraint on the relationship from that version to that episode.
Note that this description of a TFK is a semantic description, not
an implementation-level description. The
f
TRI function is one
component of a TFK. Its representation here is obviously not source
code that could be compiled or interpreted. But however it is
expressed, whether in the AVF or in some other framework based
on these concepts, it is a function; and without it, the columns of
data we call TFKs are not TFKs. Those columns of data are simply
those components of TFKs which can be expressed as data.
Temporal Transactions and Associative
Tables
In a non-temporal database, an associative table, often infor-
mally referred to as an
xref
table, implements a many-to-many
relationship between two other tables. Each of those other tables
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This is a logical description of what the AVF does. It does not imply that the AVF
code makes a single function call to carry out its TRI checks, let alone that it calls a
function named
f
TRI.
