Databases Reference
In-Depth Information
Semantics:
a table whose rows describe the current state of the objects they
represent.
Comments:
In the early part of the topic, used as synonymous with “non-temporal
database”. But starting in Chapter 15, a distinction is drawn in which a
conventional database may contain temporal data about persistent
objects, but not in the form of bi-temporal tables.
Components:
object, represent, state.
conventional table
Mechanics:
a table whose rows have no assertion or effective time periods.
Semantics:
a table whose rows contain data describing what we currently claim
things are currently like.
Components:
assertion time period, effective time period, thing.
conventional transaction
Mechanics:
an insert, update or delete against a conventional table.
Semantics:
a request to create, modify or remove a row in a conventional table.
Comments:
Conventional transactions are SQL insert, update or delete statements.
Components:
conventional table.
current assertion
See also:
currently asserted
.
current episode
Mechanics:
an episode whose episode begin date is earlier than Now() and whose
episode end date is later than Now().
Semantics:
an episode for an object which includes a current version of that
object.
Comments:
An object may have at most one current episode.
A past episode is not a current episode because its effective time period is
past.
A no longer asserted episode is not a current episode because its
assertion time period is past.
An episode all of whose assertions are deferred is not a current episode
because it is not yet asserted.
An episode all of whose versions have an effective begin date in the future
is not a current episode because it has no current version.
Components:
episode begin date, episode end date, Now(), object, version.
current transaction
Mechanics:
a temporal transaction which becomes currently effective as soon as
it is applied to the database, and which also becomes currently asserted as
soon as it is applied to the database.
Semantics:
a temporal transaction which accepts the date the transaction is
submitted as the begin date of the assertion period within which its
transformations will be contained, and also as the begin date of the effective
period within which its transformations will be contained.
Comments:
See also:
deferred transaction, proactive transaction, retroactive
transaction
.
