Databases Reference
In-Depth Information
Note that, in the special sense used here, historical data is data about
persistent objects. Thus, fact/dimension data marts do not provide
historical data because their history is a history of events, not of
objects, and also because they do not make assertion time distinctions.
Components:
asserted version table, effective end date, Now(), persistent object,
state.
implicitly temporal data
Mechanics:
a row in a non-temporal table whose assertion time and/or effective
time is co-extensive with its physical presence in its table.
Semantics:
a row of data whose assertion time and/or effective time is not
expressed by means of one or more columns of data.
Comments:
Thus, rows in conventional tables are implicitly temporal data. No
columns of those tables indicate assertion or effective time periods. Each
row is asserted for as long as it is present in its table, and is in effect for as
long as it is present in its table.
Components:
assertion time, effective time, non-temporal table.
incommensurable
Mechanics:
two asserted version rows are incommensurable if and only if their
assertion time periods do not [
intersect
].
Semantics:
unable to be meaningfully compared.
Comments:
Rows which share no clock ticks in assertion time are semantically and
truth-functionally isolated from one another. They are what philosophers
call
incommensurable
. (From Chapter 6.)
Incommensurability restricts TEI and TRI relationships to managed
objects in shared assertion time.
Components:
Allen relationship [
intersect
], asserted version table, assertion time
period.
inflow pipeline dataset
Mechanics:
a dataset whose destination is one or more production tables.
Comments:
Inflow pipeline datasets are tabular data which will become part of the
production database. They originate with transactions acquired or
generated by a company's OLTP systems. They are either immediately
and directly applied to the production database, or are augmented,
corrected or otherwise transformed as they are moved along an “inflow
data pipeline” leading into the production database.
Components:
dataset, production table.
instance
Semantics:
a thing of a particular type.
Comments:
See also:
type
.
The concepts of types and instances has long history. A related distinction
is that between universals and particulars.
Components:
thing, type.
internalized pipeline dataset, Current Data
Mechanics:
all those rows in asserted version tables which lie in the assertion time
present and also in the effective time present. (From Chapter 13.)
