Databases Reference
In-Depth Information
find it useful to emphasize the distinction between objects and
managed objects. But if we do occasionally speak of software doing
something to an object, that will simply be a non-tendentious
shorthand for speaking about software doing something to a man-
aged object which represents that object.
This basic sequence of insert, update and delete transactions
accounts for most of the activity against any table, whether non-tem-
poral or bi-temporal. And just as we usually don't know if or when
updates to a non-temporal row will occur, and if or when it will be
deleted, so too, as each row representing some stage in the life his-
tory of an object is inserted into a bi-temporal table, we usually don't
know if or when another row for that same object will come along.
In this chapter, we will follow a sequence of basic temporal
transactions. Temporal transactions are inserts, updates and
deletes whose target is an asserted version table. As we explained
in Chapter 5, all asserted version tables are bi-temporal tables.
Uni-temporal assertion tables and uni-temporal version tables,
as we sometimes call them, are actually
views
on bi-temporal
tables. Conventional tables, which we also call non-temporal
tables, are the third kind of view which can be defined on
Asserted Versioning's physical bi-temporal tables.
Basic temporal transactions
are temporal transactions that do
not specify any bi-temporal parameters. As we will see later, any
one or more of three bi-temporal parameters—an assertion
begin date, an effective begin date or an effective end date—
may be specified on a temporal transaction. On a
basic
temporal
transaction, none of them are specified.
By starting out with basic temporal transactions, we can
introduce the most common sequence of transactions that occur
against asserted version tables, and show how these transactions
are processed. In chapters that follow, we will examine temporal
transactions which are not basic, and whose processing is con-
siderably more complex, although because of the maintenance
encapsulation provided by Asserted Versioning, are just as easy
for the user to write as are basic temporal transactions.
The Representation of Objects in Time
Periods
The basic scenario, and by far the most commonly encoun-
tered one, is for a series of updates that would overwrite data
in a conventional table to result in an effective-time contiguous
series of versions in an asserted version table. Just as it is logi-
cally impossible to apply an update to a conventional table that
