Databases Reference
In-Depth Information
Asserted Versioning Temporal Extent State Transformations
Create
Modify
Erase
Merge
Split
Lengthen
Shorten
Lengthen
Backwards
Lengthen
Forwards
Shorten
Backwards
Shorten
Forwards
Temporal Insert Transaction
Temporal Delete Transaction
Figure 9.5 A Taxonomy of Temporal Extent State Transformations.
brackets, for example as with [meets], [during
1
], [
intersects
],
etc. We also underline the names of nodes which are not leaf
nodes. We will use a similar convention for this taxonomy of
temporal extent transformations, referring to each of its nodes
by surrounding the name of the node with curly braces, for
example as with {remove}, {shorten forwards},
{shorten
}, etc.
With any type of thing we are concerned with, there are three
basic things we can do with its instances. We can create an
instance of it, modify an existing instance, or remove an
instance. This is reflected in the three nodes of the first level
underneath the root node.
Of course, in the case of episodes, the {erase} transformation
is neither a physical nor a logical deletion. Instead, it is the
action in which the entire episode is
withdrawn
from current
assertion time into past assertion time.
{Create}, {modify} and {erase} are clearly jointly exhaustive of
the set of all temporal extent transformations, and also mutually
exclusive of one another. Thus, at its first two levels, this taxon-
omy is, as all taxonomies must be, a partitioning.
At the level of abstraction we are dealing with, there is no fur-
ther breakdown of either the {create} or {erase} transformations.
Of course, there are variations on those themes, as we will see in
the next chapter. For example, we can create an episode
retroactively, or in current time, or proactively, and similarly for
modifying or erasing an episode.
As for the
{modify
} transformation, we achieve a partitioning
by distinguishing transformations which change one episode
