Databases Reference
In-Depth Information
within the distinction between keeping track of changes over
time as a series of events or as a series of states through which
objects pass, we situated Asserted Versioning as a method of
managing data which describes the states through which persis-
tent objects pass as they change over time. At the third level of
the taxonomy, we distinguished between the management of
data along a single temporal dimension from the management
of data along two temporal dimensions, and situated Asserted
Versioning as a method in the latter category. Finally, within
the category of the management of queryable bi-temporal data
about persistent objects, we distinguished Asserted Versioning
from the standard temporal model on the basis of its manage-
ment of future assertion time and its encapsulation of the
mechanisms which enforce temporal semantics.
In Part 2, we introduced the core concepts of Asserted Versioning,
reviewed the schema common to all asserted version tables, and
developed a scenario which illustrates the use of basic temporal
insert, update and delete transactions. The most basic concept of
Asserted Versioning is that of a persistent object. Although hardly a
novel concept, we believe that the organization of methods of tem-
poral data management on the basis of that concept is novel.
Like the standard temporal model, Asserted Versioning
distinguishes two temporal dimensions in which persistent
object data is located. The ontological dimension is called effec-
tive time in Asserted Versioning, and valid time in both the
standard model and in the computer science community. The
epistemological dimension is called assertion time in Asserted
Versioning, and transaction time in the standard model and
by computer scientists; and it is here that their accounts and
ours differ.
Asserted Versioning manages data located in future assertion
time, while the standard model ignores the notion of future
transaction time. Asserted Versioning also emphasizes that effec-
tive time exists within assertion time, while the standard model
seems to treat its two temporal dimensions as orthogonal.
With the completion of Parts 1 and 2, all the preliminary work
is behind us. Part 3 is an in-depth presentation of Asserted
Versioning itself. It begins with Chapter 8, in which we discuss
how temporal design requirements are expressed in metadata
associated with a conventional logical data model, how this
metadata is used to convert non-temporal table schemas into
bi-temporal table schemas, and also how it is used to generate
the code, such as stored procedures, that enforce both temporal
entity integrity and temporal referential integrity on those tables.
If ERwin is used as the data modeling tool, then a set of ERwin
