Databases Reference
In-Depth Information
snapshots and versions is conceptually confused and
confusing. Asserted Versioning makes real-time data
warehousing neither necessary nor desirable.
(v) Temporalized Unique Indexes. A development topic. Values
which are unique to one row in a conventional table may
appear on any number of rows when the table is converted
to an asserted version table. So unique indexes on conven-
tional tables are no longer unique after the conversion. To
make those indexes unique, both an assertion and an
effective time period must be added to them. This reflects
the fact that although those values are no longer unique
across all rows in the converted table, they remain unique
across all rows in the table at any one point in time, specif-
ically at any one combination of assertion and effective
time clock ticks.
(vi) Instead Of Triggers. A development topic. Instead Of
triggers function as updatable views. These updatable
views make Asserted Versioning's temporal transactions
look like conventional SQL. When invoked, the triggered
code recognizes insert, update and delete statements as
temporal transactions. As described in this topic, it will
translate them into multiple physical transactions, apply
TEI and TRI checks, and manage the processing of those
physical transactions as atomic and isolated units of work.
The utilization of Instead Of triggers by the AVF is ongoing
work, as we go to press.
(vii) Java and Hibernate. A research and development topic.
Hibernate is an object/relational persistence and query
service framework for Java. It hides the complexities of
SQL, and functions as a data access layer supporting
object-oriented semantics (not to be confused with the
semantics of objects, as Asserted Versioning uses that
term). Hibernate and other frameworks can be used to
invoke the AVF logic to enforce TEI and TRI while
maintaining an Asserted Versioning bi-temporal database.
(viii) Archiving. A methodology topic. An important archiving
issue is how to archive integral semantic units, i.e. how
to archive without leaving “dangling references” to
archived data in the source database. Assertions, versions,
episodes and objects define integral semantic units, and
we are developing an archiving strategy, and AVF support
for it, based on those Asserted Versioning concepts.
(ix) Star Schema Temporal Data. A methodology topic. Bi-
temporal dimensions can make the “cube explosion prob-
lem” unmanageable, and bi-temporal semantics do not
