Databases Reference
In-Depth Information
tables (not necessarily distinct). At the level of instances, it is a
relationship between two rows of relational tables (which are,
however, necessarily distinct).
An RI relationship between a child row and a parent row is
based on an
existence dependency
between the objects they rep-
resent. In our examples, policies are objects which are existence-
dependent on clients, who are also objects. Reflecting that fact,
and precisely because of it, rows in Policy tables are referentially
dependent on rows in Client tables.
Existence dependency, of course, does not have to be a cause-
and-effect dependency between two physical objects, although
that is one kind of existence dependency. For example, as we just
pointed out, there is an existence dependency of policies on cli-
ents; yet neither policies nor clients are physical objects. A policy
is a contract, an agreement recognized in civil law. A client is a
party to such a contract. The existence dependency of a policy
on a client is thus a dependency of one legal object on another,
a dependency defined in the world of law, not in the world of
physics.
In this chapter, we will see how
temporal referential integrity
(TRI)
is referential integrity applied to the temporalized
representations of objects by two types of managed objects—
episodes and versions. A TRI relationship between a child man-
aged object and a parent managed object is based on an exis-
tence dependency between the objects which those managed
objects represent.
In either an RI or a TRI relationship between a managed
object representing a policy and one representing a client, a cli-
ent may exist without a related policy, but a policy cannot exist
without a related client.
1
These “mays” and “cannots”, as far as
RI is concerned, are enforced on the managed objects which
are rows, by the DBMS, in accordance with rules declared to it
in DDL statements as constraints. These “mays” and “cannots”,
as far as TRI is concerned, are enforced on the managed objects
which are versions and episodes, by the AVF, in accordance with
rules declared to it as entries in metadata tables.
1
Throughout this topic, we have been referring to the individuals who own policies as
“clients”. But in fact, the health insurance industry refers to these individuals as
“members”, i.e. members of insurance plans. We made the terminological change
because the word “member”, used in this way, is unfamiliar outside the health
insurance industry.
