The form in which records are represented may have a substantial impact on the efficiency,
accuracy and completeness of retrieval. The forms that best suit retrieval may differ
from the forms that are required to meet the principles of clinically safe and legally
valid
.
This option leaves information in the form entered in the
with no additions to assist future retrieval. The application must do all the work
needed to locate the required records and compute subsumption and
when a request is made to retrieve data.
An innovative approach to the issues raised by literal storage of
is to implement an
repository. Each unique
used in the system is stored in a referenced database table and assigned an internal
unique
(e.g. a
). When an
is used in a clinical record entry the unique
id is used to reference the
in the repository.
The key advantages of this approach of this approach are:
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One possible approach to optimization of retrieval is to
the original stored information into an equivalent representation with the minimum
number of
components.
The objective of this approach is to allow the generation of simple indices for the
representation. It is then possible to undertake most retrievals using the
to compute whether
in the record are
of the
used to specify retrieval. Where
is required, the minimum number of additional tests are required to confirm that
a
in the record meets the specified retrieval criteria.
One difficulty with this approach is that there may be more than one representation
that requires the same degree of
. This is discussed in more detail and illustrated in
Transforming expressions to normal forms .
If this approach is adopted additional rules need to be applied to determine the choice
between alternatives with a similar number of
components.
Example:
In the hypothetical example illustrated in , the
"red steel pedal bicycle", for which no
representation exists, could be represented as:
"red pedal bicycle" +
=
or
"steel pedal bicycle" + " color " = "red"
Both are equally close to the objective of minimizing
. A rule is needed to determine which of these is preferred. There is no obvious right
or wrong solution to this but a simple rule that places the attributes in an
will, if applied consistently, allow all
representations to be reduced to a single minimized form.
An alternative approach is to expand any
in the record to their fullest possible
forms. This general type of
is illustrated in
Transforming expressions to normal forms .
This approach requires a richer record structure but has the advantage that there
are three possible end-points to
, each of which ensures that any computably equivalent representations of
will expand to an identical
form. The three end-points are summarized here:
If the retrieval criteria are expressed in a similar form, a relatively simple
can interrogate the record for all entries with a matching set of
and specified characteristics.