Information Technology Reference
In-Depth Information
As shown in Figure 23.6, the influence is an increasing function. This may in-
troduce some problems of representation or loss of precision when the values are
very high. The definition of the influence that we have proposed allows us to avoid
this problem in an easy way. We only have to move the reference date (
D
R
)and
adapt the stored values to get an easy and quick adaptation: if we add one year to
the reference date and divide all the values by 2, we get the same frequency and we
reduce the magnitude of the stored values.
We can repeat this process as many time as needed as long as the final reference
date is previous to the next access to be stored. The proposed system will do this
each new year keeping the reference day with one year length to actual date. The
update of the values only need to change the reference date (one update sentence)
and the stored values (a set of very simple update sentences) which would need just
a short time.
Now we have the frequency, we propose an adaptation of the
inverse document
frequency
of the Vector Space Model [49] to measure the pertinence of a data group
to a context, based on the information stored in the RADB database.
Definition 35.
Let C
be a
context and X
a
data
groups,
the
restrospective
pertinence
is
tf
XC
tf
C
]
P
R
(
1
/
4
X
)=[
(23.4)
The idea behind this pertinence is to consider relevant a
data group
if the number of
accesses to it is high in comparison to the total number of accesses.
Global Pertinence
Once we have the different considered aspects about the pertinence and defined a
way to compute them them, we need to aggregate the information given by them
into a single value. To do it, we obtain a global pertinence of a data group to a given
context as in next definition.
Definition 36.
Let
X
be a
group of data
in a document
D
, and
C
a
context
, we define
the
global pertinence of X to C
as
P
G
(
P
Dc
(
P
Dc
(
P
Dc
(
P
R
(
X
)=(
X
)
⊕
X
)
⊕
X
)
⊕
X
))
⊗
P
T
(
D
)
(23.5)
where
P
Dc
is the pertinence set by medical doctors according to the regulations,
•
P
Dc
(
•
is the pertinence set by medical doctors for the data group to the context
under their personal point of view,
X
)
P
Dc
(
•
X
)
is the pertinence set by medical doctors for the data group to a given
patient,
P
R
(
•
X
)
the retrospective pertinence according to prior accesses,
•
P
T
(
X
)
the pertinence considering the age of the document,
•⊕
and
⊗
a t-conorm and a t-norm respectively.
