Database Reference
In-Depth Information
and for the Goguen implication:
(
)
1
if
g
p t
,
w
(
) =
*
g
p t
,
i
i
(10)
(
)
i
g
p t w
,
otherwise
i
i
In the case of dynamic weights, Dubois & Prade (1997) deal with a variable importance w i [0,1]
depending on the matching degree of the associated elementary condition. Basically, while using dynamic
weights and dynamic weight assignments, neither the weights nor the associations between weights
and criteria are known in advance. Both the weights and their assignments then depend on the attribute
values of the record(s) on which the query criteria act as, for example, if the condition “ high salary ” is
not important, unless the salary value is extremely high.
Other Flexible Aggregation Schemes
The use of other flexible aggregation schemes is also a subject of intensive research in flexible, fuzzy
logic based querying. In (Kacprzyk & Ziółkowski, 1986) and (Kacprzyk, Zadrożny & Ziółkowski, 1989)
the aggregation of partial queries (conditions) driven by a linguistic quantifier has been firstly described
by considering conditions:
{
}
p
=
Q out of p ,
, p k
(11)
1
where Q is a linguistic (fuzzy) quantifier and p i are elementary conditions to be aggregated. For example,
in the context of a US based company, one may classify an order as troublesome if it meets most of
the following conditions: “comes from outside of USA”, “its total value is low ”, “its shipping costs are
high ”, “employee responsible for it is known to be not completely reliable”, “the amount of order goods
on stock is not much greater than the amount ordered”, etc.
The overall matching degree may be computed using any of the approaches used to model the linguistic
quantifier driven aggregation. In (Kacprzyk & Ziółkowski, 1986; Kacprzyk, Zadrożny & Ziółkowski,
1989) first the linguistic quantifiers in the sense of Zadeh (Zadeh, 1983) and later the OWA operators
(Yager, 1994) are used (cf. Kacprzyk & Zadrożny, 1997; Zadrożny & Kacprzyk, 2009b).
In Zadeh's approach (1983), a linguistically quantified proposition, exemplified by
Most conditions are satisfied ”,
(12)
is written as:
Qy's are F
(13)
where Q is a linguistic quantifier (e.g., most), Y ={ y } is a set of objects (e.g., conditions), and F is a
property (e.g., satisfied). Importance B may be added yielding:
QBy's are F
(14)
Search WWH ::




Custom Search