150
Omar Boucelma, Mehdi Essid, and Yassine Lassoued
For example, if κ vr denotes the quality assertion that describes the element
vCommL of data source TQe that corresponds to class Road of the global schema,
then we have
κ vr (Q
1
0 , Road) = [−72, −71.5] × [45.375, 45.5],
κ vr (Q
2
1 , Road) = {‘Ministry of Natural Resources of Quebec’},
· · · ,
κ vr (Q
2
6 , Road) = [0, 1%].
The advantage of such representation is that it allows the expression of implicit
preference relationships without having to define them. For example, to express that
the deficit rate of a class E is better than 1% according to a quality assertion κ, we
use the expression:
κ(C
1
1 , E) = [0, 1%].
Quality Comparison
In order to answer users’ queries, we need to know if the quality of some dataset
satisfies a given (quality) condition. As we use quality assertions to represent quality
information as well as quality conditions, we need to make these assertions comparable.
Consider two quality assertions κ and γ. If the parameter Q 0 is applicable to a
given element E, then we say that κ satisfies γ for the element E according to the
sub-parameter Q 0 if the following condition is satisfied:
κ(Q 0 , E) ∩ γ(Q 0 , E) ∅.
In other words, the spatial cover specified by assertion κ satisfies that of γ if both of
them overlap.
An example of quality comparison is illustrated in Fig. 7.13. Each parallelepiped
in this figure represents the quality value for a given assertion, but related to the same
element. Only the spatial cover and the accordance rate are represented here and they
form a three-dimensional space. A satisfying quality value for that represented by P
corresponds to the parallelepiped P
. On the contrary, P
and P
do not satisfy P.
Source Description
A source description specifies the mappings between the global schema and the
source schema. Source descriptions are used by the mediator during query rewriting.
In order to ensure expressive and generic correspondences between schemas, we use
mapping functions (such as restrictions, concatenation, conversion functions, geometrical, or topological functions, specific administrator-defined functions, etc.). In
the definition of a mapping below, we introduce a quality assertion, while in Sect. 7.4,
we used constraints.
Omar Boucelma, Mehdi Essid, and Yassine Lassoued
For example, if κ vr denotes the quality assertion that describes the element
vCommL of data source TQe that corresponds to class Road of the global schema,
then we have
κ vr (Q
1
0 , Road) = [−72, −71.5] × [45.375, 45.5],
κ vr (Q
2
1 , Road) = {‘Ministry of Natural Resources of Quebec’},
· · · ,
κ vr (Q
2
6 , Road) = [0, 1%].
The advantage of such representation is that it allows the expression of implicit
preference relationships without having to define them. For example, to express that
the deficit rate of a class E is better than 1% according to a quality assertion κ, we
use the expression:
κ(C
1
1 , E) = [0, 1%].
Quality Comparison
In order to answer users’ queries, we need to know if the quality of some dataset
satisfies a given (quality) condition. As we use quality assertions to represent quality
information as well as quality conditions, we need to make these assertions comparable.
Consider two quality assertions κ and γ. If the parameter Q 0 is applicable to a
given element E, then we say that κ satisfies γ for the element E according to the
sub-parameter Q 0 if the following condition is satisfied:
κ(Q 0 , E) ∩ γ(Q 0 , E) ∅.
In other words, the spatial cover specified by assertion κ satisfies that of γ if both of
them overlap.
An example of quality comparison is illustrated in Fig. 7.13. Each parallelepiped
in this figure represents the quality value for a given assertion, but related to the same
element. Only the spatial cover and the accordance rate are represented here and they
form a three-dimensional space. A satisfying quality value for that represented by P
corresponds to the parallelepiped P
. On the contrary, P
and P
do not satisfy P.
Source Description
A source description specifies the mappings between the global schema and the
source schema. Source descriptions are used by the mediator during query rewriting.
In order to ensure expressive and generic correspondences between schemas, we use
mapping functions (such as restrictions, concatenation, conversion functions, geometrical, or topological functions, specific administrator-defined functions, etc.). In
the definition of a mapping below, we introduce a quality assertion, while in Sect. 7.4,
we used constraints.