Global Positioning System Reference
In-Depth Information
Relevant Link RLintA-A
A RLintA-A link leads to remove irrelevant attributes in the case where the
initial schema has all the attributes associated with an object. Otherwise,
it allows the determination of relevant attributes that are not included in
the initial schema.
A RLintA-A link binds two sets of attributes of a class, possibly
reduced to a singleton. This RL is defi ned by the following elements: the
class concerned by the RL (c
i
), the set of source attributes (A
s
) and the set
of target attributes (A
t
). These two sets, A
s
and A
t
, are disjoint. We say that
the source attributes semantically determine the target attributes. Table 4
presents the formal defi nition of RLintA-A.
This defi nition means that in the initial schema where it exists the set
of (source) attributes {a
s1
,..., a
sn
}, this RL adds in the fi nal schema, the set
of (target) attributes {a
t1
,..., a
tm
}. Note here that all the attributes are not
necessarily involved in this RL (e.g., key attribute). In fact, the key is not
taken into account because keys operate at the functional dependency level
in a database schema design.
As an example, from an agronomic point of view, a user who already
has tree species, the phytosanitary status of the trees represents relevant
information. Therefore, we defi ne a RLintA-A link between two attributes
of the Tree class (e.g., “species” and “phytosanitaryStatus”). This RL is
defi ned by: -A_A> (Tree, species) = phytosanitaryStatus.
Operational complexity depends on the implementation of the database.
The database administrator is in charge of defi ning such a complexity. It may
be constant as defi ned for example in a framework of a relational database
with sets materialization of source and target attributes in the same relation
(the same tuple). It can be higher due to the third normal form, with or
without index(es) in the second (third) relations. The complexity may be
changed out of computed attributes (i.e., the complexity depends on the
complexity of the evaluation).
Table 4.
Formal defi nition of
RLintA
-
A.
Let c
i
= (A
i
, M
i
, K
i
) be a class where c
i
∈ C. Let A
s
= {a
s1
,..., a
sn
} be a set
of attributes. Let A
t
= {a
t1
,..., a
tm
} be a set of attributes
Pre-conditions
: A
s
⊆ A
i
, A
t
⊆ A
i,
A
s
∩ A
t
= ∅, K
i
⊄ A
s
, K
i
⊄ A
t
A RL of
RLintA-A (-A_A->)
type between A
s
and A
t
is defined by:
-A_A-> : C x A x .. x A -> A x .. x A
-A_A-> (c
i
, a
s1
,..., a
sn
) = (a
t1
,..., a
tm
)
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