Database Reference
In-Depth Information
1. Adding an extra argument to a binary relationship. For example, Ash Fleet
Farm is worth 2 million Merean Schrapnels with a high probability. This
can be modeled by turning the relationship “worth with probability” into
an individual of an anonymous class, WorthRelation1. The WorthRelation1
individual then has its own properties,
worth_amount
and
with_probability .
Both these properties are defined as functional properties, so that Worth
Relation1 has exactly one worth amount and one probability (Figure 10.3).
2. When two binary properties always occur together and ought to be repre-
sented as an
n
-ary relation. For example, Water Pollution in the Isis is low but
increasing. This can be modeled in the same way as the previous example, so
the anonymous class could have an instance Measurement1, with two func-
tional properties has_absolute_measurement and has_trend (Figure 10.4).
3. When the relationship links several objects. For example, Ash Fleet Farm
was sold to Farmer Giles for 250 Merean Schrapnels in 1976. In this case,
there is no clear subject for the
n
-ary relation, so the pattern looks like that
in Figure 10.5.
2 million Merean Schrapnels
worth_amount
is_worth
Ash Fleet Farm
Worth Relation 1
with_probability
High
FIGURE 10.3
n
-ary relations: Ash Fleet Farm is worth 2 million with a high probability.
Low
has_absolute
_measurement
has_measurement
Isis Water Pollution
Measurement 1
has_trend
Increasing
FIGURE 10.4
n
-ary relations: Isis Water Pollution is low but increasing.
Sale 1
has_sale_price
has_sale_item
has_buyer
occurred_in
250 Merean Schrapnels
Ash Fleet Farm
Farmer Giles
1976
FIGURE 10.5
n
-ary relations: Ash Fleet Farm was sold to Farmer Giles for 250 Merean
Schrapnels in 1976.
