The orientation of a CG edges

[lynda souadih]

I have a difficulty to understand  the orientation of a CG edges, and
especially for not binary relations. Somebody can explain me how to
direct the edges of the relation "between" to express the fact that
an object is between two other objects.

I'm waiting for an answer as soon as possible.

Thank you

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[John F. Sowa]

> I have a difficulty to understand  the orientation of a CG edges, and
> especially for not binary relations. Somebody can explain me how to
> direct the edges of the relation "between" to express the fact that
> an object is between two other objects.

The arrows on the arcs of conceptual relations are used in the
CG display form because they're more readable than numbers.
But they use the following convention:

  1. The arrow pointing toward the circle is arc #1.

  2. The arrow pointing away from the circle is arc #2.

When the CG display form is mapped to CGIF, the concepts
or the coreference links are listed in numeric order
following the type label.

For example, the following CG

    [Cat]->(On)->[Mat]

can be represented by the following CGIF:

    [Cat *x] [Mat *y] (On ?x ?y)

For a triadic relation such as Between, the numbers 1, 2, 3 are
used on the arcs in the display form.  The first step is to decide
how to order the three concepts attached to the relation.  The
item between the other two could be placed first, second, or third.
Any ordering is acceptable, but the choice of ordering must be
used consistently.

Following is the CG for "A person is between a rock and a hard place"
with the person in position 3:

    (Betw)-
       <-1-[Rock]
       <-2-[Place]->(Attr)->[Hard]
       ->[Person]

In this notation, the first two arcs are distinguished by the numbers
1 and 2, which point toward the circle.  The third argument could
have the number 3, but it can also be distinguished by having the
third arrow point away from the circle.

The display form, however, is *not* an ISO standard and different
authors draw the diagrams with slightly different notations.  But
CGIF is an ISO standard, and the arcs must be listed in order:

    [Rock *x1] {Place *x2] {Person *x3] [Hard *x4]
    (Betw ?x1 ?x2 ?x3) (Attr ?2 ?x4)

John Sowa


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