An n-adic conceptual relation r is said to have a signature of n concept types. The signature is written as <t1, t2, ..., tn>, where t1, t2, t3, etc. are the types of the concepts that are attached to each of the arcs that belong to r.
For example, the relation type
is said to have the signature
This is because the first arc that belongs to Agnt must be attached to a concept whose concept type is either Act or a subtype of Act. The second arc must be attached to a concept whose concept type is either Animate or a subtype of Animate:
Here, "Sing" is a subtype of "Act", which is the first concept in the signature. "Bird" is a subtype of "Animate", which is the second concept in the signature.
The order of the concept types in the signature of a relation is significant and is always constant. This is important for the direction of the arrows on the arcs, as we shall see next.
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