| | 189 | === Unary Relationships ===#unary |
| | 190 | |
| | 191 | In the original draft of this page, it was stated that a template definition must have a minimum of two roles. In the discussion below, that was called into question "why not just one"? A relationship that has only a single role, that is, a relationship that connects a thing to nothing else, is called a "unary relationship". |
| | 192 | |
| | 193 | One of the candidate relations to classify a "unary relationship" is a reflexive relation, that is a relation that connects a thing only and always to itself. |
| | 194 | |
| | 195 | Unary relationships can be validly constructed, for example, any binary relationship f(a,b) can be defined as the relation g(a) where, g is defined so that g(x) == f(x,b). |
| | 196 | |
| | 197 | An example might be p(3) where p indicates set membership in prime numbers and 3 is a prime number. You could equally say 3 is an element of p. |
| | 198 | |
| | 199 | In ISO 15926 part 2 terms, p(x) blends several generally distinct concepts together: it includes the concept of class/set membership (classification) and the concept of being a prime number. Similarly entity type and specialization are distinct concepts in part 2. |
| | 200 | |
| | 201 | So apart from expressing set membership, that leaves relations that necessarily link a thing only to itself. While many relations can include elements that are reflexive, that is insufficient. The question that needs to be asked is, are there any relations that are necessarily and always reflexive? |
| | 202 | |
| | 203 | The goal here is to decide: are we imposing too much by disqualifying unary relationships? |
| | 204 | |
