User-defined relationships between individuals
In ISO 15926-2 you will find a number of pre-defined relationships, like connection_of_individual. These will, presumably, be used most often, but they do not cover all situations in real life. So, in order not to get stuck, Part 2 offers a way to use an instance of Other Relationship in combination with with a ClassOfRelationshipWithSignature that can be used to classify the new relationship you have in mind.
WARNING - Do not use this lightly, because it may turn out to be nonsensical and the exchange of information may fail for that reason.
These templates apply, first one for the definition of the instance of ClassOfRelationship WithSignature, and then one for the OtherRelationship:
John and Mary Doe have a heterosexual monogamous marriage relationship
The above templates assume dual participation. There is also a template that assumes one participation and one involvement_by_reference: