In a one-to-one relationship, one record in a table is associated with one and only one record in another table.
For example, in a school database, Consider there are 2 schema 'student' and 'Contact info'. each student has one record associated in the Contact Info' schema. So it is 1:1 cardinality.
In the schema element syntax for defining 1:1 cardinality, use revCardinality = 'single'