The ONE clause in FEKL is used to create a Fact Type with a Mandatory Role Constraint and Internal Uniqueness Constraint.

E.g. The following FEKL statement with a ONE clause creates the Object-Role Model below:

FEKL: 


Object-Role Model:

NB At this stage the Person Entity Type has no Reference Mode and so is in error and coloured red, and similarly the Name Value Type has no Data Type, and so is in error and is red.