The value unordered for the ordering property signifies that instances of the classifiers at the target end of the association are not ordered. This is the default value for this property and if a value for the property is not specified then the value by default is unordered. The multiplicity at the target end must be greater than one since a value of one or less would specify a set with one or less elements, for which ordering would be meaningless.
Explanation
The value unordered simply means that the order of instances of the classifier at the target end (near end) is not specified and that any operations on the source (far end) classifier have no responsibility to maintain order.
An association end is related to the value unordered, which specifies the ordering property, because this attribute is added to an association end to increase the precision of the semantics, describing an aspect of the way the classifier participates in the association relationship.
