XES supports the classifier concept described earlier (Definition 4.2). An XES log defines an arbitrary number of classifiers. Each classifier is specified by a list of attributes. Any two events that have the identical values with respect to these attributes are considered to be equal for that classifier. These attributes should be mandatory event attributes. For example, if a classifier is specified by both a name
attribute and a resource attribute, then two events are mapped onto the same class if their name and resource attributes coincide.