The execution of the rst step described above is straight-
forward. All sub-concepts of `provided activities' are adopted
directly from the 24 local ontologies, resulting in a total of
188 sub-concepts. Due to space concerns, a partial list of
22 sub-concepts (c157 - c178) is included in Figure 1 and
placed in the left column. Each sub-concept is identied
by the ID of its source local ontology and its sequence
number within the local ontology. For example, sub-concept
`History & Culture' c178 D 13(2) is identied by the local
ontology ID `13' and sequence number `(2)' in the local
ontology 13. To achieve the second step described above
(i.e. to organize the sub-concepts into a single multi-level
hierarchy), the reference concepts and new concepts are
derived. Reference activities are normally derived from commonly recognized sources. In this study, these concepts
are obtained from the activity categories published in the
Canadian Travel Survey (CTS), a major survey of the tourism
industry [13]. A total of 20 categories relevant to leisure vacation are selected for this study and they are placed along
the top row in Figure 1.