In {TAIL ~ systems} that do not support online sales of items, the analysis may be based on one or more other types of user generated events, such as but not limited to item rental events, item rating events, item viewing events, page viewing events, page revisit events, search query submissions, accesses to particular web sites, cell phone usage events, and other types of activities that can be monitored or tracked via {HEAD ~ a computer network} 
In { TAIL ~ systems } that do not support online sales of items , the analysis may be based on one or more other types of user generated events , such as but not limited to item rental events , item rating events , item viewing events , page viewing events , page revisit events , search query submissions , accesses to particular web sites , cell phone usage events , and other types of activities that can be monitored or tracked via { HEAD ~ a computer network }
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