1. A method for semantics based video analysis, the method comprising: accepting a description of a monitored scene, the description comprising one or more terms from a plurality of predefined terms; accepting a plurality of rules related to the monitored scene, the rules comprising one or more terms from the plurality of predefined terms; converting the description of the monitored scene into video characterization parameters; receiving video data from a plurality of cameras located at the monitored scene; performing video analysis of the video data based on the video characterization parameters and the rules; converting results of the video analysis into one or more alerts selected from a plurality of predefined alerts; and presenting to a user the one or more alerts.