1. Apparatus for conducting a dialog with a user of at least one computerized enterprise system, the apparatus comprising: an ontological topic definer including a processor using at least one ontological entity to define user dialog topics including items; and a computerized dialog server operative for conducting a dialog with a user of at least one computerized enterprise system about an individual topic from among said user dialog topics, including generating a directed graph based on item references, from links between said items, by applying closure-based variable scoping in conjunction with backward-chaining-based logic to said directed graph, and identifying and scoring potential discussion forks based on said directed graph.