1. A method for placing advertisements on a user interface comprising the steps of: providing a user interface having a plurality of user interface screens, at least some of said plurality of user interface screens containing user-selectable objects; linking said user interface screens together by predetermined paths, wherein each of said plurality of user interface screens can be reached via a predetermined set of said paths; receiving user input resulting in transitions from one of said plurality of user interface screens to a currently displayed another of said user interface screens; wherein a semantic context associated with reaching one of said currently displayed another of said plurality of user interface screens is determined based upon a particular path within said set of predetermined paths taken to reach said currently displayed another of said plurality of user interface screens; and placing at least one advertisement on said currently displayed another of said plurality of user interface screens based on said determined semantic context, wherein said semantic context is further determined based upon contextual relevance, said contextual relevance being calculated by a processor as: HD ⁡ ( q , c ) = ∑ x ∈ { P q - P c } ⁢ ⁢ α r x + ∑ y ∈ { P c - P q } ⁢ ⁢ β r y + ∑ z ∈ { q , c } ⁢ ⁢ γ r z where: α, β, and γ are weighting factors, r n is a hierarchical level of a given topic, and P n is a set of parent topics of an item.