The present invention can be used in a natural language processing system (100) to determine a relationship (such as similarity in meaning) between two textual segments. The relationship can be identified or determined based on logical graphs (e.g. figures 3B, 3C) generated from the textual segments. A relationship between first and second logical graphs (figures 3B, 3C) is determined. This is accomplished regardless of whether there is an exact match between the first and second logical graphs (FIGS. 3B, 3C). In one embodiment, the first graph (figure 3B) represents an input textual discourse unit. The second graph (figure 3C), in one embodiment, represents information in a lexical knowledge base (LKB) (106). The input graph can be matched against the second graph, if they have similar meaning, even if the two differ lexically or structurally. |