3. The computing device of claim 2 , wherein the processor is configured to add the particular word to the set of keywords when the weight of meaningfulness is less than a predetermined value, wherein the predetermined value is less than 1.
2. The computing device of claim 1 , wherein selectively adding the particular word comprises adding the particular word to the set of keywords when m≧1 and the weight of meaningfulness is less than 1 and therefore indicates that the document-specific number of occurrences is an unusual event.