11. A method performed by a computer server for inferring location context categories for a set of mobile users having at least two members, comprising: for each mobile user in the set, receiving at least one location context category from one or more mobile web applications responsive to a respective query; and applying multi-user collaborative machine learning with an objective function to the at least one location context category for each mobile user in the set to infer a single refined location context category for each mobile user in the set to form a matrix.
15. The method of claim 11 , further comprising, for at least one mobile user in the set, inferring at least one future intention of the at least one mobile user based on the single refined location context category.