Abstract: Techniques are disclosed that reduce the computational complexity of PPM-based data compression through use of certain simplifying assumptions that permit faster search for a close-to-optimal PPM model than conventional techniques. The disclosed techniques permit the cost of the computationally-expensive model building task to be amortized over many compression/decompression cycles by maintaining a PersistentModel class, accessible to both the coder and decoder side of the system. This allows the computationally-expensive model building task to be performed only occasionally, as opposed to each time a message is coded. Furthermore, the model-building task is preferably scheduled to run at non-busy times, such that it minimizes user-perceptible service disruptions.

Abstract: A system for providing to a user of a handheld device at least one of location-based information and time-based information includes a server assembly including (1) a server application and a server data storage medium; (2) activity site information periodically updated in the server data storage medium and pertaining to at least one activity site, the activity site information being correspondingly updated in a device data storage medium of the handheld device using a communication link between the handheld device and the server assembly; and (3) a client application on the handheld device adapted to (a) obtain reference location information identifying a reference location; (b) access the activity site information from the device data storage medium; (c) determine a relationship between the activity site information and the reference location, the relationship being at least one of a geographic relationship and a temporal relationship; (d) select at least a portion of the activity site information based on

Abstract: A system for determining a route and presenting navigational instructions therefor preferably includes a plurality of map records including a plurality of business records each identifying a business, a plurality of street records each identifying a street, and a plurality of node records each identifying a node. The system preferably further includes a computation module adapted to execute an algorithm for determining a route between a source location and a destination location using at least one of the map records. The algorithm is preferably adapted to manipulate a graph representation having vertices and edges, wherein each of the vertices corresponds to a respective one of the streets, each of the streets corresponds to exactly one of the vertices, each node corresponds to at least one of the edges, and each edge corresponds to exactly one node.