6. A signal-bearing medium tangibly embodying a program of machine-readable instructions executable by a digital processing apparatus to perform a method for transmitting data from a sending device to a receiving device, each device including a processor coupled to a digital data store, the method comprising: the sending device maintaining a dictionary in its digital data store, the dictionary containing multiple data objects each cross-referenced to a different dictionary index code, where the data objects include data objects having one of the following types: a binary graphics file, or a binary executable program; in response to the sending device receiving multiple data objects for transmittal to the receiving device, searching for each of the received data objects in the dictionary contained in the sending device's store; for each data object present in the dictionary, obtaining a representative index code cross-referenced to the data object in the dictionary; and the sending device composing a message to the receiving device, the message including multiple subparts each subpart corresponding to a different one of the received data objects, each subpart comprising: if the corresponding data object is not present in the dictionary, the content of the data object; and if the corresponding data object is present in the dictionary, the index code cross-referenced to the data object; where the composed message further includes one or more flags distinguishing between index codes and non-dictionary data objects in the message.
6. A signal-bearing medium tangibly embodying a program of machine-readable instructions executable by a digital processing apparatus to perform a method for transmitting data from a sending device to a receiving device, each device including a processor coupled to a digital data store, the method comprising: the sending device maintaining a dictionary in its digital data store, the dictionary containing multiple data objects each cross-referenced to a different dictionary index code, where the data objects include data objects having one of the following types: a binary graphics file, or a binary executable program; in response to the sending device receiving multiple data objects for transmittal to the receiving device, searching for each of the received data objects in the dictionary contained in the sending device's store; for each data object present in the dictionary, obtaining a representative index code cross-referenced to the data object in the dictionary; and the sending device composing a message to the receiving device, the message including multiple subparts each subpart corresponding to a different one of the received data objects, each subpart comprising: if the corresponding data object is not present in the dictionary, the content of the data object; and if the corresponding data object is present in the dictionary, the index code cross-referenced to the data object; where the composed message further includes one or more flags distinguishing between index codes and non-dictionary data objects in the message. 10. The medium of claim 6, the method further comprising constructing the dictionary of the sending device and storing the constructed dictionary in the digital store of the sending device, the constructing including forming the dictionary index codes by compressing the cross-referenced data objects according to a predefined compression process.