To communicate with the zForce AIR sensor, you need two things: to send/receive messages and to encode/decode the messages.

The sending and receiving you can do in one of the following ways:

• USB HID Touch Digitizer: the sensor can be used as a standard HID Touch Digitizer to report touch data to the OS. For more information, refer to USB HID Transport. 
• USB RAW HID: the sensor uses HID Get and Set Feature Reports as a pipe to read and write. For more information, refer to USB HID Transport
• I2C transport: The sensor's I2C implementation has a certain byte sequence and a signaling system to ensure stability. The sensor takes the role of an I2C slave and has the I2C address 0x50. For more information, refer to I2C Transport.

For the encoding/decoding, you need to understand the structure of the messages and the protocol used to serialize them:

The definition of the protocol message is written in ASN.1 and the communication protocol uses the Distinguished Encoding Rules (DER) to serialize messages.

ASN.1 is a standardized way (ISO/IEC 8824) to describe data regardless of language implementation, hardware system and operation system.
The structure of the zForce AIR messages is defined in the zForce® PDU definition file. For more information, refer to zForce Meassage Specification.

For more details on the zForce serialization protocol, refer to Understanding+the+zForce+ASN1+Protocol.