The data content standard specifies the representation of data in all aspects of the tag, reader, and host (i.e. middleware or application program). Because of the limitation of memory capability (storage capacity and communication ability), the data representation in each link must take full account of their own characteristics and adopt different forms of expression. In addition, host access to tags can be independent of the reader and the air interface protocol, that is to say, the reader and the air interface protocol are transparent to the application. The RFID data protocol application interface is based on ASN.1, which provides a set of commands that are independent of applications, operating systems and programming languages, and are independent of the tag reader and tag driver.