Definition 1. (data format and data) 
        Data formats are defined recursively as follows :

• A bit (f_b), a character (f_c) and an integer (f_i) are data formats.
• If  f₁,f₂,...,f_n are data formats,    f₁...f_n is a data format.
• If a data format f = f₁...f_n  , f[i] denotes the ith component of  f
• The data value d on the data format  f is represented as d(f).
• d(f)[i] denotes the ith component of the data d(f).

  Example

• f1 =   fi fc fc fi fi is a data format.
• f2 = fi f1 f1 is also a data format.
• f1[2] = fc and f2[2] = f1.
• A sequence "34 'T' 'H' 59 11" is a data format on f1.
• d(f1)[1] = 34 and d(f1)[2] = 'T'.