Word-Level Inverted File Structure

The structure I'm referring to is explained in Witten et al "Managing Gigabytes", where each word in an inverted file is referenced using:

 <2;(1;6,9),(4;8)>

where the (bracketed) terms can be expressed as

(x ; y1, y2, y3, ...)

where x represents the document in which the word exists, and y represents the word position in the document.

The question is, what does the first term in the full structure represent? In each example it is always "2", and I cannot find any reference to it in the book until talking about compression further on, but it is explained in a different context.

Help would be appreciated...

Thanks,

Pete Nayler Received on Wed Oct 11 2000 - 07:50:07 CEST