An absent word (also called a forbidden word or an unword in other contexts) in 
a sequence is a segment that does not appear in the given sequence. It is a 
minimal absent word if all its proper factors occur in the given sequence. In 
this article, we review the concept of minimal absent words, which includes the 
notion of shortest absent words but is much stronger. We present an efficient 
method for computing the minimal absent words of bounded length for DNA sequence 
using a Trie of bounded depth, representing bounded length factors. This method 
outputs the whole set of minimal absent words and furthermore our technique 
provides a linear-time algorithm with less memory usage than previous solutions. 
We also present an approach to distinguish sequences of different organisms 
using their minimal absent words. Our solution applies a length-weighted index 
to discriminate sequences and the results show that we can build phylogenetic 
tree based on the patent collected information.