  Relative compression, where a set of similar strings are compressed with
respect to a reference string, is a very effective method of compressing DNA
datasets containing multiple similar sequences. Relative compression is fast to
perform and also supports rapid random access to the underlying data. The main
difficulty of relative compression is in selecting an appropriate reference
sequence. In this paper, we explore using the dictionary of repeats generated
by Comrad, Re-pair and Dna-x algorithms as reference sequences for relative
compression. We show this technique allows better compression and supports
random access just as well. The technique also allows more general repetitive
datasets to be compressed using relative compression.
