HTS core package stack
----------------------

  as of August 2015

                   VariantAnnotation
                        |     |
                        v     v
           GenomicFeatures   BSgenome
                        |     |
                        v     v
                      rtracklayer
                           |
                           v
                   GenomicAlignments
                      |         |
                      v         v
     SummarizedExperiment   Rsamtools
                    |       |      |
                    v       v      v
                GenomicRanges   Biostrings
                        |          |
                        v          v
               GenomeInfoDb   XVector
                        |     |
                        v     v
                        IRanges
                           |
                           v 
                       S4Vectors