From Genome Analysis Wiki
→Decompose biallelic block substitutions
There is now an additional option -a which decomposes non block substitutions into its constituent SNPs and indels. (kindly added by [[https://github.com/holtgrewe holtgrewe@github]]) <br>
There is no exact solution and this decomposition is based on the best guess outcome using a Needleman-Wunsch algorithm. <br>
You might also want to check out [https://github.com/vcflib/vcflib#vcfallelicprimitives vcfallelicprimitives].