More thoughts on the documentation for the SAM file format
I recently wrote about how bioinformatics documentation is not always very user-friendly. I made some references to the opaque nature of the official SAM Format Specification (specifically the lack of clarity in explaining the nature of what is in column 2 of a SAM file). After writing this post, I raised an issue on the relevant SAMtools GitHub repository:
I feel that many people have trouble understanding what is meant by bitwise FLAG values. The documentation is very technical and not very transparent to people who may be new to bioinformatics.
Many people might be turning to the documentation after looking at their SAM output file. Maybe they see that their output file has a range of integer values in column 2 and are puzzled by the explanation in the documentation (this is very likely if you have no familiarity with bit patterns).
I think this section would be greatly helped by the following:
- A reminder that the SAM file itself stores an integer value
- An explicit description that a bitwise value of zero means that your read has mapped to the forward strand of the reference
- Some specific examples that explain what various integer values correspond to.
Most of the responses to this were of the form well people can go elsewhere if they want to find better documentation that explains this. E.g.
"There is space on SEQwiki for user created format information."
I accept that the official specification for a file format is not necessarily the same thing as a user guide, but people presumably arrive at the official SAM documentation when searching for help with this kind of thing. E.g. if I search for sam format documentation or sam file format, the top hit is the aforementioned SAM Format Specification.
So the advice seems to be that you don't need to bother making your bioinformatics documentation easy to understand because someone else might come along and do this for you.
