License clarification

[rekado]

Hello,

I'd like to package parasail for GNU Guix, but I'm having difficulties understanding the license. The license looks like a variant of the 4-clause BSD license with the distinguishing difference being:

Redistributions of the software in any form, and publications based on work performed using the software should include the following citation as a reference:

Daily, Jeff. (2016). Parasail: SIMD C library for global, semi-global, and local pairwise sequence alignments. BMC Bioinformatics, 17(1), 1-11. doi:10.1186/s12859-016-0930-z

What does "should" mean here? Is this a recommendation or a legal requirement that goes beyond the usual requirement of acknowledgement that the BSD licenses ask for?

The advertising clause of the original BSD license does not make it a non-free license, but it has the effect of making it incompatible with the GPL (so code under the GPL cannot be combined with code under the original BSD license): https://www.gnu.org/licenses/bsd.html

I'd be happy if you could clarify the meaning of the license.

~~ Ricardo

[jeffdaily]

I am not trained in legal interpretations and how various open source licences interact. The license was produced by the legal team while I was employed at Pacific Northwest National Laboratory (PNNL). Please reach out to them for help here. Thanks.