What is SONAME in port builds?

[Montgomery-Smith, Stephen]

I am trying to build the port graphics/opendx, and at the qa stage it says:

Error: /usr/local/dx/bin_freebsd/builder is linked to
/usr/local/lib/libcdf.so which does not have a SONAME.
science/cdf needs to be fixed.

What does this mean, and how do I fix it?

BTW I am maintainer of both ports.