The directory $db/pkg is for packages. That is,  
while some software can be installed anywhere,
such as a bin directory, other software 
is best installed in a single directory
containing binaries, documentation, and
data files all in one directoory. 

In BIRCH, wherever possible, I have tried
to keep the bin directory from getting disorganized,
by putting documentation and data files into
separate directory hierarchies. For packages,
this can be accomplished by creating symbolic
links from bin, dat and doc directories to the
package.  Symbolic links also have the
advantage of showing which package a given
file belongs to. 

Packages also offer the advantage of simplifying the 
installation process, keeping things together.
