  The handling of units in an automated way by software systems can be a
cumbersome procedure when the units are parsed as strings. Software systems
parsing units have to take into account extensive tables of unit names, not
always identical between different standards. In the Virtual Observatory
context, the transfer of metadata in access protocols is specially critical for
the understanding of the content of the data (many of which are legacy data).
Driven by this issue, we present a way to handle units automatically which is
based in dimensional analysis considerations. Although the approach presented
here can be valid to any other branch of physics, we concentrate mainly in the
application to spectrum handling in the VO context, and show how the proposed
solution has been implemented in the VOSpec, a tool to handle VO-compatible
spectra.
