A unification grammar defined in formalisms such as PATR II and
DCG  usually
defines a relation between a string of words and a logical form.
In sign-based approaches such as UCG  and HPSG  this string of
words is not assigned a privileged status but is the value of one
of the attributes of a feature structure.
I will assume a formalism similar
to PATR II, but without the context-free base; the string is represented
as the value of one of the attributes of a feature structure.
Thus more generally, unification grammars define relations between the values of two (or
more) attributes - for example
the relation between the value of the attributes and
, or between the value of the attributes
and ; these relations are all relations between feature