Types vs. Sorts in HPSG

[Mark Johnson]

> To me "type" and "sort" are synonyms, at least in the context
> of feature structures.
>
> Carl

"Type" and "sort" are often used as synonyms, but I think that it
makes sense to distinguish them the way that some logicans do:

"sort" refers to a semantic distinction, where the objects that the
language describes are segregated into several kinds or sorts.

"type" refers to a syntactic distinction, where expressions from
the language are separated into different categories or types.

I think the standard view about feature structures is that the
relevant distinction is semantic.  Following the terminological
suggestion I just made, we'd say that the objects are sorted, but that
the description language is untyped.  Indeed, descriptions in which
type clashes occur are not viewed as having violated the syntax of
descriptions (which is what they would be if they were ill-typed),
rather they just denote the empty set.  (Lots of other systems are
formulated this way; e.g. LISP, which is sorted but untyped).


However, to aid the development and maintainance of large grammars I
think it _would_ make sense to impose type constraints.  If the
grammar contains certain obvious type clashes, then I think it would
be useful for the grammar development environment to identify these to
the grammar writers as syntactic errors (the way a compiler does),
rather than just silently fail!

Best

Mark