  The lexical acquisition system presented in this paper incrementally updates
linguistic properties of unknown words inferred from their surrounding context
by parsing sentences with an HPSG grammar for German. We employ a gradual,
information-based concept of ``unknownness'' providing a uniform treatment for
the range of completely known to maximally unknown lexical entries. ``Unknown''
information is viewed as revisable information, which is either generalizable
or specializable. Updating takes place after parsing, which only requires a
modified lexical lookup. Revisable pieces of information are identified by
grammar-specified declarations which provide access paths into the parse
feature structure. The updating mechanism revises the corresponding places in
the lexical feature structures iff the context actually provides new
information. For revising generalizable information, type union is required. A
worked-out example demonstrates the inferential capacity of our implemented
system.
