Parsing with Constraint-Based Grammars

Question 1

What does it mean for FS1 to subsume FS2?

Answer 1

• Path values: for every path P in FS1 there is a path P in FS2. If P has a value t in FS1, then P also has value t in FS2.
• Path equivalences. Every pair of paths P and Q which are reentrant in FS1 (i.e., which lead to the same node in the graph) are also reentrant in FS2.

Question 2

What is the unification of FS1 and FS2?

Answer 2

The unification of two FSs FS1 and FS2 is defined as the most general FS which is subsumed by both FS1 and FS2, if it
exists.