Subsumption

We define subsumption, saying that $F$ subsumes $G$, if and only if:

• the type of $F$ is more general than the type of $G$
• if a feature $f$ is defined in $F$ then $f$ is also defined in $G$ such that the value in $F$ subsumes the value in $G$
• if two paths are shared in $F$ then they are also shared in $G$

Consider the following examples of subsumption, where we let < stand for subsumption:

  agr         <  agr
  PERS first     PERS first
                 NUM plu

  sign                phrase                 
  SUBJ agr         <  SUBJ agr 
       PERS pers           PERS first
                           NUM plu

  sign                sign
  SUBJ agr            SUBJ [0] agr
       PERS first          PERS first
       NUM plu     <       NUM plu
  OBJ agr             OBJ [0]
      PERS first
      NUM plu

  false               false              [1] false
  ARG1 false       <  ARG1 [0] false  <  ARG1 [1]
       ARG1 false          ARG1 [0]

Note that the second of these subsumptions holds only if pers is a more general type than first, and sign is a more general type than phrase. It is also important to note that the feature structure consisting simply of the type bot will subsume every other structure, as the type bot is assumed to be more general than every other type.