operator characters

• : (colon), separates optional node identifier from node content;

• [ (left square bracket), separates node properties from outgoing arcs;

• ] (right square bracket), terminates a list of outgoing arcs;

•   (whitespace), separates role labels and values in list of arcs;

• , (comma), separates role–value pairs within list of outgoing arcs;

• + (plus sign), indicates (optional) lemma object property;

• / (slash), indicates (optional) pos property;

• ? (question mark), Lucene-style single-character wildcard;

• * (asterisk), Lucene-style arbitrary sub-string wildcard;

• | (vertical bar), logical disjunction (see below);

• ( and ) (left and right parentheses), grouping of sub-expressions (see below);

• ! (exclamation mark), reserved for negation (to be defined);

• \ (backslash), escape character, suppressing operator status for all of the above.

It is conventional to separate descriptions of different nodes by whitespace, in fact typically even linebreaks; furthermore, the node identifier prefix (indicated by :) is conventionally not separated by white space from the node description. However, unless we find a technical reason to enforce these conventions, we will try to be robust and even allow something like

  x : + terrible[ ARG1 y ]y:crisis[]

There is support for logical disjunction and grouping of sub-expressions, to control the scope of disjunction; by default, disjunction scopes at the highest possible level.

  (
   _light_a_1[ARG1 x]
  |
   _light_n_1[ARG0 y]
   x:compound[ARG1 y]
  )
  x:_bulb_n_1

The logical operators can only be used between nodes, i.e. not inside the description of one node.

What to do about parameterized predicates, e.g. named(Abrams); possibly we can re-purpose the parentheses within the node description.

What to do about case distinctions? Ideally, we would like matching of node and role labels to not be case-sensitive (but parameters like "Abrams" in the above can make case distinctions). Maybe use the first-line Lucene index to normalize case distinctions in labels?