Discourse Representation Structure
Discourse Representation Structures (DRSs) can be displayed in different formats. In the PMB we use two different formats: the box format, used for visualisation purposes; and the clause format, used for evaluation purposes.Discourse Representation Structures (box notation)
There are basic and complex DRS-conditions. Terms are either variables or constants. Basic DRS-conditions are defined as follows:
- If SYM is a non-logical symbol, SNS a sense, and x is a term then SYM.SNS(x) is a basic DRS-condition (wordnet concepts);
- If ROL is a symbol denoting a VerbNet role and x and y are terms then ROL(x,y) is a basic DRS-condition (thematic roles);
- If x and y are terms then x=y, x≠y, x≈y, x<y, x>y, x≤y, x≥y, x≺y, x≻y, x⋈y are basic DRS-conditions (comparison operators).
- If B is a DRS, then ¬B, ◇B, and □B are complex DRS-conditions (negation and modals);
- If x is a variable, and B is a DRS, then x:B is a complex condition (propositional);
- If B and B' are DRSs, then B⇒B' and B∨B' are complex conditions (implication and disjunction).
- If D is a (possibly empty) set of discourse referents, and C a (possibly empty) set of DRS-conditions, then <D,C> is a (basic) DRS;
- If B is a (basic) DRS, and B' a DRS, then B↓B' is a (segmented) DRS;
- If U is a set of DRSs, and R a set of discourse relations, then <U,R> is a (segmented) DRS.
Discourse Representation Structures (clause notation)
A DRS in clause notation is an unordered set of clauses that describe a DRS. The first argument of a clause is always a variable for a DRS. The second argument determines the type of the clause. The third and fourth argument are always variables or constants (constants are enclosed in double quotes). The following clauses are permitted:
| Clause Type | Explanation |
|---|---|
| B REF X | DRS B has discourse referent X |
| B NOT B' | DRS B contains DRS-condition ¬ B' (it is not the case that) |
| B POS B' | DRS B contains DRS-condition ◇ B' (it is possible that) |
| B NEC B' | DRS B contains DRS-condition □ B' (it is necessary that) |
| B IMP B' B'' | DRS B contains DRS-condition B' ⇒ B'' (conditional) |
| B DIS B' B'' | DRS B contains DRS-condition B' ∨ B'' (disjunction) |
| B PRP X B' | DRS B contains DRS-condition X : B' (propositional) |
| B SYM SNS X | DRS B contains one-place predicate SYM with sense SNS applied to X |
| B ROL X Y | DRS B contains role ROL that holds between X and Y |
| B REL B' B'' | (segmented) DRS B contains discourse relation REL that holds between DRSs B' and B'' |
| B DRS B' | (segmented) DRS B has DRS B' |
| B EQU X Y | DRS B contains DRS-condition X = Y |
| B NEQ X Y | DRS B contains DRS-condition X ≠ Y (not equal to) |
| B APX X Y | DRS B contains DRS-condition X ≈ Y (approximately equal to) |
| B LES X Y | DRS B contains DRS-condition X < Y (less than) |
| B LEQ X Y | DRS B contains DRS-condition X ≤ Y (less or equal than) |
| B TPR X Y | DRS B contains DRS-condition X ≺ Y (temporally precedes) |
| B TAB X Y | DRS B contains DRS-condition X ⋈ Y (temporally abuts) |
| B SZP X Y | DRS B contains DRS-condition X ∕ Y (spatial above) |
| B SZN X Y | DRS B contains DRS-condition X ∖ Y (spatial under) |
| B SXP X Y | DRS B contains DRS-condition X » Y (spatial behind) |
| B SXN X Y | DRS B contains DRS-condition X « Y (spatial before) |
| B STI X Y | DRS B contains DRS-condition X ⨃ Y (spatial topological inside) |
| B STO X Y | DRS B contains DRS-condition X ᑘ Y (spatial topological outside) |
| B SY1 X Y | DRS B contains DRS-condition X ∥ Y (spatial beside) |
| B SY2 X Y | DRS B contains DRS-condition X ⚮ Y (spatial between) |
| B SXY X Y | DRS B contains DRS-condition X ≖ Y (spatial around) |
The semantic matching tools expects DRSs in clause format with the following technical conventions. They are stored in a simple text file encoded in UTF-8. Each line contains one clause, and clause arguments are separated by one or more spaces or tabs. Comments can be added using a percentage symbol. Any information after this sign is considered to be not part of the clauses. A file can contain more than one DRS, in which case individual DRSs are separated by an empty line (not containing a comment).