## 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).
The complex DRS-conditions are defined as follows:
• 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).
A DRS is defined as follows:
• 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 TypeExplanation
B REF XDRS 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 XDRS B contains one-place predicate SYM with sense SNS applied to X
B ROL X YDRS 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 YDRS B contains DRS-condition X = Y
B NEQ X YDRS B contains DRS-condition X ≠ Y (not equal to)
B APX X YDRS B contains DRS-condition X ≈ Y (approximately equal to)
B LES X YDRS B contains DRS-condition X < Y (less than)
B LEQ X YDRS B contains DRS-condition X ≤ Y (less or equal than)
B TPR X YDRS B contains DRS-condition X ≺ Y (temporally precedes)
B TAB X YDRS B contains DRS-condition X ⋈ Y (temporally abuts)
B SZP X YDRS B contains DRS-condition X ∕ Y (spatial above)
B SZN X YDRS B contains DRS-condition X ∖ Y (spatial under)
B SXP X YDRS B contains DRS-condition X » Y (spatial behind)
B SXN X YDRS B contains DRS-condition X « Y (spatial before)
B STI X YDRS B contains DRS-condition X ⊍ Y (spatial topological inside)
B STO X YDRS B contains DRS-condition X ⊍ Y (spatial topological outside)
B SY1 X YDRS B contains DRS-condition X ∥ Y (spatial beside)
B SY2 X YDRS B contains DRS-condition X ⚮ Y (spatial between)
B SXY X YDRS 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).