## 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 | 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 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 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' |

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 or hash symbol (any information after one of these signs 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).