| 7 | | = Syntax of Discourse Representation Structures (DRSs) = |
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| 8 | | |
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| 9 | | The Prolog syntax of DRSs is defined below in BNF. |
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| 10 | | There are basic and complex DRSs: |
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| 11 | | |
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| 12 | | {{{ |
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| 13 | | <drs> ::= <basic-drs> | |
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| 14 | | <complex-drs> |
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| 15 | | }}} |
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| 16 | | |
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| 17 | | A basic DRS comprises a set of discourse referents and |
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| 18 | | a set of DRS-conditions. Note that all discourse referents and DRS-conditions are prefixed by a |
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| 19 | | list of indices that refer to word positions. |
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| 20 | | |
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| 21 | | {{{ |
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| 22 | | <basic-drs> ::= drs(<referents>,<conditions>) |
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| 23 | | |
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| 24 | | <referents> ::= [] | |
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| 25 | | [<indices>:<referent>{,<indices>:referent>}] |
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| 26 | | |
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| 27 | | <conditions> ::= [] | |
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| 28 | | [<indices>:<condition>{,<indices>:condition>}] |
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| 29 | | |
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| 30 | | <indices> ::= [] | |
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| 31 | | [<number>{,<number>}] |
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| 32 | | |
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| 33 | | <referent> ::= <prolog-atom> | |
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| 34 | | <prolog-variable> |
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| 35 | | }}} |
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| 36 | | |
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| 37 | | Complex DRSs are constructed with the merge |
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| 38 | | (conjoining two DRSs), the sentence-merge (conjoining two DRSs denoting sentences) |
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| 39 | | or with alfa (representing anaphoric or presuppositional information). |
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| 40 | | |
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| 41 | | {{{ |
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| 42 | | <complex-drs> ::= merge(<drs>,<drs>) | |
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| 43 | | smerge(<drs>,<drs>) | |
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| 44 | | alfa(<alfa-type>,<drs>,<drs>) |
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| 45 | | }}} |
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| 46 | | |
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| 47 | | The alfa-type specifies the kind of anaphoric information: anaphoric pronoun, definite description, |
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| 48 | | proper name, reflexive pronoun, or deictic pronoun. |
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| 49 | | |
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| 50 | | {{{ |
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| 51 | | <alfa-type> ::= pro | |
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| 52 | | def | |
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| 53 | | nam | |
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| 54 | | ref | |
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| 55 | | dei |
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| 56 | | }}} |
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| 57 | | |
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| 58 | | |
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| 59 | | There are basic and complex DRS-conditions: |
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| 60 | | |
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| 61 | | {{{ |
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| 62 | | <condition> :: = <basic-condition> | |
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| 63 | | <complex-condition> |
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| 64 | | }}} |
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| 65 | | |
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| 66 | | The basic conditions are one-place properties (predicates), two-place properties (relations), |
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| 67 | | named entities, time-expression, cardinal expressions, or equality: |
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| 68 | | |
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| 69 | | {{{ |
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| 70 | | <basic-condition> ::= pred(<referent>,<symbol>,<pos-type>,<sense>) | |
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| 71 | | rel(<referent>,<referent>,<symbol>,<sense>) | |
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| 72 | | named(<referent>,<symbol>,<ne-type>,<sense>) | |
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| 73 | | timex(<referent>,<time-expression>) | |
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| 74 | | card(<referent>,<number>,<cardinality-type> | |
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| 75 | | eq(<referent>,<referent>) |
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| 76 | | }}} |
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| 77 | | |
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| 78 | | The part of speech type gives more information on the kind of predicate: noun, verb, or |
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| 79 | | adjective/adverb. Note that predicates with the same symbol but with different part of speech type are |
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| 80 | | considered to be different predicates. |
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| 81 | | |
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| 82 | | {{{ |
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| 83 | | <pos-type> ::= n | |
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| 84 | | v | |
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| 85 | | a |
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| 86 | | }}} |
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| 87 | | |
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| 88 | | The sense is denoted by a positive integer (for instance a WordNet sense) or by 0 if |
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| 89 | | the sense is unknown: |
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| 90 | | |
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| 91 | | |
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| 92 | | {{{ |
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| 93 | | <sense> ::= 0 | 1 | 2 | ... |
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| 94 | | }}} |
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| 95 | | |
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| 96 | | Named entity types comprise organsiation, person, title, quoted, location, first name, surname, url, email, or just name when unknown: |
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| 97 | | |
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| 98 | | {{{ |
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| 99 | | <ne-type> ::= org | |
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| 100 | | per | |
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| 101 | | ttl | |
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| 102 | | quo | |
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| 103 | | loc | |
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| 104 | | fst | |
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| 105 | | sur | |
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| 106 | | url | |
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| 107 | | ema | |
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| 108 | | nam |
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| 109 | | }}} |
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| 110 | | |
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| 111 | | The cardinality type is equal, less or equal, or greater or equal. |
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| 112 | | |
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| 113 | | {{{ |
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| 114 | | <card-type> ::= eq | |
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| 115 | | le | |
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| 116 | | ge |
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| 117 | | }}} |
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| 118 | | |
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| 119 | | Time expressions follow more or less the syntax of TimeML. |
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| 120 | | |
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| 121 | | {{{ |
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| 122 | | <time-expression> ::= date(<indices>:<pol>,<indices>:<year>,<indices>:<month>,<indices>:<day>) | |
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| 123 | | time(<indices>:<hour>,<indices>:<minute>,<indices>:<second>) |
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| 124 | | |
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| 125 | | <pol> ::= + | - |
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| 126 | | |
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| 127 | | <year> ::= '0001' | '0002' | ... | '9999' |
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| 128 | | |
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| 129 | | <month> ::= '01' | '02' | ... | '12' |
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| 130 | | |
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| 131 | | <day> ::= '01' | '02' | ... | '07' |
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| 132 | | |
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| 133 | | <hour> ::= '00' | '01' | ... | '23' |
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| 134 | | |
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| 135 | | <minute> ::= '00' | '01' | ... | '59' |
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| 136 | | |
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| 137 | | <second> ::= '00' | '01' | ... | '59' |
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| 138 | | }}} |
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| 139 | | |
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| 140 | | The complex DRS-conditions express disjunction, implication, negation, a question, or |
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| 141 | | a propositional attitude: |
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| 142 | | |
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| 143 | | {{{ |
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| 144 | | <complex-condition> ::= or(<drs>,<drs>) | |
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| 145 | | imp(<drs>,<drs>) | |
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| 146 | | not(<drs>) | |
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| 147 | | whq(<answer-type>,<drs>,<referent>,<drs>) | |
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| 148 | | prop(<refererent>,<drs>) |
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| 149 | | }}} |
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| 150 | | |
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| 151 | | |
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| 152 | | == Example == |
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| 153 | | |
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| 154 | | As an example, consider the DRS for ''Every man loves Mia''. |
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| 155 | | |
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| 156 | | {{{ |
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| 157 | | drs([[4]:Y], |
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| 158 | | [[4]:named(Y,mia,per,0), |
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| 159 | | [1]:imp(drs([[1]:X], |
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| 160 | | [[2]:pred(X,man,n,1)]), |
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| 161 | | drs([[3]:E], |
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| 162 | | [[3]:pred(E,love,v,0), |
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| 163 | | [3]:rel(E,X,agent,0), |
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| 164 | | [3]:rel(E,Y,patient,0)]))]) |
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| 165 | | }}} |
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| 166 | | |
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| 167 | | == Fixed Symbols == |
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| 168 | | |
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| 169 | | There is a set of fixed symbols used in basic DRS conditions. One-place predicates: |
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| 170 | | |
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| 171 | | * topic,a,1 (elliptical noun phrases) |
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| 172 | | * thing,n,12 (used in NP quantifiers: 'something', etc.) |
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| 173 | | * person,n,1 (used in first-person pronouns, 'who'-questions) |
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| 174 | | * event,n,1 (introduced by main verbs) |
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| 175 | | * group,n,1 (used for plural descriptions) |
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| 176 | | * reason,n,2 (used in 'why'-questions) |
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| 177 | | * manner,n,2 (used in 'how'-questions) |
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| 178 | | * proposition,n,1 (arguments of propositional complement verbs) |
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| 179 | | * unit_of_time,n,1 (used in 'when'-questions) |
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| 180 | | * location,n,1 (used in 'there' insertion, 'where'-questions) |
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| 181 | | * quantity,n,1 (used in 'how many') |
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| 182 | | * amount,n,3 (used in 'how much') |
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| 183 | | * degree,n,1 |
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| 184 | | * age,n,1 |
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| 185 | | * neuter,a,0 (used in third-person pronouns: it, its) |
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| 186 | | * male,a,0 (used in third-person pronouns: he, his, him) |
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| 187 | | * female,a,0 (used in third-person pronouns: she, her) |
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| 188 | | * base,v,2 |
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| 189 | | * bear,v,2 |
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| 190 | | |
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| 191 | | Two-place relations: |
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| 192 | | |
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| 193 | | * rel,0 (general, underspecified type of relation) |
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| 194 | | * loc_rel,0 (locative relation) |
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| 195 | | * role,0 (underspecified role: agent,patient,theme) |
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| 196 | | * member,0 (used for plural descriptions) |
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| 197 | | * agent,0 (subject) |
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| 198 | | * theme,0 (indirect object) |
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| 199 | | * patient,0 (semantic object, subject of passive verbs) |
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