Now, what do we learn from this? It seems like there may be some serious problems with this grammatical approach to language.
And I want you to tell me which of these you think are serious problems, true or false.
So, one issue is, is it easy to write a grammar that will emit good parses accidentally? Tell me if that's true or false.
Is it easy to write a grammar that will include spurious parses, or bad parses?
Is that true or false? And trees are unobservable compared to words, which are observable. Is that a problem, true or false?
And then let's look at some possible solutions. Now, one possibility would be,
if we have too many parses to deal with, and we don't know which ones should be the right ones,
maybe we should associate a probability with each tree.
Is that a good idea? True or false?
Secondly, if words are put together that don't seem to make sense, maybe we should bring back word association statistics,
like we had in the Markov models, and incorporate them into the tree models? Is that a good idea, true or false?
And finally, if we have the problem of ambiguity of our trees, maybe we should make the grammar unambiguous.
After all, that's what we do with our programming languages. We make our programming languages unambiguous,
so that, for example, A plus B times C, we know, is parsed as if it had parentheses around the B and C,
and is not ambiguous as to whether it could be parsed the other way.
Would it be a good idea to make our grammar unambiguous?
この文法的な言語処理へのアプローチには 重大な問題があるかもしれません
では次のうちどれが重大な問題か 真か偽で答えてください
1つ目は“よい構文解析の選択肢を 誤って除外する文法を記述しやすい”
これは真か偽のどちらでしょう？
“誤りのある構文解析つまり悪い構文解析を 含む文法を記述しやすい”
真か偽のどちらでしょう？
“観察可能な単語と比べ 木が直接観察できないことは問題である”
こちらの真偽は？
次は考えられる解決方法を見ていきましょう 1つ目の解決策は
“構文解析が何通りもあり どれが正しいか分からない場合は”
“それぞれの木の確率で考えるとよい”
これはよい解決方法ですか？ 真か偽で答えてください
2つ目は“組み合わさった語が 意味を成さない場合はマルコフモデルのような”
“連想語の統計を木のモデルに用いるとよい” これは真か偽のどちらでしょう？
最後は“木の多義性の問題が生じた場合は 文法を一義的にするとよい”です
これはプログラミング言語で実行されています プログラミング言語は一義的です
例えばa＋b×cの式にはbとcを 囲む括弧があると考えて構文解析を行い
他の構文解析があるか迷わないようにします
さて文法を一義的にすることは よい解決策でしょうか？