| 术语 | context-sensitive grammar |
| 释义 | context-sensitive grammar 上下文有关文法 A grammar in which each production has the form αAβ→αγβ, where A is a nonterminal and α,β, and γ are arbitrary words with γ nonempty. If γ was allowed to be empty then any type 0 language of the Chomsky hierarchy could be generated. To derive the empty word, a production S→A must also be included, with S not occurring in the right-hand side of any production. The term context-sensitive refers to the fact that A can be rewritten toγ only in the “context”α…β. In a length-increasing grammar each production has a right-hand side at least as long as its left-hand side (apart possibly from S→A). Clearly and context-sensitive grammar is length-increasing, but it can also be shown that any length-increasing grammar is equivalent to a context-sensitive one. 一种文法,其中每个产生式有如下形式:αAβ→αγβ,其中A是非空终结符,α、β和γ是任意的词,且γ是非空串。如果γ允许为空,则可产生Chomsky分级结构的任何0型语言。为了导出空词,必须把下列产生式包括在内:S→AS不出现在任何产生式的右侧。术语“上下文有关”指的是仅在“上下文”α…β中,A可重 写成γ。在长度增加文法中,每个产生式其右侧至少和左侧一样长(撇开可能的S→A)。很显然,任一个上下文有关文法 都是长度增加的,但同样可见,任一个长度增加文法等价于上下文有关的文法。比较context-free grammar。 |
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