contexts语境contextn.上下文；环境；背景context-freegrammars上下文无关文法context framework model语境框架context-free grammars上下文无关文法context co-occurrence语境共现Context aware computing上下文觉察计算context-free backbone上下文无关主干context-aware service上下文感知业务context-free analysis上下文无关分析contexts and situations语篇与情境context-free language上下文无关语言