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一文献标题是自然语言,结构形式多数是偏正式短语,也有的是句子。主题词在短语或句中充当什么成份是不固定的,也就是说,它在短语或句中的位置存在着不定性。因此,单靠语法和传统逻辑来分离主题词可能难以奏效,还需要求助于现代逻辑。科技文献标题输入后,成了二进位数的代码,它包含若干单词的代码(主题词是其中之一)。整个标题的代码是全集(universal set),而单词的代码是它的子集(subset)。假若数据库
A document title is a natural language, most of the formal structure is a partial phrase, but also some sentences. The keyword is not fixed in the phrase or sentence, that is to say, it is uncertain in the position of the phrase or sentence. Therefore, the separation of thematic terms by grammar and traditional logic alone may not be effective and will require recourse to modern logic. After the scientific literature title has been entered, it becomes the binary code, which contains code for several words (the subject keyword is one of them). The entire title’s code is a universal set, and the word’s code is a subset of it. If the database