相似的，像ISBN、OCLC控制号、LCCN以及图书馆条码号这些“识别符”都是重要的字符串，它们都是识别的指示符，但是作用的大小各有不同。

Similarly, "identifiers" such as ISBN, OCLC number, LCCN, and library barcode number are used as key strings but are only identity indicators with varying strengths.

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文章通过对主要字段指示符的取值分析，指出了指示符的重要作用以及文献著录中应注意的问题。

By analyzing the value of primary field indicator, this article points out important function of indicator and problems in document bibliography.

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