But users need a "tracker" link to find what they're looking for - like the index card in a library catalogue.

但是用户需要tracker服务器来连接他们所要寻找的文件，就像图书馆目录中的索引卡。

youdao

This library has no catalogue, and none of the books has an index or table of contents.

这个图书馆没有书本目录，每本书也没有索引或内容目录。

youdao

A reference from one part of a book, index, catalogue, or file to another part containing related information.

互见参照从书、索引、目录或文件的一部分到另一含有相关资料部分的参照。

youdao

For our part, we're working with rights holders worldwide to index a vast catalogue of programming for online use so hopefully your choices will multiply shortly.

BBC: Digital broadcasting: Industry answers