In a library we classify and catalogue a book after it is acquired and entered in the Accession Register. After cataloguing the book, the entries will be filed in the catalogue. Normally in modern times we maintain a card catalogue. Hence, the entries on the cards will have to be filed at appropriate places in the card catalogue of the library.
In general terms we may say that the entries should be filed immediately after cataloguing the book. But in actual practice we file the entries only after some books are processed. Filing individually for each and every book separately would mean waste of time and energy. Filing may be done once or twice a week after accumulating sufficient number of cards. Till the filing is done the newly processed books may be kept on display.