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                                               1055
      SECTION F.4                                                           Access Strategies



F.4.5 Following an Article Thread

      As indicated earlier, the bead dictionaries for any article thread that visits a given
      page are located with that page. This enables the bead rectangles to be activated
      and proper cursor feedback to be shown.

      If the user follows a thread, the viewer application can obtain the object number
      from the N or P entry of the bead dictionary. This identifies a target bead, which
      is located with the page to which it belongs. Given this object number, the viewer
      application can go to that page, as discussed in Section F.4.3, “Going to Another
      Page of an Open Document.”


F.4.6 Accessing an Updated File

      As stated earlier, if a Linearized PDF file subsequently has an incremental update
      appended to it, the linearization and hints are no longer valid. Actually, this is not
      necessarily true, but the viewer application must do some additional work to val-
      idate the information.

      When the viewer application sees that the file is longer than the length given in
      the linearization parameter dictionary, it must issue an additional transaction to
      read everything that was appended. It must then analyze the objects in that up-
      date to see whether any of them modify objects that are in the first page or that
      are the targets of hints. If so, it must augment its internal data structures as neces-
      sary to take the updates into account.

      For a PDF file that has received only a small update, this approach may be worth-
      while. Accessing the file this way is quicker than accessing it without hints or re-
      trieving the entire file before displaying any of it.

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