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Topic: Incremental Updates Question
Conf: (P-PDF) Developers, Msg: 107277
Date: 3/8/2004 09:04 PM
When an incremental update is done, the trailer prev field points to the previous cross section reference. what happens to the first trailer prev
assume there was only a single trailer earlier.
the PDFReference describes that there may be multiple copy of the object across the file because of incremental update. when an incremental update is done, the newly added cross reference section has entries of the objects updated or changed or deleted, how come a copy of the entry is generated. if an object is updated its generation number is suppose to be updated so there can't be a copy. i m utterly confused about it.
any help will be greatly appriciated
*********** PDFReference Para ******
Because updates are appended to PDF files, it is possible to end up with several
copies of an object with the same object identifier (object number and generation
number). This can occur, for example, if a text annotation (see Section 8.4,
“Annotations”) is changed several times, with the file being saved between changes.
Because the text annotation object is not deleted, it retains the same object
number and generation number as before. An updated copy of the object is included
in the new update section added to the file; the update’s cross-reference
section includes a byte offset to this new copy of the object, overriding the old
byte offset contained in the original cross-reference section. When a viewer application
reads the file, it must build its cross-reference information in such a way
that the most recent copy of each object is the one accessed in the file.