SECTION F.4
1051
Access Strategies
ITEM
SIZE (BITS)
DESCRIPTION
5
See Table F.3, item 11
A bit-packed list of shared object identifiers; that is, indices into the shared
object hint table (see Section F.3.2, “Shared Object Hint Table”). Item 4 for
this group specifies how many shared object identifiers are associated with
the group.
F.4 Access Strategies
This section outlines how the client can take advantage of the structure of a
Linearized PDF file to retrieve and display it efficiently. This material is not for-
mally a part of the Linearized PDF specification, but it may help explain the ratio-
nale for the organization.
F.4.1 Opening at the First Page
As described earlier, when a document is initially accessed, a request is issued to
retrieve the entire file, starting at the beginning. Consequently, Linearized PDF is
organized so that all the data required to display the first page is at the beginning
of the file. This includes all resources that are referenced from the first page, re-
gardless of whether they are also referenced from other pages.
The first page is usually but not necessarily page 0. If the document catalog con-
tains an
OpenAction
entry that specifies opening at some page other than page 0,
that page is the one physically located at the beginning of the document. Thus,
opening a document at the default place (rather than a specific destination) re-
quires simply waiting for the first-page data to arrive; no additional transactions
are required.
In an ordinary PDF viewer application, opening a document requires first posi-
tioning to the end to obtain the
startxref
line. Since a Linearized PDF file has the
first page’s cross-reference table at the beginning, reading the
startxref
line is not
necessary. All that is required is to verify that the file length given in the lineari-
zation parameter dictionary at the beginning of the file matches the actual length
of the file, indicating that no updates have been appended to the PDF file.
The primary hint stream is located either before or after the first-page section,
which means that it is also retrieved as part of the initial sequential read of the
file. The client is expected to interpret and retain all the information in the hint