SECTION 10.4
849
Page-Piece Dictionaries
TABLE 10.5 Entries in a page-piece dictionary
KEY
TYPE
VALUE
any application name
or well-known data type
dictionary
An application data dictionary (see Table 10.6).
TABLE 10.6 Entries in an application data dictionary
KEY
TYPE
VALUE
LastModified
date
(any)
(Required)
The date and time when the contents of the document,
page, or form were most recently modified by this application.
(Optional)
Any private data appropriate to the application, typically
in the form of a dictionary.
Private
The
LastModified
entry indicates when this application last altered the content of
the page or form. If the page-piece dictionary contains several application data
dictionaries, their modification dates can be compared with those in the corre-
sponding entry of the page object or form dictionary (see Table 3.27 on page 145
and Table 4.45 on page 358), or the
ModDate
entry of the document information
dictionary (see Table 10.2), to ascertain which application data dictionary corre-
sponds to the current content of the page or form. Because some platforms may
use only an approximate value for the date and time or may not deal correctly
with differing time zones, modification dates are compared only for equality and
not for sequential ordering.
Note:
It is possible for two or more application data dictionaries to have the same
modification date. Applications can use this capability to define multiple or extend-
ed versions of the same data format. For example, suppose that earlier versions of an
application use an application data dictionary named
PictureEdit
, and later ver-
sions of the same application extend the data to include additional items not previ-
ously used. The original data could continue to be kept in the
PictureEdit
dictionary
and the additional items placed in a new dictionary named
PictureEditExtended
.
This allows the earlier versions of the application to continue to work as before, and
later versions are able to locate and use the extended data items.