CHAPTER 10
846
Document Interchange
TABLE 10.3 Additional entries in a metadata stream dictionary
KEY
TYPE
VALUE
Type
name
name
(Required)
The type of PDF object that this dictionary describes; must be
Metadata
for a metadata stream.
(Required)
The type of metadata stream that this dictionary describes; must be
XML
.
Subtype
The format of the XML representing the metadata is defined as part of a frame-
work called the Extensible Metadata Platform (XMP) and described in the Adobe
document
XMP: Extensible Metadata Platform
(see the Bibliography). This
framework provides a way to use XML to represent metadata describing docu-
ments and their components and is intended to be adopted by a wider class of ap-
plications than just those that process PDF. It includes a method to embed XML
data within non-XML data files in a platform-independent format that can be
easily located and accessed by simple scanning rather than requiring the docu-
ment file to be parsed.
A metadata stream can be attached to a document through the
Metadata
entry in
the document catalog (see Chapter 3.6.1, “Document Catalog,” and also see
components represented as a stream or dictionary can have a
Metadata
entry (see
TABLE 10.4 Additional entry for components having metadata
KEY
TYPE
VALUE
Metadata
stream
(Optional; PDF 1.4)
A metadata stream containing metadata for the component.
In general, a PDF stream or dictionary can have metadata attached to it as long as
the stream or dictionary represents an actual information resource, as opposed to
serving as an implementation artifact. Some PDF constructs are considered im-
plementational, and hence cannot have associated metadata.
For the remaining PDF constructs, there is sometimes ambiguity about exactly
which stream or dictionary should bear the
Metadata
entry. Such cases are to be
resolved so that the metadata is attached as close as possible to the object that
actually stores the data resource described. For example, metadata describing a
tiling pattern should be attached to the pattern stream’s dictionary, but a shading
should have metadata attached to the shading dictionary rather than to the shad-