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           CHAPTER 10                                                        Document Interchange




                        TABLE 10.3 Additional entries in a metadata stream dictionary
KEY            TYPE         VALUE

Type           name         (Required) The type of PDF object that this dictionary describes; must be Metadata
                            for a metadata stream.

Subtype        name         (Required) The type of metadata stream that this dictionary describes; must be XML.

           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
           implementation note 161 in Appendix H). In addition, most PDF document
           components represented as a stream or dictionary can have a Metadata entry (see
           Table 10.4).

                        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-

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