Creating reusable well-structured pdf as a sequence of component object graphic (cog) elements

Portable Document Format (PDF) is a page-oriented, graphically rich format based on PostScript semantics and it is also the format interpreted by the Adobe Acrobat viewers. Although each of the pages in a PDF document is an independent graphic object this property does not necessarily extend to the components (headings, diagrams, paragraphs etc.) within a page. This, in turn, makes the manipulation and extraction of graphic objects on a PDF page into a very difficult and uncertain process. The work described here investigates the advantages of a model wherein PDF pages are created from assemblies of COGs (Component Object Graphics) each with a clearly defined graphic state. The relative positioning of COGs on a PDF page is determined by appropriate "spacer" objects and a traversal of the tree of COGs and spacers determines the rendering order. The enhanced revisability of PDF documents within the COG model is discussed, together with the application of the model in those contexts which require easy revisability coupled with the ability to maintain and amend PDF document structure.

Extracting reusable document components for variable data printing

Variable Data Printing (VDP) has brought new flexibility and dynamism to the printed page. Each printed instance of a specific class of document can now have different degrees of customized content within the document template. This flexibility comes at a cost. If every printed page is potentially different from all others it must be rasterized separately, which is a time-consuming process. Technologies such as PPML (Personalized Print Markup Language) attempt to address this problem by dividing the bitmapped page into components that can be cached at the raster level, thereby speeding up the generation of page instances. A large number of documents are stored in Page Description Languages at a higher level of abstraction than the bitmapped page. Much of this content could be reused within a VDP environment provided that separable document components can be identified and extracted. These components then need to be individually rasterisable so that each high-level component can be related to its low-level (bitmap) equivalent. Unfortunately, the unstructured nature of most Page Description Languages makes it difficult to extract content easily. This paper outlines the problems encountered in extracting component-based content from existing page description formats, such as PostScript, PDF and SVG, and how the differences between the formats affects the ease with which content can be extracted. The techniques are illustrated with reference to a tool called COG Extractor, which extracts content from PDF and SVG and prepares it for reuse.