Technical Q & A
This Q & A attempts to define variable data printing and to describe how pdfExpress™ can help you better communicate with your customers.
What is Variable Data Printing?
What is Lexographic Imaging?
What is Variable Data Lexography?
How is PDF used in Variable Data Lexography?
How is the PDF paradigm extended to include variability?
How does pdfExpress™ work?
How is a document "marked-up" for use in variable data printing?
How is the pdfExpress™ product defined?
What is Variable Data Printing?
Variable data printing is the process of merging information, in the form of text or graphics, from one or more information sources with one or more background pages. The canonical example of variable data printing is a form letter where the name and address of the recipient changes on each letter but the letter body remains the same.
Variable data printing is not, however, limited to simple, one-page form letters. A more comprehensive definition of variable data printing is "the process whereby a series of one or more documents is generated by merging background information common to an entire series of documents with specific information which differentiates each document within the series." The differentiation is derived from the content that is merged with the base document.
This definition is general enough to also encompass the processes of on-demand printing and automated document construction, which are merely special cases of variable data printing. Variable data printing can be achieved through a wide range of processes, which can be software based, hardware base, or some combination of both.
What is Lexographic Imaging? top
Lexographic imaging is the process of performing variable data printing via software or hardware by converting a textual description of an image via a rendering process into a graphic image. This process typically takes as input ASCII text and renders output either on a computer display or directly onto paper, e.g., via a laser printer, or film, e.g., via a photo-typesetter.
You are probably most familiar with lexographic imaging as HTML, PostScript or PDF.
Lexographic imaging can be used to describe the process a browser uses when rendering HTML onto a display. Similarly, it also describes the process a PostScript printer uses to render the PostScript file onto a page and the process a PDF viewer uses to render PDF onto a screen. For the purposes of definition, we define a "Lexographic Language" to be a structured, textual language that is means to describe via text a graphic rendering process. Thus HTML, PostScript and PDF are all lexographic languages.
What is Variable Data Lexography? top
Variable data lexography is the specific subset of variable data printing in which documents are defined by a lexographic language, e.g., HTML, PDF or PostScript, for the variable data printing process.
How is PDF used in Variable Data Lexography? top
Today PDF is used almost exclusively as a static representation for documents. PDF documents, once created, have a life, which consists almost entirely of being viewed, either through a PDF reader such as Acrobat Reader, a web browser or GhostScript. Therefore, most users today are familiar with PDF documents only through their appearance on the computer screen.
With pdfExpress we extend the familiar paradigm of viewing static PDF documents on a screen to include variability. To accomplish this we provide a logical and clear extension to the familiar paradigm.
How is the PDF paradigm extended to include variability? top
First, we allow any PDF document, without change, to work as the basis for variability, regardless of who created it or how it was created.
Second, we extend the existing Acrobat Exchange interface to add a single tool. This tool, the "express" tool, is used exclusively to define variability. With this tool we allow the user to select objects on the PDF page and to control their variability attributes.
Third, documents which have been modified for variability, retain the added variability information such that the PDF file remains fully compatible with the PDF standard as published by Adobe. This means that any document marked for variability by pdfExpress still remains, first and foremost, a purely PDF document.
Finally, we define the merging process of combining data with PDF pages through an application, which is separate, though dependent and interactive with, Acrobat Exchange. This co-dependent user interface model means that Acrobat is extended by an additional application that does not change the basic Acrobat user interface paradigm, but which works with Acrobat to provide the added functionality of merging data. This means that users who wish to define variability in Acrobat can do so without having to learn the merging process, while, at the same time, users who wish to perform the complete range of markup and merge need only to learn the additional functionality provided by pdfExpress.
How does pdfExpress work? top
pdfExpress allows any page in any PDF document to be used as a background (or template) in a variable data printing application. Users can use multiple pages from one or many documents as backgrounds. Backgrounds can vary in media size and orientation.
The basic variable data printing process involves creating an output document assembled from one or more pages taken from "background" documents. Pages are added to the output document in groups of one or more. As each page set is added to the output document variable text and graphic elements may be applied to the page or pages. This application of text and graphics to a page is controlled by the placement of special marks that control the details of how the copying occurs for a given textual or graphic element.
How is a document "marked-up" for use in variable data printing? top
During the copy process textual or graphic items that are marked on the background page cause certain exceptions during the copy process. There are three basic types of exceptions that can occur during the copy process.
The first exception, invisibility, is very simple. The user may require that some elements that appear in the original "background" document should not appear in the output document. Such elements may be marked with the invisibility property and, when the page is copied from the background to the output document, such elements will not appear.
The second exception, variability, is also very simple. Variability involves a one-to-one substitution of a textual or graphic element as the page is copied from the background to the output document. The addition occurs wherever the variability property is placed on an element in the background document.
Note that variability does not imply invisibility and that to replace a marked item the item must be marked with both the invisibility and variability properties.
The third exception, iteration, is a process that extends variability. Iteration is used where multiple text or graphic elements must be added to a document such that the placement of elements subsequent to the first element are positionally related to the location of an initial element.
For example, if we wish to add an address block to a letter, we identify the address block by identify the initial element of the address block, e.g., the city-state-zip line, and by identifying the second element as the line directly above the city-state-zip line. The relationship of these two elements defines the iteration and defines how the elements will be placed graphically on the page. In this case the address block grows upward from the initial city-state-zip line.
pdfExpress extends this model to include iteration in any direction of single elements as well as iterations of iterations. Iteration can occur whenever an item (or iteration group) marked for variability is linked to another marked item. This linking is referred to as an iteration group. An iteration group may involve only textual or only graphical elements - it may not involve mixed textual and graphical elements.
How is the pdfExpress product defined? top
pdfExpress is a technology suite that allows the Adobe Acrobat Exchange user to create, control and manage a complete PDF-based variable data printing environment. This environment supports not only the variable data printing process, but also allows that process to interact with existing printing technologies and industry standard software such as Java, COM, AppleEvents, web, and SQL databases. pdfExpress is defined by an object-component architecture. This architecture allows each element of pdfExpress, from Acrobat itself to third party applications, to be its own, completely separate application.
Each pdfExpress component communicates with other pdfExpress components via a platform neutral, PDF-based protocol. This protocol is transmitted between the various components via one or more industry standard communications architectures such as Java RMI, CORBA, and COM. The core of pdfExpress is pdfExpress.api. This is a standard Acrobat Exchange plug-in which defines all of the core variable data and information transfer capabilities used by the remaining components.
Within the pdfExpress plug-in there are two distinct interfaces. The first, pdfAuthor, is the interaction model for variable data mark up as described above. This model is completely self contained within the plug-in and is independent of the merge process. Any user possessing this plug in can open, create, edit, mark-up and save documents, which include the pdfExpress variable data capabilities.
The second interface, pdfMerge, is exposed in two ways. First, through a COM or AppleEvent interface similar to the IAC Acrobat interface. Second, tthrough a bidirectional software buss architecture called DataBuss. The DataBuss provides a standardized extension point to COM and AppleEvents to extend their reach to other, non-Microsoft and non-Apple platforms so that platforms such as Unix can participate in pdfMerge functionality.
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