In the past few years XML has become an important standard for exchanging data in just about any industry. This page gives a brief overview of what XML is and why it is important for prepress.
The topics covered are:
- What is XML?
- XML versus HTML and SGML
- What about those other words: XSL,… ?
- How is XML used in prepress?
- Where can I find more information on XML?
What is XML?
XML is the abbreviation for eXtensible Markup Language. A markup language is a mechanism to identify structures in a document. Take your word processor or layout application as an example: it uses style sheets that allow you to define which part of the document is a header, a sub titles and body text. XML is a similar mechanism that can be used to describe the structure of a document but it is universal and not limited to text only. XML can also be used to define the structure within drawings (e.g. SVG), job tracking systems, e-commerce applications,…
XML has been developed by the W3C, the World Wide Web Consortium. This means that XML has been created to distribute structured documents over the Internet but it can be used for other purposes as well.
The way the structure of a document is described in XML is through the use of tags. If a text document contains a header, it would look like this in XML: text of header . What makes XML so powerful, is the fact that tags are not predefined, you can create your own tags. So if you manage the publications of a chain of book stores, you can create tags like .
XML versus HTML and SGML
XML resembles HTML, the tagging system used to create web pages. The main differences between both systems are the fact that HTML uses a fixed set of tags (without the possibility to add custom tags) and the fact that XML is a much broader standard that can be used for numerous applications.
In fact, XML is a subset of SGML (ISO 8879), a markup language that has already been used for more than 15 years to define the structure within documents. It is mainly used in large organization and government. Compared to SGML, XML is more suited for use on the Internet but any SGML-capable system should also be able to handle XML files.
What about those other words: XSL,… ?
The fact that you can create your own custom tags within XML data makes it a very flexible mechanism. At the same time this limits the usefulness of the standard. How can anything so open be a standard?
This is why a number of standards have popped up that are based on XML but that included a fixed series of tags. This allows systems to exchange structured content using tags that every systems knows how to handle.
One such standard is XSL which defines style sheets using XML.
How is XML used in prepress?
XML has already had a pretty profound impact on the prepress market.
- Repurposing content
One of the things that is made easier by XML is the repurposing of data. Suppose you have a product catalogue that has to be printed as well as put on the Internet or a CD-ROM. If the data are structured using XML and you have both an XML-aware layout application and an XML-aware web design application, less work is needed to publish the data on two completely different media. Nowadays such things are achieved using custom written applications because standard applications like Xpress or InDesign are not yet XML-ready but it is only a matter of time before standard tools will appear on the market.
- Round tripping
XML will also facilitate ’round tripping’. Nowadays, if you create a brochure or another document, this is done in QuarkXPress or another application. Then a separate file is made for putting the document on the web or a CD and another file is made to impose the document. You always have to keep two versions of the document: the original XPress document and the final exchange document (be it PDF, PostScript, EPS or whatever). With roundtripping, there is only one document that can be used both for output as well as for editing the content. FreeHand’s ability of storing its own data within an EPS-file is an example of ’round tripping’ functionality. Illustrator 9 can do a similar thing using PDF. Once a universal technology like XML is used to store the data, you no longer need the original application to edit the document.
- Technologies that use XML
There are a number of technologies that make use of XML:
- SVG is a standard file format for vector based drawings and animation. It is the vendor independent counterpart of Macromedia’s Flash file format. Several prepress applications like Illustrator and Corel Draw can already write SVG files.
- JDF is a file format that is being developed by the CIP4 consortium. It is used to track production related data about complete projects, from their creation through the prepress phase (keeping track of the imposition template used, page order, spot colours,…) and the printing and post printing stage (replacing the current CIP3-file format). For more information on JDF, check this page.
- PPML (Personalised Print Markup Language) is a data format that has been designed for the exchange of data between systems handling variable printing on digital presses. More information can be found on the PODi web site.
Where can I find more information on XML?
There are lots of books on XML but none that focus on prepress (at least as far as I know).
General information on XML can be found on the www.xml.com web site.