Once you create a description of your data model, encoding it as a DTD or Schema is the easy part. However for creating your data models in the first place, we recommend that you enlist the aid of an expert as well as plan to invest some time in it yourself. It's just as easy to overdo a data model and make it too complex as it is to omit elements that you'll wish for later.

Thank Goodness Data Modeling Is Over!
What Comes Next?
There are several major areas of design and development in the creation of your XML publishing system. The following paragraphs highlight each of these areas.

• Conversion - You will probably want to convert some of your existing word processing and desktop publishing files to XML. Because conversion tends to be expensive, you should only convert documents that you're continuing to improve or that you're planning to reuse/repurpose for new documents.

  Conversion is expensive because it's complex: you're converting documents with a flat structure that are filled with inconsistencies to files with a hierarchical structure and absolute consistency.

  Some documents are so complex and inconsistent that re-keying is the best approach. Arbortext partners such as Data Conversion Labs (www.dclab.com/) offer such services. On the other hand, your documents may be sufficiently consistent and simple that you can use software to convert automatically or semi-automatically, most likely requiring manual cleanup afterwards. Setting up this software requires creating a "map" between styles and tags. Arbortext, our partners, and other companies offer software and setup services, which the next article in this series will describe in more detail.

• Stylesheets - Because an XML document contains no instructions for formatting its contents for viewing or printing, those instructions have to exist somewhere. That's where stylesheets come in. Stylesheets contain instructions for how to display or print each element (you can learn a lot more at www.arbortext.com/resources/xpn_sep_03.html#tech).

  You'll need stylesheets both for editing and for publishing. Although you could ask your authors to create and edit XML without a stylesheet, they will put up stiff resistance because they will intensely dislike the loss of on-screen formatting because they have grown accustomed to seeing visual cues about the meaning of each element. In other words, they'll want to see the contents of an emphasis tag displayed on the screen in italics instead of just seeing the emphasis tag.

  Without a Stylesheet	With a Stylesheet
  This is <emphasis>very</emphasis> easy!	This is very easy!

• You may need many different stylesheets. You will need one for each different XML editing tool that you use, for each type of document you produce, for each medium to which you publish that document, and for each format variation. For example, if you are producing both print and Web versions of a product catalog and a technical manual, and if you have to produce the print version on both 8 1/2 x 11 and A4 paper, you would need the following stylesheets:
  - Editor stylesheet for catalog
  - Editor stylesheet for technical manual
  - Web stylesheet for catalog
  - Web stylesheet for technical manual
  - Print stylesheet for catalog for 8 1/2 x 11
  - Print stylesheet for catalog for A4
  - Print stylesheet for technical manual for 8 1/2 x 11
  - Print stylesheet for technical manual for A4