Designing a markup language is a task similar to designing a building. First, you have to ask some questions: Who am I building it for? How will it be constructed ? How will it be used? Do I give it many small rooms or a few large ones? Will the rooms be generic and interchangeable or specialized? Is there are role for the building, like storage, office space, or factory work? It takes a lot of planning to do it right.
When designing a markup language, there are many questions to answer: What constitutes a document? How detailed do you need it to be? How will it be generated? Is it flexible enough to handle every expected situation? Is it generic enough to support different formatting options and modes? Your decisions will help answer the most basic question which is, how can you represent a piece of information as XML? This problem is part of the important topic of data modeling.
In this chapter, we look at the ways in which different kinds of data are modelled using XML. First, I'll show you the most basic kinds of documents, simple collections of preferences for software applications. The next category covers narrative documents with characteristics such as text flows, block and inline elements, and titled sections. Lastly, under the broad umbrella of "complex" data, I'll talk about the myriad specialized markup languages for everything from vector graphics to remote procedure calls.