RELAX NG

First Patterns

In plain English, the document, shown in Example 3-1 can be described as having:

• One library element composed of:

  • One or more book elements having:

    • An id attribute and an available attribute

    • An isbn element composed of text

  • A title element with an xml:lang attribute and a text node

• One or more author elements with:

  • An id attribute

  • A name element

  • An optional born element

  • An optional died element

• Zero or more character elements with:

  • An id attribute

  • A name element

  • An optional born element

  • A qualification element`

The good news—and what makes RELAX NG so easy to learn—is that in its simplest form, RELAX NG is pretty much a way to formalize the previous statements with simple matching rules. Terms described in the plain English description have matching terms in the RELAX NG Schema document that look a lot like XML:

• A “library element” matches <element name="library">...</element>

• An “id attribute” matches <attribute name="id"/>

• “One or more” matches <oneOrMore>...</oneOrMore>

• “Zero or more” matches <zeroOrMore>...</zeroOrMore>

• “Text” matches <text/>

• “Optional” matches <optional>...</optional>

You saw in Chapter 2 that almost every XML structure is a natural pattern for RELAX NG. Further, each RELAX NG element is a pattern; therefore, each RELAX NG pattern matches a structure from the XML document. Let’s now spend some time examining each basic pattern.

The text Pattern

This pattern is the simplest; it simply matches a text node. More precisely, it matches zero or more text nodes. As you’ll ...