We have seen the different bits and pieces needed to define and reference patterns. It's time
to put them all together and create a complete schema. The first exercise is to define
a DTD-like RELAX NG schema which defines each of the elements and its own named pattern.
The full schema could be:
<?xml version="1.0" encoding="UTF-8"?>
<grammar xmlns="http://relaxng.org/ns/structure/1.0"> |
<start>
<ref name="element-library"/>
</start>
<define name="element-library">
<element name="library">
<oneOrMore>
<ref name="element-book"/>
</oneOrMore>
</element>
</define>
<define name="element-book">
<element name="book">
<attribute name="id"/>
<attribute name="available"/>
<ref name="element-isbn"/>
<ref name="element-title"/>
<oneOrMore>
<ref name="element-author"/>
</oneOrMore>
<zeroOrMore>
<ref name="element-character"/>
</zeroOrMore>
</element>
</define>
<define name="element-isbn">
<element name="isbn">
<text/>
</element>
</define> |
<define name="element-title">
<element name="title">
<attribute name="xml:lang"/>
<text/>
</element>
</define>
<define name="element-author">
<element name="author">
<attribute name="id"/>
<ref name="element-name"/>
<optional>
<ref name="element-born"/>
</optional>
<optional>
<ref name="element-died"/>
</optional>
</element>
</define>
<define name="element-name">
<element name="name">
<text/>
</element>
</define> |
<define name="element-born">
<element name="born">
<text/>
</element>
</define>\
<define name="element-died">
<element name="died">
<text/>
</element>
</define>
<define name="element-character">
<element name="character">
<attribute name="id"/>
<ref name="element-name"/>
<optional>
<ref name="element-born"/>
</optional>
<ref name="element-qualification"/>
</element>
</define>
<define name="element-qualification">
<element name="qualification">
<text/>
</element>
</define>
</grammar> |
Or:
grammar{
start = element-library
element-library = element library {element-book +}
element-book = element book {
attribute id { text },
attribute available { text },
element-isbn,
element-title,
element-author+,
element-character*
}
element-isbn = element isbn { text }
element-title = element title {
attribute xml:lang { text },
text
}
element-author = element author {
attribute id { text },
element-name,
element-born?,
element-died?
}
element-name = element name { text }
element-born = element born { text }
element-died = element died { text }
element-character = element character {
attribute id { text },
element-name,
element-born?,
element-qualification
}
element-qualification = element qualification { text }
} |
The DTD style we've just shown is pretty common and
finding the definition of each element in the schema is easy, which
is a great advantage. Another popular style, the content-oriented
style, is to defines content of each element as a separate pattern:
<?xml version="1.0" encoding="UTF-8"?>
<grammar xmlns="http://relaxng.org/ns/structure/1.0">
<start>
<element name="library">
<ref name="library-content"/>
</element>
</start> |
<define name="library-content">
<oneOrMore>
<element name="book">
<ref name="book-content"/>
</element>
</oneOrMore>
</define>
<define name="book-content">
<attribute name="id"/>
<attribute name="available"/>
<element name="isbn">
<ref name="isbn-content"/>
</element>
<element name="title">
<ref name="title-content"/>
</element>
<oneOrMore>
<element name="author">
<ref name="author-content"/>
</element>
</oneOrMore>
<zeroOrMore>
<element name="character">
<ref name="character-content"/>
</element>
</zeroOrMore>
</define>
<define name="isbn-content">
<text/>
</define>
<define name="name-content">
<text/>
</define>
<define name="born-content">
<text/>
</define>
<define name="died-content">
<text/>
</define>
<define name="qualification-content">
<text/>
</define>
<define name="title-content">
<attribute name="xml:lang"/>
<text/>
</define>
<define name="author-content">
<attribute name="id"/>
<element name="name">
<ref name="name-content"/>
</element>
<optional>
<element name="born">
<ref name="born-content"/>
</element>
</optional>
<optional>
<element name="died">
<ref name="died-content"/>
</element>
</optional>
</define>
<define name="character-content">
<attribute name="id"/>
<element name="name">
<ref name="name-content"/>
</element>
<optional>
<element name="born">
<ref name="born-content"/>
</element>
</optional>
<element name="qualification">
<ref name="qualification"/>
</element>
</define>
</grammar> |
Or:
grammar {
start = element library {library-content}
library-content =
element book { book-content } +
book-content =
attribute id { text },
attribute available { text },
element isbn { isbn-content },
element title { title-content },
element author { author-content }+,
element character { character-content }*
isbn-content = text
name-content = text
born-content = text
died-content = text
qualification-content = text
title-content =
attribute xml:lang { text },
text
author-content =
attribute id { text },
element name { name-content },
element born { born-content }?,
element died { died-content }?
character-content =
attribute id { text },
element name { name-content },
element born { born-content }?,
element qualification { qualification }
} |
We will see in Chapter 12: Writing Extensible Schemas that
the style of your schema(Russian doll, DTD like or content-oriented,
as this last schema) has an impact on its extensibility. The last option we've seen
(content-oriented) is the most extensible.
Now let's revisit the "bizarre patterns" mentioned in Chapter 2: Simple Is Beautiful, and shown in Figure�3 shows:
When we think about it, this case is not so uncommon. When
we find it in its original form it's a muddled mess: we have
a first pattern named book-basic with the id attribute and the isbn
and title elements, one or more author elements, an optional character element.
Then we have a second pattern that extends the first one. It's named book-extended and
holds the available attribute and zero or more character elements.
It's confusing to write, certainly, and difficult to follow. Still,
this gives us the opportunity to disentangle the web of confusion.
Updating the "DTD-like" flavor of our schema to reflect
this instance document is just a matter of splitting
up the definition of the book element:
<define name="element-book">
<element name="book">
<ref name="book-basic"/>
<ref name="book-extended"/>
</element>
</define> |
<define name="book-basic">
<attribute name="id"/>
<ref name="element-isbn"/>
<ref name="element-title"/>
<oneOrMore>
<ref name="element-author"/>
</oneOrMore>
<optional>
<ref name="element-character"/>
</optional>
</define> |
<define name="book-extended">
<attribute name="available"/>
<zeroOrMore>
<ref name="element-character"/>
</zeroOrMore>
</define> |
Or, in the compact syntax:
element-book = element book {
book-basic,
book-extended
}
book-basic =
attribute id { text },
element-isbn,
element-title,
element-author+,
element-character?
book-extended =
attribute available { text },
element-character* |
