com.sun.msv.writer.relaxng

Class RELAXNGWriter

public class RELAXNGWriter extends Object implements GrammarWriter, Context

converts any Grammar into RELAX NG XML representation through SAX1 events.

How it works

{@link Grammar} object can be thought as a (possibly) cyclic graph made from {@link Expression}. For example, the following simple TREX pattern will be represented as following AGM.


 <grammar>
   <start name="X">
     <element name="foo">
       <choice>
         <string> abc </string>
         <ref name="Y" />
       </choice>
     </element>
   </start>
   <define name="Y">
     <element name="bar">
       <string> abc </string>
       <optional>
         <ref name="X" />
       </optional>
     </element>
   </define>
 </grammar>
 

Note that

To write these expressions into TREX XML representation, we have to take care of cycles, since cyclic references cannot be written into XML without first cut it and use <ref>/<define> pair.

First, this algorithm splits the grammar into "islands". Island is a tree of expressions; it has a head expression and most importantly it doesn't contain any cycles in it. Member of an island can be always reached from its head.

TREXWriter will make every {@link ElementExp} and {@link ReferenceExp} a head of their own island. So each of them has their own island.

It is guaranteed that this split will always give islands without inner cycles. Several islands can form a cycle, but one island can never have a cycle in it. This is because there is always at least one ElementExp in any cycle.

Note that since expressions are shared, one expression can be a member of several islands (although this isn't depicted in the above figure.)

Then, this algorithm merges some islands. For example, island E is referenced only once (from island D). This means that there is no need to give a name to this pattern. Instead, island E can simply written as a subordinate of island D.

In other words, any island who is only referenced at most once is merged into its referer. This step makes the output more compact.

Next, TREXWriter assigns a name to each island. It tries to use the name of the head expression. If a head is anonymous ReferenceExp (ReferenceExp whose name field is null) or there is a name conflict, TREXWriter will add some suffix to make the name unique.

Finally, each island is written as one named pattern under <define> element. All inter-island references are replaced by <ref> element.

Why SAX1?

Due to the bug and insufficient supports for the serialization through SAX2, The decision is made to use SAX1. SAX1 allows us to control namespace prefix mappings better than SAX2.

Author: Kohsuke KAWAGUCHI

Method Summary
StringgetTargetNamespace()
XMLWritergetWriter()
voidsetDocumentHandler(DocumentHandler handler)
voidwrite(Grammar g)
voidwrite(Grammar g, String _defaultNs)
generates SAX2 events of the specified grammar.
voidwriteNameClass(NameClass src)

Method Detail

getTargetNamespace

public String getTargetNamespace()

getWriter

public XMLWriter getWriter()

setDocumentHandler

public void setDocumentHandler(DocumentHandler handler)

write

public void write(Grammar g)

write

public void write(Grammar g, String _defaultNs)
generates SAX2 events of the specified grammar.

Parameters: defaultNs if specified, this namespace URI is used as "ns" attribute of grammar element. Can be null.

Throws: IllegalArgumentException If the given grammar is beyond the expressive power of TREX (e.g., some RELAX NG grammar), then this exception is thrown.

writeNameClass

public void writeNameClass(NameClass src)