com.sun.msv.writer.relaxng

Class RELAXNGWriter

Implemented Interfaces:
Context, GrammarWriter

public class RELAXNGWriter
extends Object
implements GrammarWriter, Context

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

How it works

Grammar object can be thought as a (possibly) cyclic graph made from 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 ElementExp and 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

String
getTargetNamespace()
XMLWriter
getWriter()
void
setDocumentHandler(DocumentHandler handler)
Sets DocumentHandler.
void
write(Grammar g)
Converts this grammar to the XML representation.
void
write(Grammar g, String _defaultNs)
generates SAX2 events of the specified grammar.
void
writeNameClass(NameClass src)

Method Details

getTargetNamespace

public String getTargetNamespace()
Specified by:
getTargetNamespace in interface Context

getWriter

public XMLWriter getWriter()
Specified by:
getWriter in interface Context

setDocumentHandler

public void setDocumentHandler(DocumentHandler handler)
Sets DocumentHandler. This handler will receive the result of conversion.
Specified by:
setDocumentHandler in interface GrammarWriter

write

public void write(Grammar g)
            throws SAXException
Converts this grammar to the XML representation.
Specified by:
write in interface GrammarWriter

write

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

writeNameClass

public void writeNameClass(NameClass src)
Specified by:
writeNameClass in interface Context