Flexible Data-binding With RelaxNGCC Kohsuke Kawaguchi

2 What ’ s RelaxNGCC?  RelaxNGCC is:  Parser generator (e.g., YACC, JavaCC, or ANTLR)  Data-binding tool (e.g., JAXB, Castor, or Relaxer)  Purpose  To simplify XML parsing development

3 Before RelaxNGCC  But writing SAX handler...  Is hard and tiring  Takes time  Is routine and not fun XML Parser XML document Hand-written SAX Handler So people turn their eyes to data-binding

4 Problems With Data-binding Tools  Impedance mismatch b/w XML and ideal OM  What does (A|B|C)* mean?  Customization is limited  Generated code is low in quality  Expose a lot of unnecessary methods

5 Problems With Data-binding Tools  Unable to bridge existing code and existing schema  Take time to get used to the generated code  Need to know how schemas are mapped

6 After RelaxNGCC  Reduces development time XML Parser XML document Generated SAX Handler Annotated RELAX NG Schema

7 How RelaxNGCC Works?  By associating code and schema number= name= System.out.println("start"); number= System.out.print(number+":"); name= System.out.println(name); System.out.println("end");

8 Key Concepts  Anchoring data to variables Values are copied to specified variables as document gets parsed number=

9 Key Concepts  Code will be also executed at the "right" moment me you start 1:me 2:you end

10 Key Concepts  Pattern blocks work like function calls passing data down and up across boundaries result= j= result= (3); j= i+=Integer.parseInt(j);

11 Code Generation  Each pattern block gets its own class  At runtime, new object is allocated to process new block Class Foo Class Bar

12 Code Generation  Aliases become fields  Additional methods can be defined *** 1 *** *** 2 *** abc = import x.y.z; *** 1 *** class Foo { *** 2 *** String abc;... }

13 Runtime  Code used to help generated code  Just 3 classes  No runtime version dependency  Runtime receives SAX events and coordinate handlers SAX events Generated Runtime Generated SAX Handler Generated SAX Handler Generated Handlers

14 Runtime  Provides services to user-specified code  Retrieve Locator object  Resolve namespace prefix  Redirect sub-tree to another SAX ContentHandler

15 Runtime  User-defined code can be added  Added methods/fields available to handlers  Useful to keep global info SAX events Default Runtime Customized Runtime extend Generated SAX Handler Generated SAX Handler Generated Handlers access

16 Runtime (example) runtime.myFunction();... class MyRuntime extends NGCCRuntime { public void myFunction() {... }

17 Put in Practice  Reading XML configuration file  Extend runtime to hold Options class  Fill in the structure as you go through document name = value= runtime.opt.properties.put( name,value); runtime.opt.paramX = class Options { Properties properties; String paramX; } class MyRuntime : NGCCRuntime { public Options opt; }

18 Put in Practice  Quickly build Abstract Syntax Tree  Just use generated class hierarchy and their fields  Use cc:class to throw in extra classes public Set params; p= name = value= params.add(p); paramX =

19 Put in Practice  Build full-blown object model  RelaxNGCC uses itself to parse RELAX NG  Design OM without worrying about syntax  Then use RelaxNGCC to build a parser for that Good efficient parser in short time

20 Why RELAX NG?  Cannot write annotation like this  How can I anchor 10 values to 10 different variables?  No way!...

21 Why RELAX NG?  Formal model makes RelaxNGCC simple  Simpler state management  Simpler schema parsing  Uniform treatment of attributes/elements

22 Why RELAX NG?  Some XML Schema features don't work well  Nillable  Type substitution  Substitution group... ironic because all those features are supposed to be for data-oriented XMLs

23 Loosely-coupled Systems  Type sharing makes systems tightly-coupled  Some says that's what XML is trying to avoid  Better to share the syntax w/o sharing data model  RelaxNGCC allows you to do this!

24 License  Compiler  GPL  Generated code, including runtime  All yours!

25 To Get More Information  Project web-site   Contact developers   RELAX NG Info   This presentation 

26 End  Acknowledgement  Daisuke Okajima, the inventor of RelaxNGCC  Sun Microsystems, for allowing me to work on RELAX NG  Any Question?