[x3d-public] General-purpose VRML parsing motivations; Comparison of parser generators - Wikipedia

[Don Brutzman]

The working group has been talking about possible ways to take advantage of the formal grammars for VRML syntax:

	19776-2 Extensible 3D (X3D) encodings Part 2: Classic VRML encoding
	Annex A (normative) Grammar
	http://www.web3d.org/documents/specifications/19776-2/V3.3/Part02/grammar.html

	14772 Virtual Reality Modeling Language (VRML97)
	Annex A (normative) Grammar definition
	http://www.web3d.org/documents/specifications/14772/V2.0/part1/grammar.html

It would be interesting to generate a state-machine diagram for parsing the VRML grammar.  Perhaps one already exists somewhere?

There are of course many converters and parsing libraries for VRML/X3D.  Many open-source code APIs exist, though they tend to be specifically tied to implementation goals (such as rendering in a player).

	X3D Resources: Conversions and Translation Tools
	http://www.web3d.org/x3d/content/examples/X3dResources.html#Conversions

Am hoping that is we can create a simple VRML -> X3D importer, we might include it in various X3D SAI open-source implementations (like X3DJSONLD and X3DJSAIL).  If it is simple code/pseudocode, then it would be straightforward to maintain across each of these programming languages: JavaScript, Java, C, C++, C#, Python, and others (e.g. ObjectPascal).

	X3D Specification Relationships (draft)
	http://2014.web3d.org/specifications/X3dSpecificationRelationships.2017August11.png

Wikipedia has an interesting page comparing grammar parsers:

	https://en.wikipedia.org/wiki/Comparison_of_parser_generators

Perhaps ANTLR might be useful for parsing the VRML grammar and generating parsers?  Multilingual support is provided.

Language-lawyer point:  the grammar is not context free because of prototype instances... nevertheless if the XML pattern of ProtoInstance is adapted, a context-free grammar (CFG) for VRML is likely possible.
	
Round-trip testing will be quite possible using the X3D Example Archives as unit tests.

	X3D Resources, Example Scene Archives for X3D
	http://www.web3d.org/x3d/content/examples/X3dResources.html#Examples

Interesting possibilities!  Onward we go.
	
all the best, Don
-- 
Don Brutzman  Naval Postgraduate School, Code USW/Br       brutzman at nps.edu
Watkins 270,  MOVES Institute, Monterey CA 93943-5000 USA   +1.831.656.2149
X3D graphics, virtual worlds, navy robotics http://faculty.nps.edu/brutzman