[vos-d] Mixing abstract/logical semantics and 3D graphics info

[Reed Hedges]

I think the main VOS approach to adding semantics like this is through 
the use of types on an object.  So an object may have type 
"a3dl:object3d.cylinder", and it may also have type "ai:tag.tree" or 
something. Types typically imply further semantics to expect from the 
object, such as properties or links to other objects.  Grouping and 
pointer objects can be used to seperate groups of children from other 
types so they don't try to use them.  Or types can just act as tags.

These multiple types live in parallel, as real equal citizens, so no one 
type has to be "subordinate" to another in a hierarchy (like a chain of 
child objects "object" -> "semantic thing" -> "tree" -> "object3d" -> 
"cylinder", and the semantic data is always an important and persistent 
member of the objects.  It's not just an alias or an extra string data 
field.

Types are also one of the options for selecting objects when you do a 
search query on a site.

I made this page to brainstorm "best way to design types and object 
structure": 
http://interreality.org/cgi-bin/moinwiki/moin.cgi/TipsAndBestPractices

Adding multiple types like this to objects is a pretty open ended tool, 
and there are potential pitfals or "doh, I wish I hadn't designed it 
like that" issues that we need to discover and document.

While hierarchy in 3D objects (i.e. a scene graph) is not yet 
implemented in TerAngreal, it will be. We need to tear it up a bit to do so.

Reed



Karsten Otto wrote:
> Am 25.01.2007 um 16:27 schrieb Len Bullard:
> 
>> X3D has a physics specification underway.   One is already being  
>> integrated
>> into Contact.  X3D already has shaders and scripting plus a  
>> metadata node
>> for indicating semantics.  Since the objects you mention below can  
>> be notatd
>> as say DEF Tree and referenced by that name, I'm not sure what you  
>> want for
>> semantics past that which won't create a badly layered design.
>>
>> Collada was designed as a transfer format for games.  It is  
>> compatible with
>> X3D.
>>
> 
> Ok, I see this is a difficult concept to get across when people are  
> used to scene graphs. Let me try to explain it another way. Yes, you  
> can group primitives via DEF into a complex shape, and even give it  
> some name that suggests to the human reader what is meant by this  
> group. The problem is that DEF in VRML is designed as a syntactic  
> tool, not as a signifier for complex objects. Remember that you could  
> as easily group part of a world for editing convenience.
> 
> world --> transform --> DEF tree = (transform1--> sphere, transform2  
> --> cylinder) --> meta: "tree"
> 
> and
> 
> world --> transform1 --> sphere --> meta: "treetop"
> world --> transform2 --> cylinder --> meta: "treetrunk"
> 
> will be both be percieved by a human as a tree, but for an agent both  
> cases are still gibberish. The label "tree" does not help either, it  
> could as well have been "Baum" or "Arbol"; these are words that  
> require understandig of a human language to process, and agents  
> generally are not capable of that. You need a controlled vocabulary,  
> semantic URI, or similar concept identifier that is machine  
> understandable.
> 
> Finally, meta nodes may help a bit, but for an agent to userstand the  
> scene it would first have to extract them all, pick the semantically  
> relevant parts of the scene graph, and correlate them somehow. In the  
> first case this is easier than in the second case; sadly 3D modelling  
> tools tend towards the second case, especially when naive users toy  
> with them.  After all, it "looks" great, right? Unfortunately its a  
> bad situation for an agent interested primarily in the meta information.
> 
> I think this boils down to intended use. If you want a scene looking  
> good to a human, use a scene graph. If you want a machine  
> understandable scene, use a description language. If you want *both*,  
> well... pick a focus, and either emphasize the scene with attached  
> meta nodes, or emphasize the semantic description and attach the  
> geometry. Scene emphasis is mainstream, I happen to prefer semantic  
> emphasis. Think outward and inner beauty :-)
> 
> Regards,
> Karsten Otto (kao)
> 
> 
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