Thorsten Froehlich wrote:
> In article <41d6806b$1@news.povray.org> , Bernd Fuhrmann 
> <Sil### [at] gmxde>  wrote:
> 
> 
>>It isn't. XML is a general markup language made by humans and has
>>certainly it's flaws. But XML is the best general markup language I know
>>of. In fact you might ask any IT professional for the best general
>>markup language and most sane will tell you: "Use XML".
> 
> 
> No, only the marketing department will.  Just like marketing departments
> told everybody that Java is the best general programming language five years
> ago.  XML is nothing but a huge hype producing documents several times the
> size of a well-designed binary counterpart that can be just as "easy" to
> parse (that that XML is trivial to parse).  XML certainly has its
> applications, but they are limited, not universal.

There is a hype for XML, yes. XML is not universal, true. To give a 
simple example: XML will never be suited to save MPEG movies. It's just 
a matter of space and decoding speed. XML is not suited to contain 
executable files since they don't really interoperability. But POVRay 
files are rather small. Parsing speed does not matter that much. They 
contain highly structured data. So XML is suited to contain that data. 
XML is, however, a bit hard for newbies to write, I admit.

But who was desperately in need of some harddrive space and started to 
tweak his POVRay files? Who used shorter identifiers to save some drive 
space? Use of XML will result in files that have three or four times the 
size of normal POVRay files. So what?

Besides: There is a binary version of XML under development. If it might 
be used to contain binary data it will rock like hell, if used properly.

> Just compare the traditional VRML (POV-Ray-like) syntax version to the XML
> syntax version of X3D. It will give you a very good idea why XML is
> unsuitable for describing 3D data.  In fact, X3Ds XML representation is
> probably one of the best examples of pointless use of XML.  Just consider
> how lists of vectors are expressed in X3D XML syntax and you should really
> notice.  Of course, the problem with keeping them in strings is the result
> of an inherent limitation of XML expressing data only as complex, nested
> collections of strings.

XML is just a way to give a document (which does include programs 
aswell) structure that is easy to parse. It does not specify the 
structure itself. I'd make the structure almost equivalent to POVRay's 
structure. So there wouldn't be that much overhead to vectors, numbers 
and things. But one would have instantly have some powerful parser that 
are able to assemble scenes. You'd have to write such a parser in POVRay 
which is a hard task.

>> You cannot do
>>this at all with POVRay since you cannot access scene objects.
> 
> That is true, you cannot do this in POV-Ray currently, but it is not a
> limitation of the SDL (scene description language) but the parser design,
> which is 15 years old and fairly outdated (and the 4.0 rewrite will take
> care of this).

Interesting: So you suggest to keep the SDL while adding commands to 
access scene objects, right? But how can one access scene objects 
without some kind of object model? Example:

Assume you have some scene like this:

---
camera {location <10,20,10> look_at <0,0,0>}
light_source {<-140,200,300> rgb <1.0, 1.0, 1>*2}
sphere {<-2,0,0> 1 pigment {rgb <1,0,0>}}
sphere {<0,0,0> 1 pigment {rgb <0,1,0>}}
sphere {<2,0,0> 1 pigment {rgb <0,0,1>}}
---

So how would you write a transformation like "Replace all sphere by a 
certain mesh"? Suggest a syntax! Do you know any programming language 
what is able to access it's own objects that way?

Now for the 4.0 rewrite: What will it be like? I just googled a bit, but 
I couldn't find anything about it. How do you know that similar 
limitations like the ones described won't appear again? Is there any 
information about it available?

Regards,
Bernd Fuhrmann

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