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Re: what do "compositor" and "particle" mean?

  • From: Michael Kay <mike@saxonica.com>
  • To: xml-dev@lists.xml.org
  • Date: Wed, 08 Dec 2010 11:33:50 +0000

Re:  what do "compositor" and "particle" mean?
On 08/12/2010 05:52, Thufir wrote:
> What's the derivation of these words in relation to schema?  I don't
> really understand the definition nor distinction between the two.

Yes, it's terribly confusing.

Think of the grammar (the content model for a complex type) as a tree. 
Particles are the nodes on that tree. The terminal nodes are element 
particles and wildcard particles; the non-terminal nodes are model group 
particles. A compositor (all, choice, sequence) is a label or property 
appearing on a non-terminal node in the tree.

By analogy, think of the tree for an expression like (a + b*c). There 
are terminal (leaf) nodes representing the symbols a, b, c, and 
non-terminal (non-leaf) nodes representing the operators + and *. All 
the nodes are particles; the compositors correspond to the operators (+, 
*) appearing as labels on the non-leaf nodes. Now replace this 
expression with a grammar like (a | b c); hopefully the analogy becomes 

Michael Kay

>    At
> the moment, I'm referencing
> http://www.xml.com/pub/a/2000/11/29/schemas/part1.html?page=4
> for the most part as a tutorial.
> compositors:
> sequence
> choice
> all
> particles:
> element
> sequence
> choice
> but would welcome pointers to better material explaining this
> particular sub-topic in more detail as I haven't found a better source
> as of yet.
> thanks,
> Thufir
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