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Re: [xml-dev] Why do W3C specifications have "implementation defined"parts?

If a specification defined everything it would be a product, not a 
This isn't facetious.   Its the real purpose of specifications.

Imagine a specification for a hex nut.
If you defined *everything* about including the materials, the exact 
dimensions (instead of the tolerences), the manufacturer,
the weight, the color , the hardness property of the materials etc.  
You'd be defining exactly 1 hex nut.

Specifications define a class of objects or processes not a specific 
one.  To define a class of things you by necessity need to leave some 
properties undefined so they can vary.   This is very useful.  The spec 
defines ideally the minimum set of properties that are useful for 
interoperability intentionally leaving a set of properties 
"implementation defined" so that innovation and deviation can occur in 
that set while still having usefulness.

Exactly where that line is drawn, and how and by whom, is another story 
... The line defines what the spec is or not.

David A. Lee

On 4/8/2010 8:06 AM, Costello, Roger L. wrote:
> Hi Folks,
> In many of the W3C specifications there are parts that are "implementation defined."
> To give one example, in the XSLT specification it says this about the<xsl:message>  element [1]:
>      The xsl:message instruction sends a message in an implementation-defined way.
>      The xsl:message instruction causes the creation of a new document, which is
>      typically serialized and output to an implementation-defined destination.
> 1. The purpose of a specification is to define a standard. Doesn't "implementation defined" defeat that purpose since it means that each vendor will define their implementation in their own way, thereby obviating standardization?
> 2.Is this unique to the W3C? Do other standards organizations also have "implementation defined" sections in their specifications?
> /Roger
> [1] http://www.w3.org/TR/2007/REC-xslt20-20070123/#message
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