Ok, but Roger is seeking to distinguish these terms and scientists 
are seeking to formulate or preserve a more precise meaning for 
evolution.  Again, if all evolution means is change, then these 
are indistinguishable.   If it means the accretion of features 
that are inheritable in a population, then it is a different 
meaning.

In the case of XML, the evolution is in the application languages. 
We can split hairs on XML 1.0 or 1.1, but the evolution there is 
in the systems.  The language devolved into a simpler state.  That's 
fine because that enabled it to propagate when the environment 
changed.  To really understand evolution, one must consider 
population and environment.  Otherwise, the terms are indistinguishable 
from complexity as a measure of fitness.

len


From: Rick Marshall [mailto:rjm@z...]
 
> Is XML an evolution of SGML or simply an adaptation (it lost features, so
> maybe it is devolution)?

depends doesn't it - was losing most of our furry/hairy covering 
evolution or devolution? sometimes evolution means losing things in a 
tradeoff for an overall better position. one of the great lessons of 
chess and warfare (although today warfare must progress without loss, 
but the debate continues). there is any number of birds that have lost 
the ability to fly in exchange for an advantage on the ground or in the 
water.

as a counter to the "more categories isn't evolution" you could also 
consider the giraffe - is the long neck evolutionary or not. 
topographically it's the same as other mammal necks, 7 bones, etc - it's 
just very long. evolution or extension ;) ?

i think they're both the same. one way or another the system is changing 
to be better in a given situation. it may lose features, gain features, 
or change them. it's different because for some reason it needs to be.

rick

>  
> len
>
>
>     *From:* Roger L. Costello [mailto:costello@m...]
>
>     Hi Folks,
>      
>     I am interested in hearing your thoughts on the differences
>     between an information system that is extensible versus an
>     information system that is evolvable.
>      
>     For example, suppose that Amazon.com gives users the ability to do
>     a keyword search.  Further, suppose that Amazon empowers its users
>     to create new keywords (and map the new keywords to information at
>     the Web site).  Is this support for new keywords an example of
>     extensibility or evolution?  By adding new keywords has
>     Amazon merely been extended, or has it evolved? 
>      
>     Let's take another example.  Suppose that Amazon gives users the
>     ability to search by book category (e.g., Fiction, Non-Fiction,
>     etc.)  Further, suppose that Amazon empowers its users to create
>     new categories (and map the categories to information at the Web
>     site).  Is this support for new categories an example of
>     extensibility or evolution?  By adding new categories has Amazon
>     merely been extended, or has it evolved?
>      
>     If adding new keywords and adding new categories are merely
>     examples of extension, then can you give an example
>     of evolution?   /Roger
>