Title: Message



If you 
define evolution as the accretion of new features, sure.  If you mean 
adding new 
instances of those features, no.  In any layered system, one must be 
careful to specify 
which 
layer is evolving vs one that is merely accreting.
 
If you 
define evolution as 'change' one *might* say this is evolution.  Amazon 
added categories 
so the 
addition of the categorical function is evolution (a new feature) but adding 
categories 
is 
extensibility.  
 
In a 
biological system, evolution is a feature that is inheritable.  Comparing 
that to Amazon, 
those 
are not evolution unless adding categories or search to Amazon adds it to any 

descendant of Amazon or any system derived from Amazon.   If 
Amazon cannot have 
decendants, it cannot evolve.   In this sense, evolution is an 
observable process of 
populations as they adapt to their environment, shape their environment, 
and then 
adapt 
to those changes (mediated feedback).    So my question to you 
is, what 
is the 
equivalent of Amazon.com genes?  Adding categories could mean the 

information is evolving, but Amazon evolved only when the categorical 
function 
was 
added, and then it accretes categories.
 
My position would be that XML evolution is in the addition or 
deletion of features 
of a 
schema (at any metalevel one cares to work) because it defines the system. 

 
So one 
might look at how instances acquire new elements and attributes that are 

then 
added to their schemas as definitions.  For example, 
aggregation:  why would 
one 
relax constraints such that composite documents become 
homogenous? 
One 
might do that if working on one product in isolation and fits HTML elements into 

say 
SVG applications.
 
Is XML 
an evolution of SGML or simply an adaptation (it lost features, so 

maybe 
it is devolution)?
 
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