Title: Message



That's 
good and I agree.  
 
On the 
other hand, if we use the biological definition for evolution, 

one 
could say that an XSLT program that makes a mistake when copying 

is 
evolving the input to an output form that may or may not be viable.  

This 
is similar to alleles.  If one construes copying to be a form of 

inheritance, then in the next generation as the mistake is copied into 

the 
next output, the trait is passed on.
 
The 
definition of evolution is messy in the scientific senses.  A quick google 

reveals the debate.  It's casual use seems to create 
controversy.
 
len

  
From: Alessandro Triglia 
  [mailto:sandro@m...]

  In my opinion, 
  if we refer to interfaces (or languages/syntaxes) rather than, generically, to 
  "information systems", the distinction between evolution and extension becomes 
  clearer and more useful.
   
  My 
  concept of "extensible" interface is that the interface supports certain 
  rigorously-defined extensions to it with the following 
  property:
   
  ------------------
  Given:
   
  - an implementation that exposes the base 
  (non-extended) interface B;
  - an implementation that exposes an extended 
  interface E1;
  
  - an implementation that exposes another 
  extended interface E2,
   
  a 
  program written to use interface B is guaranteed to work (as expected) when 
  using any of these three implementations, "thinking" that it is using an 
  implementation of interface B.
  ------------------
   
  The 
  same concept of extensibility would also apply to 
  languages/syntaxes.
   
  On 
  the other hand, if an interface or a language "evolves", one cannot expect 
  that the condition above is satisfied (although it could 
  be).
   
  In 
  other words, while I expect to be able to use an extended interface as if it 
  were the corresponding base interface, I don't expect to be able to use 
  an evolved interface as if it were the corresponding unevolved 
  interface.  Same thing for a language/syntax.
   
  I 
  think "evolvability" in this context means simply that an interface or a 
  language can be modified easily, inexpensively, and nicely, in order to 
  meet new requirements - without implying that a user can ignore that there has 
  been a modification.
   
  If 
  we refer to a system, I would say that it is possible for a system to 
  *evolve* while some of its interfaces are simply *extended* (while others 
  evolve).
   
  Alessandro Triglia
   
  
    
    -----Original Message-----
From: Bullard, 
    Claude L (Len) [mailto:len.bullard@i...] 
Sent: 
    Wednesday, June 02, 2004 09:23
To: 'Roger L. Costello'; 
    xml-dev@l...
Subject: RE: [xml-dev] [OT] Difference 
    between an extensible versus an evolvable information 
    system?


    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