Title: Message



Hi 
Folks,
 
Again, many thanks 
for all the excellent responses.
 
Kremena Gotcheva asked a particularly pertinent 
question: "Why do I ask [about the distinction between extensible versus 
evolvable]?"
 
There has been a lot of excellent 
discussion on what the terms "extensible" and "evolvable" mean.  I do 
not think that it is important to get hung up on the terms.  I would like 
to choose a definition and move 
forward.
 
The central issue, I believe, is this: "does an 
information system provide support for accessing and using information in ways 
that were never anticipated by the system designers?"  To my mind, a system 
which can dynamically change to meet new "information access paths" is an 
evolvable system.  This is the kind of system that I 
want.
 
Let me contrast the 
differences:
 
Extensible 
System
 
System A provides support for keyword searches.  
It also provides support for users to add a new keyword (and map the new keyword 
to the system's information).  It doesn't really matter what we call it, 
but just for discussion purposes I will call a system that supports 
the ability of users to add new keywords to an existing keyword search 
capability an "extensible system".
 
The ability of users to add new keywords to an 
existing, system-designed keyword search capability is a good and useful 
feature of the system.  But it is not the dynamic, adaptative, 
evolving capability that I am seeking to 
identify.
 
Evolvable 
System
 
System B does not provide support for keyword 
searches.  The system is primitive.  It just provides information (the 
building blocks) and mechanisms to connect/aggregate the information (mechanims 
for snapping the building blocks together).  

 
One mechanism that system B provides is the 
"related to" mechanism.  With this mechanism users build a keyword search 
capability.  Thus, through user interactions the system has changed - 
it now has support for keyword searches.  Further, the users may use the 
"related to" mechanism to create other search capabilities, such as category 
searches.  Thus, with basic building blocks rich, complex search 
capabilities are created.  
 
Again, it doesn't really matter what we call it, 
but just for discussion purposes I will call a system that supports 
the ability of users to create totally new search 
capabilities an "evolvable 
system".
 
The ability of a system to 
dynamically adapt and evolve to support capabilities that were never imagined by 
the system designers ... ah, now that's what I want out of a 
system!
 
So, why do I ask [about the distinction 
between extensible versus evolvable]?  Answer: I want us to (colllectively) 
identify the fundamental differences and characteristics of an extensible system 
versus an evolvable system.  
 
Comments?  
/Roger