Why is it important to distinguish between an extensible versus evolvable information system?

["Roger L. Costello" <costello@mitre.org>]

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