Capabilities vs. Functionality

Folks,

 

I recommend that we leverage the world of requirements 
engineering here.  As many of you know, in the circle of requirements 
engineering, requirements are typically characterized in terms of functional 
requirements (what the system is suppose to do) and other than functional 
requirements (how well the system is suppose to do "it").  The latter is 
usually cited to as either "non-functional" requirements or "quality 
attribute" requirements.  These other than functional requirements really 
address required levels of service or qualities of service (QoS).

 

Many folks in this world suggest that functionality and 
capability are synonymous.  I've seen this used over and over again 
throughout the systems engineering world and in the literature.  We could 
simply adopt that perspective; however, I argue that capability 
corresponds to not only how a system (or, in our world, a SOA service ) meets 
BOTH the required functionality and quality attributes.  In other 
words, in our world, Capability is a description of not only what the 
service can do but how well it can do it, and Functionality is just a 
description of what the service can do, independent of how well it can do 
it.  In that sense, Functionality is really a subset of 
Capability.

 

I really think it's just that simple, but then I have a simple 
mind!

 

My two cents...

 

 - Jeff