TI Composing Systems Using Tool Abstraction 

LT CUCS-034-90 

OR COLUM 

YR 1990 

AU David Garlan 

AU Gail E. Kaiser 

AU David Notkin 

AV ftp cs.columbia.edu:pubreportsreports-1990cucs-034?-90.ps.Z 

AB The well-known notion of data abstraction, which separates the
interface of a module from its implementation, permits the
representation and implementation of abstract data types to
evolve without affecting the module's clients.  However, many
enhancements change the function of a system, not just its
implementation.  Data abstraction does not directly ease the
difficulties and costs of such enhancements.  {\it Tool
abstraction} complements data abstraction by supporting
evolutionary changes that are made incrementally and
independently.  This approach structures a system as a pool of
shared data structures, viewed by a collection of cooperating
tools, each of which provides a piece of the overall function. 
This article identifies tool abstraction as the common foundation
of a variety of existing systems -- including spreadsheets,
structure-oriented environments, production systems, and
object-oriented systems.