Liskov on Liskov
Barbara Liskov talks about her groundbreaking work
in data abstraction and distributed computing.
BarBara liskoV, a
professor at the Mas-
sachusetts Institute of Technology
(MIT) and winner of the 2008 ACM A.M.
Turing Award, has worked throughout
her career to make software systems
more accessible, reliable, and secure.
We caught up with her recently to discuss a few of her most important accomplishments—and to find out what
she’s working on now.
Let’s talk about CLu, the
programming language you
developed in the 1970s to
handle abstract data types.
Before I came to MIT, I was working on
the VENUS system, and I got some ideas
about a different way of modularizing
programs around what I called multi-operation modules. When I came to
MIT, I started to think of that in terms
of data types. And then I decided the
best way to continue the research was
to develop a programming language.
how did your ideas differ
from the research that was
going on at the time?
When I started, the main way people
thought about modularization was
in terms of subroutines—of abstracting from how you wrote a procedure
to calling that procedure, say, a sort
routine, or a lookup routine. But they
didn’t have any way of linking a bunch
of procedures together.
And that’s what CLu’s
Yes. A cluster would have all the operations you needed to interact with
a data object, and inside you could
implement it and later re-implement
it however you wanted.
programming evolved from
your work on CLu.
Object-oriented programming evolved
from two different strands. There was
my work on data abstraction and some
related work that was going on at [Carn-egie Mellon University]. The other influence was Smalltalk. Both of these were
sort of getting at the same idea in slightly different ways, but the big difference
between my work and the Smalltalk
work was that I focused on making a
very strong distinction between what
a module did [Continued on p. 119]
PhO TOGRAPh BY JARED LEEDS