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Barbara Liskov

The Inventor of Abstract Data Types (1939)

When, in 1961, Los Angeles-born Barbara Liskov decided to apply for the graduate Mathematics program at Princeton, she received a little postcard that was as blunt as it was brief: Barbara was a woman and Princeton did not accept female students. In retrospect, though, this gruff rejection might have been a blessing in disguise. Namely, disappointed by her own naivety, Barbara decided to look for a job instead. This brought her to the Mitre Corporation, having its initial focus on the U.S. Air Force SAGE-Project. It is here where she discovered her love for computers and programming.

At Mitre, Barbara quickly recognized that any software application is a complex structure of interlocking parts, being continuously modified by a large team of software engineers. She reckoned that any change in the code could have unintended effects on the other parts of the software, requiring programmers to essentially rewrite the entire program. To combat this inconvenience, Barbara designed ‘CLU’. Being the first language to support data abstraction, it is frequently referred to as the first ever object-oriented programming language. By structuring computer programs in discrete chunks, changes in the program would now be less likely to affect code outside the designated boundaries. Together with the design of Argus - a distributed programming language - Barbara’s residency at Mitre would contribute profoundly to languages like Ada, C++, Java and Python. In turn, those languages are widely used for the creation of software applications for - among others - personal computers and the Internet.

Perhaps the success at Mitre motivated her to go back to school. Stanford University had less problems with her gender and, in 1968, she became the first woman to receive a PhD from a U.S. Computer Science department. The career that followed would see even more major breakthroughs in fundamental areas, such as in operating and distributed systems as well as in programming methodology. Notable contributions are Thor, an object-oriented database system, and the Liskov substitution principle, a particular definition of subtyping that got named after her.

“It’s hard to imagine what today’s programming and distributed systems would be like without Barbara’s many seminal contributions”, is why colleague John Guttag wished to nominate Barbara for a Turing Award. The following year, in 2009, she became the second female recipient ever. And, as mundane as her hobbies might appear - gardening and reading mystery novels - as modest as Barbara has stayed. After going out to dinner with family to celebrate the award, her son noticed that she seemed relieved that the furor finally passed. Now, she could return to the research that had always been driving her. At the age of 80, she continues to do so at MIT, focusing on Byzantine fault tolerance and distributed computing.

Barbara Liskov


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