The HLF Portraits: Barbara Liskov

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The HLF Portraits: Barbara Liskov
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2017
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The Heidelberg Laureate Forum Foundation presents the HLF Portraits: Barbara Liskov; ACM A.M. Turing Award, 2008 Recipients of the ACM A.M. Turing Award and the Abel Prize in discussion with Marc Pachter, Director Emeritus National Portrait Gallery, Smithsonian Institute, about their lives, their research, their careers and the circumstances that led to the awards. Video interviews produced for the Heidelberg Laureate Forum Foundation by the Berlin photographer Peter Badge. The opinions expressed in this video do not necessarily reflect the views of the Heidelberg Laureate Forum Foundation or any other person or associated institution involved in the making and distribution of the video. Background: The Heidelberg Laureate Forum Foundation (HLFF) annually organizes the Heidelberg Laureate Forum (HLF), which is a networking event for mathematicians and computer scientists from all over the world. The HLFF was established and is funded by the German foundation the Klaus Tschira Stiftung (KTS), which promotes natural sciences, mathematics and computer science. The HLF is strongly supported by the award-granting institutions, the Association for Computing Machinery (ACM: ACM A.M. Turing Award, ACM Prize in Computing), the International Mathematical Union (IMU: Fields Medal, Nevanlinna Prize), and the Norwegian Academy of Science and Letters (DNVA: Abel Prize). The Scientific Partners of the HLFF are the Heidelberg Institute for Theoretical Studies (HITS) and Heidelberg University.

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[Music] to begin at the beginning where are you as a child I'm going to say 8 you're 8 where are you what is your family life like I'm living in San Francisco that's where I grew up I have a younger sister my father is a lawyer my mother is a housewife and I'm going to elementary school public school public school in the city itself in the city yeah in the city let's also take a little bit what are your parents expectations for you they're definitely expecting me to go to college they're definitely expecting me to do well in school my father's attitude was that it always had to be all A's okay yep not important there's no sense that the voice of the family might go one direction of the girl the other you you are you you're not to this the highest and there were no boys world yes I think that mattered my brother is nine years younger than me and but at you know as I when I was really small there were no boys have you were the eldest obviously all this was not really firstborn Yeah right so really the expectations are high yes yeah although I don't think there was we never talked about careers it was just you know it was just you know do well right now it might be significant turned out that your mother is a homemaker I'm he did had she got university everything we can't she was a graduate of UC Berkeley okay and she graduated in when it was the depression she worked for a bit as a in a day care center and then she decided her father her father was a pharmacist and pharmacists were not badly hit the depression so she gave up her job because there were much easier people who needed it so she was just at home if she was a very bright woman yes and in retrospect I think that it mattered a lot that she never interfered with what I was doing I think sometimes girls get kind of a negative message from their mothers oh you did not I did I didn't get anything about you should do this or that I got you know just support other books oh yeah lots of I read all the time you know we went to the library every week I would get out you know as many books as they would let me my mother used to insist that I stop reading and go outside and play it she was kind of please a little bit you read do you know she wasn't a person who necessarily led on to that kind of stuff she just felt it was good to get freshen up okay in California that's particularly easy so I want to decide with you when we begin to see the glimmer of the scientist is anything science particularly attracting you it was more math I think it was more math I was just I just liked it and I can remember at that age or younger you know memorizing the multiplication table was just something you know that and I don't think that anybody was telling me to do stuff like this I think it was just it was interesting I found I found it easy to put you to school really either elementary or beyond what kind of education California had a pretty good system at that time it had a good system I think still there are some good public schools there you it was okay I when I was ten or nine we moved and then we were in a better we were in a working-class neighborhood when I was little and then we moved to a more affluent neighborhood as still in the city I think that second school was better okay although by then I was getting close to the end of it so that was elementary school um because of the limitation of to put you in high school okay what is the curriculum like are there Mentors potentially there is anyone sensing your abilities I sure don't remember anything like that what the only thing I remember like that was thinning I was in the fourth grade I guess I was so far ahead of the kids in math that my teacher asked me to start helping teach the other kids really in the fourth grade but that's the only thing I can remember like this one of the dilemmas very often for women are for minorities and all of those who were not inevitably headed particularly for a scientific career of Africa where is high school counseling which is suggesting a rather limited range or options are you getting counseling in any direction the funniest part of it was I would say that whatever they were telling me I wasn't paying any attention to I was just taking the most advanced courses and I took all the math and science courses that were offered oh and I don't recall anybody saying I should do this I mean it's probably in line with what my father thought but I also think it was interest and I felt at the time that it wasn't it wasn't something my peers thought I should be doing so I kind of did it quietly quietly but still what can argue perversely I mean that's fine whatever the broader message in spite of that message you're doing it I was doing it what are you doing but the funny story is that probably when we were juniors in high school they had everybody take a an exam that was supposed to help you figure out what your career should be and they came back and told me I should be a landscape architect and this I think it was because I mean they would never have suggested I become a scientist or math whatever size so they this was you know some combination of some scientific skills and the fact that I was very interested in the outdoors so humanists use of your talents yeah something like that okay well it was different in those days or at least where I grew up you know there was the wonderful UC system it was free and the only thing was that you know Berkeley was better than the rest of them so but you could get into Berkeley if your GPA was at a certain level so it was no problem no problem yeah I'm guessing your GPA was a yes it was it was really different than the percentage of kids going into college prep was pretty small and you know nowadays I think that competition is huge right I think it was as bad so it was a smooth next step you're probably had expected you to go to university in any case yes it wasn't so expensive that's where my mother went right I mean your mother yes so there you are I guess you don't have to decide on a major your first year but how are you picking courses and thinking about it so I went in thinking I would be a physics major physics yes Berkeley by the way has a separate engineering school and you apply to it separately and I do nothing about that and if I had realized I wouldn't have done it because I really did not see myself as an engineer right anyway what I think physics was because it was the hardest major but before long I realized that I was really better in math I like math better so I switch to mathematics you're not the only one of the laureates of those categories that started with physics and then switch switch to math or others so how long do we keep you the physics before this as you said we don't have to choose at Berkeley right so I had probably already decided this early in the second year or something like that the courses were the same it really came down to what did I do after the first two years because it the way it worked then there were certain physics courses you took I took all of those and then when you got to be a junior you've never been a major in physics the more advanced courses were to go on in one direction and math one in another direction so are you noticing that you're doing pretty well in these courses especially the math especially than that yeah yeah but I'm not really thinking about it there were very few girls in these classes yes and were there others at home in some there were none and some there might have been one
I was keeping a pretty low profile mm-hmm and you know I was the first or the second in the class with this being remark Tom or you're there so you're there nobody's paying much attention okay so it was really just more a decision about what courses I'm going to take next year I decided to do the math so instead within the context formerly of a physics major well yeah I don't even remember when you declare a major okay so but I think that by the time you would have started to make the decisions that actually mattered so the first two years I was prepared to major in either one and I went off and I just took much more many more courses in their area at this comparatively early Saints although in math was abilities come earlier yeah but are you finding a particular direction in math that's fascinating you or you're just hungrily I'm just taking I'm just consuming I think I had realized I like discrete math better than continuous divided for me the difference between discrete well things like set theory linear algebra as opposed to calculus differential equations and you know now I can see that's a lot more like computer science but then you're just following here yeah your interest yes yeah you graduated with probably some distinction I can't remember I graduated I actually applied to grad school in math and I was admitted at Berkeley but I decided that I wouldn't go on right then because I wasn't dedicated well no you know I've done some background work I think because you applied to Princeton when Kristin was admitting women didn't this is inconceivable now that I want to yeah did they announce this did nobody advise you not to apply were you aware of this restriction not not until I got a postcard back from them were they statement yes they did not accept women yes in math yes I didn't keep this postcard so you know what memories are not that reliable so this is my memory of it yes yeah yeah that would belong to museum yeah I was surprised I mean Princeton at that time did not have under women undergraduates so I knew I couldn't have gone there as an undergraduate I thought at the graduate level it would be different what is the year now because I know that in the 50s Harvard med actually had female faculty but women could not I be admitted as as students I mean is a very bizarre time for this this is undergraduates you're talking about graduate students okay so it was yeah yeah not unlike your situation so it's curious they have distinguished faculty yeah but women were not allowed in the medicine I have talked to people who were undergraduates at Radcliffe and I think it was good that I didn't go there because they have stories about how they could take the courses with the men but they had to take their exams separately and they couldn't go to the library at this and that really seems like yeah century to go but it's not all right so you early but you but you decide like I felt I wasn't dedicated enough I didn't really want to go on to that next level okay and I think under the covers though I didn't really bring this out I realized I wasn't as good as I needed to be because you know math is a very there are people who are just obviously going to be the math geniuses and if you're not quite at that level even if you're very good you're not going to get there and I think I knew this although I didn't articulate it I thought of it more as you know to go to graduate school you'd have better really commit yourself and I wasn't ready to do that but you want to begin a career somehow relate is your education I wanted to use my education to get a job that paid a decent wage fair enough so where do you want it well I decided to go to Boston because my father grew up in this area and I'd never experienced it and I had a friend who graduated from Stanford who was interested in doing this so we decided to do it together oh and she had majored in biology and she got a job as a research assistant in a lab at Harvard and I came here without a job and I stayed with my aunt and started applying for jobs my aunt told me that I would never get a job at it you know I'd only be able to get a job as a secretary and you know the wages would be very low and so forth anyway I was applying for a job based on my math and I did have lots of spite a few job interviews and the jobs that were offered me were not interesting they were you know plot graphs very low-level master really is not surprising given you know what math is really like but I got a job offer as a programmer from The MITRE corporation that sounded a lot more interesting yes and tell me a little bit about what the job is like actually the job was actually very funny in retrospect well first of all the computer science was really new then yes and there weren't people coming out with undergraduate degree so they were hiring anybody they thought might be able to do it and so they were taking a chance on me just like they took a chance on a lot of other people many of whom were women yes not all of whom were in math some of them were in English or something like you know either you can think this way or you can't write and so it's sort of walls you know works itself out again I'm guessing you're doing pretty well at this just so they handed me they handed me on my first day of Fortran manual and they said write a program to do this so I'm entirely self-taught but yes I was really good at and I realized you know it was what I really liked so it's his solutions of the math dilemma yeah in a way deciding the best outlet for your intellectual yes yeah I think you're their ally here I I decided after a year that I was living in Cambridge and wouldn't it be nice I saw an ad at Harvard in the Harvard computation lab they were looking for programmers I thought well that'd be much more convenient hmm so I convenient yes make the difference than the jobs you know it wasn't that the job was better was easier to get much easier to get to and they actually offered me a higher salary in the first settlement confounded my aunt's expectations at the second one and at that point mitre tried to you know keep me but since I was matter of I really prefer to work in Cambridge there was no way that was going to happen fair enough so what are the tests that you are assigned in Harvard Harvard turned out to be a really good change because at mitre had been working in Fortran so I'd learned how to use a higher-level language and mitre I was maintaining their huge machine program program written in assembler so then I began to see what the underpinnings of a computer program are like what the compiler does and what really happens when the hardware runs I also got to see what a really big program looked like and I think it probably was the beginning of a lot of the stuff I did later where I was thinking about how to structure large software systems so the convenient the move of convenience turned out to be a determinant in your intellectual development it did because it really broadened what I had learned at mitre in this new direction so how do we get you to graduate school finally well it must have been in that fall because you have to apply in the fall early yeah that I decided that I was learning really fast but it was all self-taught and I might learn a lot faster if I went back to school plus I think I was ready to go back to California because I've been with for two years right of course so I applied to Stanford and Harvard I didn't apply to MIT because I thought I've been mighty as a an engineering school where I wouldn't want to be and in which schools did you apply just Harvard and Stanford no but I mean universities I mean which direction what well cool of what so so Stanford
had a program in computer science it was a sort of combination between engineering and math and so I applied to that and I applied to Harvard I don't remember but you know since I was working there it would have been in what they call applied math okay this is obviously the beginning days of the capacity and choose the computer career so this is the way each University is shaping its the element developing program so Stanford accepted you and perhaps it's romantic to say but that must have been an extremely exciting or to whine of it Stanford I guess I don't know I remember that it fit what what I wanted to do which was to move back to California you know I wasn't getting guidance and I didn't understand that Stanford is one of the three places in the country that you really wanted to check out I just know that unfortunate yes which actually affected both what you did invite here at Harvard - yes there's some my portrait look yeah but there's also your response to the law that's right I think that everybody has stories like this so there we were at Stanford you don't know that you're the place that is beginning so many things you're expecting a PhD if you finish the course in what what would that computer science it would be called computer science well you know again this is a sort of a formal definition that I you know think about right but I was in a program that was really computer science and so whatever they called it it would have been computer science as it turned out they turned into a department a couple of years after I was there yeah I think there's a professor who influences your time they're not McCarthy yes was my advisor he was a Turing Award winner and my recollection is that I I went to Stanford without any financial support I wasn't really worried about this because I had been saving all the money I'd made and I just didn't think about it but I my recollection is that I met him walking up the steps on the first day at Stanford and I asked him if he would support me and he said yes now it's highly unlikely that this is you know the whole story or yeah my guess is they admitted me because of I've been working on it at Harvard in the quote language translation project and so they thought of me as being an artificial intelligence person even though I was just a programmer and so maybe they had already thought I might end up working with McCarthy he had a lot of research money so he was looking for students but it was kind of happenstance maybe you know if I've met somebody else on the first day I might agree right but having sex is important so there you are you're in his lab essentially yes what are the kinds of problems that you're addressing it to what he said will it affect your dissertation now that's a problem I have trouble answering Stanford does not have a master's thesis even now and didn't have it then so there was no notion of a of a first project that you completed and wrote up we have that at MIT I think it's actually helpful because it can be small and it gets you sort of started so I was mostly you know I don't know really very nice but you're you have tests oh I'm definitely I'm a I'm working on classes I seem to have been writing little papers about this and that I don't know why you know in retrospect clearly that was a little unusual but it didn't seem unusual to me at one time Nikolas veered who was also on the faculty at that point he's another Turing Award winner who is in programming languages tried to get me to switch over to programming languages because I was interested in you know things that were going on in compiler constructions later I've you will be very interested in these kinds of yeah I never really went into the pilots but programming languages for sure but I decided that was probably third year maybe and just seemed better to stick in AI because I probably could get done finish finish sooner yeah good a good kind of decision for a career are you looking at rather than seeing any other women there's just a woman that following year this is Sucre who became a professor at UC Berkeley there was another woman in that class in my class there was AI was just me but it was very small maybe there were certainly no more than ten some small number of students they never had a kind of a class organization where you said oh here's your class but it was really small and Raj Reddy who was another attorney award-winning he was a we actually worked we didn't work together but we both worked for McCarthy so we knew each other quite well right and anyway so I was the only girl in my class in the next year when sue came there was a second girl who ended up not staying and so there were you know one or two one or two yeah in the broader question of collegiality among graduate students is there a lot of interchange going on or you know they were very collegial and we used to take classes and we get together in the computer room at night run our programs I never sensed any sort of I would say someone was much more collegial than anything I ever experienced yet when I was a math major at Berkeley MA so you are is there a sense of the excitement about an emerging field that everybody
is the ground I have a lot more people just well I would say that definitely the professors probably sense this I think the students are more I mean they chose the career for a reason but I don't think we understood what it meant I certainly didn't understand what it meant to have lucked out and gotten into a field that was just a virgin yeah what is your dissertation topic it was a program to play chess in games describe what it was what the inquiry was the inquiry was whether well to give you a background user you need to understand that computers were not very powerful in those days they were slow and churches the chess is basically a search game so you start with a particular position on the board and you ask the question if I make this move you know what will the counter moves yes you're thinking about what's the in position and today the computers can search very deeply then they could hardly search at all oh so in order in any way still you have to prune the search cuz it just gets gigantic but then used to prune it very aggressively so then the question was well what's the most effective way to prune it so that you don't throw away the good paths but you don't keep the ones that are worth pursuing and so John McCarthy had a hypothesis that for the end games you could use this notion of better and worse so you had a way of analyzing a position that would tell you whether it was better than where you are and maybe better than some other choices that you had to make and so he wanted to see whether that wasn't effective and he thought I would be a good person to work on that because I didn't play chess and therefore I could go read the books and I could see which I think maybe this was correct I could see in them the ways they were expressing they were explaining people what heuristics they might think about using it I've been thinking about it more as a program than like something I'm really familiar with so I worked it out for a few in games it worked for those in games I never thought it was really very important but it was again a means to an end by then I'd already decided I didn't want to be an AI had already decided that yeah that was also along the lines of you know I would have probably preferred to have worked with fear but yes I decided it was better to get done yeah this is a practical streak in you apparently who you know much is not made of the fact that you're one of the few women first certainly where they have to get a PhD in computer sciences again I keep asking this and probably the truth is it wasn't this big a deal then but tell me was much made of this no I didn't think about it at all you know I was just one of the students and I think Raj got the first degree and I got the second one and or maybe bill McKee me about the first one I mean that we're really we were really early but I wasn't thinking about it from that perspective at all good yeah I'm just doing my thing right okay now again at the cusp of a post PhD career very often certainly later
but maybe at this point or not there's the question of do I go at academia do I do industry how are you thinking about that that's that I was thinking about academia like again didn't have any guidance I didn't even know to ask for guidance and thought I was looking around like I did apply to some places and the only academic job position that I got was at I can't remember which one it was it was some state school in California on the other side of the bay like Milpitas or sometimes like that and I knew that wouldn't be a good decision earlier well from an academic I said you know it'd have been good teaching but research was nothing and I could have stayed and worked at SSRI and you know that would have been a good research position but I had met my husband by then and I wanted to go back to the Boston area you met him within said that's that man and while I was a student when you were sued that he wasn't no he was out on business okay and so I applied to MIT and they offered me a research position okay and and I tried to miter and might have offered me and if I T it would have been a I was applying as a faculty member so the fact that they weren't willing to give me a faculty position meant it was some sort of second class thing yeah I mean if I hadn't been a woman maybe they wouldn't wouldn't benefit but I think actually there was an old boys network at work I didn't know that and so they were in hiring the students of their friends and these would always be young males at that stage yeah okay well miner doesn't have this problem either well my guru me you know my guru me so they were they were interested to hire me and that was a real research position it was in systems which is what I wanted to switch to or it could be whatever I want and then they come to us and decide what you want to do now they have you know their various projects they're working on the way it works at mitre when you're a young researcher is they have various things like funding for various projects they've lined up and they give you something so they gave you something you're very interested at the task at hand Gary this is soon in here this is fascinating and I think of it now and I somebody asked me and one of these I don't know someone I was talking you know didn't you find it kind of scary that they had asked you to do this stuff which really wasn't like anything you'd looked at before and no I didn't I found it fascinating it was like about a box of candy they presented me with and they and they gave me complete freedom idea just charger lovely decent salary oh yeah for those days so I think it's at this context that you create with the Scioscia survey the entirely idea of the Venus computer yes the first part of the project I did with an associate his name was Bob Curtis he didn't have a PhD s very bright man and we did work together on that then the second part I did entirely on my own that was the hit the software part that worked on top of the hardware can you describe what it was doing it was a project to invest something called micro programming microprogramming was in Venice by Moore's Wilkes who was one of the early Turing Award winners and the idea was to have an intermediate language below above the hardware but below the instruction set that people use so you would you would design the instruction set interpreted in terms of this low-level stuff right and then it would run on the hardware and this made the hard with the job of designing the hardware easier because they had a simpler interface to design to and so I was working with a particular piece of hardware the inner data for I think and my job was to invent an instruction set and implement it using micro programming the microprogram went into a read-only memory very small and then you could run anything people wrote in this instruction set and would have interpreted using the hardware instructions so the first job was to design that instruction set and you couldn't do very many instructions but a lot more than what you had available at the hardware level and one of the things that was interesting was we decided to put semaphores into the hardware and that was an idea that came from diced or another Turing Award winner one of the you know one of the things that's been wonderfully my careers I got to know all these people yes my gorilla corporation profit motive it's a non-profit it works for the government I see and it does it still works more or less in the same mode it did then they the government puts out requests for proposals minor bids on them they have certain specialties oddly enough my son works for Leiter oh and he's a computer scientist but he's more on he's in security so then nobody is worried about monetizing anything you do oh I think people oh no they weren't worried about monetizing it was more the government wanting to know is this a viable thing to do okay it was really research how long are you in later I was there for years because after the Venus Project then I went on to do the program methodology stuff which was really the start of you know the ideas that went to the Turing award so I mean this is the way mitre worked then and I think to some extent mr. works now I was finishing up the Venus Project and they asked me to look at this problem of the software crisis so this was another place where somebody had bid on a proposal from the government and so then they were looking for somebody to do the research and so I start to look into this and the software crisis had to do with the fact that they didn't know how to build software and the programs they were building were not working correctly we have to sometimes in the end in the entire project and even though it was early day some of these were pretty complicated program don't ballistic missile guidance install right now and so my job was to start to look into this is probably in substance much less directed word search than the first project was there it was you know find that instruction set then showed that that instruction set is useful but here it's more here's a huge problem see what you can make of it for intellectual developers they're much more like being a professor more like what do you make of it was fascinating I mean I read all the papers nobody had any answers you know there were some people that had suggestions here and there right and and so I was thinking about it and along the way I realized that in designing the software for the Venus operating system I had actually put a programming methodology in place and not because I was thinking about programming methodology but because I was worried about how are we going to manage the complexity of the software so I was already in some sense thinking about the topic and program methodology without realizing it right you know yes well maybe that's always true also really anyway so I wrote that up and in the meantime I had written a paper on venus and submitted it to s OSP the systems conference and it was accepted and it was an award paper and when i went out there and this would be in the fall of
1970 it could have been this it was probably the fall of 1971 right and so corby professor corbett o otherwise return award winner was in the audience and Jerry Saltz er a professor at MIT was the head of my session and they were then actively for women so and so and they're probably where they're probably Jack Davis was there too so there was a group of people from MIT and me and again I'm very naive so I don't really know what's going on but as a result of this I was invited to apply to MIT which is not a bad no and I was actually invited to play to Berkeley to really and I didn't even Bob I didn't go because I told them there was no way I was gonna move back to California because my husband's job you know wasn't available yeah at least for that short works has originated and here it is you know almost 50 years later yes so so I had to apply you have to leave a talk you know honestly it must have been on Venus but I don't remember what it was about uh-huh I remember a little bit of the interview process you don't seem like a nervous person so you're not at this point in my guessing so racked about oh my god will I do well will they take me or not you know I don't know I don't remember I had a good job yes you don't actually lead this I didn't need that but it was something I was interested in yes so I it was just exploited to see what would happen right but when they offered me the job I took an instant because there was definitely you know it had been what I thought I would want to do another thing that happened while I was at mitre was I changed my expectation about what my life was going to be like because I had thought that and this was not uncommon for women at that time that I would work until you know I had children right there used to be you would work till you got married in the made once you believe you know so now you had a few four years yeah say nothing till you have children and I used to think about you know this was something I was doing and then after that I would do something else but I realized when I was at mitre that this was not true that I really wanted to do this stuff and I wouldn't stop very important you're an MIT you what is your right assistant professor your assistant professor and what are you either TAS to do or what do you choose to have to do with this new leverage well so there's the task in the choosing okay the task is teaching yes and MIT is to this day very strong teaching school and all faculty were expected to teach the faculty load is one course a semester and there wasn't actually a computer science department there there wasn't even electrical engineering in computer science I was hired and EE really and the course they gave me to teach was of course about computer architecture these are team taught so I was teaching a recitation and it involved quite a bit of hardware which I knew nothing about them so that was a real scramble and not only that but I don't think the students were very happy to see a woman they were definitely students in the class who were trying to test me and given that I was you know two weeks ahead of them maybe got two weeks ahead of those I had to learn how to manage that right so that was a heart that was a hard first semester right fortunately I did teach that course several times because once you do it once you you know it's much easier to do it the second time and you did survive of that and I did learn how to manage my students and you know yes but I the interesting case I got this from the students I didn't get this from my colleagues and but then on the other side I have to find my research and the research was was the way it works in in the electrical engineering department the ECS is they have these labs and the labs kind of cut it's like a matrix organization kind of a departmental structure and so I was in the lab for computer science and no actually there was just project Mac in those days because LCS didn't exist yet and they had sited that I should be in a yacht so they stuck me right they stuck me up on the AI floor and they even asked me to go work with somebody or other and I wasn't having any of that but that was pretty miserable so I had to figure out how to sort of get out of this dilemma meanwhile I'm thinking about programming methodology because that's what I really want to work on right so in a way I had no trouble with the second part I already knew the research I wanted to do but I had to kind of manipulate this and Jack Dennis who was a professor there was very helpful to me he was really a mentor and he helped me move my office to a different floor and you know sort of encouraged me to look to get into the research I was doing so he was helpful and you got it right I mean in terms of your interests yes then it was the right place to be and he was very interested in the work I was doing and you know so that was very helpful is it the clu programming that yeah the first year was actually writing the paper on data abstraction which was the basis for clue and all the stuff that happened after that and then starting in the second year it was design and clue and Jack used to come to those design meetings and I mean in the end you know he didn't we didn't really work together but he was just really good at you know feeling making me feel supportive it's a little bit of luck this usual yeah relationship what are the objectives what are you setting out to achieve or what is the problem at hand so the problem is this very abstract problem of how do you organize software so that in the end you can control the complexity and make sense out of it okay and the solution is modularity so you have to break the software up into modules that where they have a interface that describes what they do and then inside might be a really complicated implementation which might make use of other modules so it's a higher oh and use ideas like this and lots of area certainly in engineering sometimes the modularity comes out of physical constraints here though it's entirely intellectual it's the only only by having these simple independent blocks that you can reason about independently can you really keep control of stuff and that was what people were struggling to come up with at that time this kind of stuff was not understood and data abstraction is a new kind of modularity so and it was a huge step forward to come up with that idea the only modules they had before that were procedures like you know how to sort that could be something separate from all the rest of us the program was doing and data abstractions do more because they have it's like a file system as a data abstraction there's many operations on file so it's a huge amount of complexity down below to get it all implemented so that kind of thing there was although I don't remember it specifically but there was a moment when all of a sudden I saw that there was such a thing as data abstraction uh-huh and prior to that I had been working just with I mean I've just been thinking about this all these papers my own ideas about from their methodology and trying to find a way that would make these useful and program said they didn't remain so abstract right and what I thought of data abstraction I realized that this was something to put into a programming language this is something programmers would understand because they already understood about procedures so abstracting from how do you do something to accomplish a particular task was already something in their repertoire was just this was a different kind of task so you know yes I knew when I thought of that that this was a really good idea terrific again because it's such a rich career in such a limited time I'm gonna
jump into the process of creating the Argos language okay so I worked on clue for most of the 70s and with a group of students you know of course you don't ever work along when you're in an academic career and when it got finished around about 1978 I was looking around for what to do next and one thing I was thinking about was continuing the work on clue and maybe but I thought I it would just be pretty incremental to keep working in programming languages at that point and then I discovered a paper Bob Khans who's another internet give me a Turing Award winner and I discovered the internet which I had not been paying attention to of I had been using email already for several years right and I discovered in reading his paper by Bob that there was a kind of a dream of writing distributed programs where there were components on different computers connected by a network but people didn't really know how to do that yeah so I thought here's a great research project so it was it was it was it switched me so I Argos was the first part of that project I designed a programming language how do you organize that task with colleagues and so forth you say this is my next interest do you then find just the process of creating a team so I always had students who wanted to work with me you'd have to get money but money was easy to come by in those days because we got a big block grant from DARPA and all I had to do was write a couple of pages and of course DARPA was where this came from in the first place so they were very interested in this right I don't think bob was there anymore at that point but I can't really remember so anyway you know so I had money and I had students in my group who were looking for things to do and it was a programming language project so you know we started working on a programming language I didn't do much of anything except you know so to keep on going and explaining new ideas to people and I used to write I would write NSF proposals also there they don't bring in the kind of money that the darker grants do but they you do explain your ideas and so they're good for that right I supported the explanation is subsets or guests at the implications of other work that's right so why is it important to do it is how are you going to know about it so I wrote something but I don't remember what I wrote right at what point do you see success in this enterprise I mean what so well we had a goal we were going to design and implement Argos and get it running on multiple computers right and I had a group of you know students working with me on that and I even had a staff member you know so by then there's also a lot of programming involved and right and I had to give up programming because there's a limited amount of time you have these very time-consuming yeah so I was doing less and less programming yeah enough ask for somebody to word I would describe you know what needs to be done and I would certainly be involved in design details but the actual writing and debugging of the code yes yes and you somehow I got together enough equipment so we could do these experiments but that again was not difficult at that time because there were we had a lot of money yeah yeah you know it wasn't Nestle it was either Golden Age in terms of yeah I did say problems like is there always interesting problems but but support and maybe even acceleration of insight it certainly was a very good time to be doing research right right yeah I know that there's such things that Liskov substitution principle but I don't understand okay so that was later okay what happened with Argos though was that it sort of pushed me into distributed systems which has been a major focus of my work ever since then and I went off in many different directions based on that that was just another interesting field the Liskov substitution principle which has turned out to be extremely influential came about not because I have a research project looking into this it was because I was asked to give a talk at the oops law about the object oriented programming I forgot what the acronym means but anyways the main object-oriented conference I think it might have been the second keynote so it's the second year they ran the conference and so I said okay and I at that point I decided well I probably better find out what's going on an object over are going to program me so I was I was doing the data abstraction part and then in California Allen case group another attorney and and other people in Silicon Valley were interested in what's called object oriented this notion of their objects and their hierarchical you can implement a new kind of object by taking the code of an old kind of object and just adding to it and changing it a little bit and that those ideas came from Simula 67 which Oh Leo Honda and Kristin Nyberg so they were working away on object-oriented programming and I was working on data abstraction where the focus was much more on encapsulation modules that were that had hidden implementations on the inside and the outside was described by a specification and I was interested in how do you prove the correctness of the code and how do you reason about stuff and so I hadn't been reading the literature that was more the object-oriented literature and I decided to read some of it and I discovered that they didn't really have this strict notion of modularity they had more of an idea of just developing code based on other code and they were kind of struggling for some notion that was like this because they were talking about what they call types and subtypes and by which they meant you know a stack is a type file system as such the files of type there were many things like that and they were interested in you know what's the subtype of a of a queue like thing you know there's a stack there's a specific fight from keyword so forth and so they were clearly looking for these definitions but they didn't have it right and they were very confused and in fact their description of the behavior of classes was often implementation driven it's like this but you change this implementation yeah and so hopefully that's not but so I'm trying to remember where I was right so I read these papers right and I realized they you know we're looking for something they didn't have and it was clear to me what it needed to be it was just a sort of a common-sense idea yes and so I the toughest they thought well you know maybe coming from my background and data abstraction I was able to see it and because they weren't thinking in those terms and I see one of these implementation terms and so I gave the keynote at Upsala and and later I wrote up a paper describing it which was never actually published except in I mean later a year ten years later mr. paper but at that time no and but it just the ideas took out like wildfire because they were really looking for it and I discovered in the 90s when somebody wrote me an email they asked is this the correct definition of the Cisco substitution principle and I didn't even know there was such a thing the name was invented it was on the internet everybody was talking about it earlier yeah and then later I was working with Jeannette wing we wrote some papers to come out with precise definitions of what it was well I think oh okay thank you very much oh you're welcome
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