The Early Days of Logic Programming:
a Personal Perspective

Veronica Dahl
Simon Fraser University

Editor: Enrico Pontelli

When I arrived at Luminy in 1975, Alain Colmerauer had just completed his article "Les grammaires de metamorphose", Dave H. D. Warren, Luís Moniz Pereira and Fernando Pereira were turning Prolog, from its first proof-of-concept implementation by Philippe Roussel, into a practical language, and the prof-to-student ratio was unbeatable: just five of us grads were in the DEA programme, of which only one ventured into the newly created Doctorat en Intelligence Artificielle.

Luminy - luminous, luminaries. I had chosen well. I wasn’t one more number in some huge impersonal lab. Luminous indeed it was, from the hope-filled sun rays that enlivened the hospital room where serious illness confined me upon arrival, to the splendid blue spaces of sea and sky that greeted my recovery two and a half weeks later.

My new friends Cristina and Michel van Caneghem had taken me through narrow, thyme-scented paths, tumbling down rock slides, gliding down from tree-tops on Tarzan-style ropes, and past dizzying precipices, until at one breathtaking turn, there they were: the Calanques, their white aching beauty shining againt the calm Mediterranean.

As I write these lines, trying to trace the spirit of the early LP days, it strikes me that the sense of freedom and unending peace that the Calanques conveyed must have insensibly permeated all our unconscious minds, and that the LP quest that I characterized as that of truth and beauty, as instigated by Alain Colmerauer and Bob Kowalski [1] is also, and fundamentally, a quest for freedom: from procedural concerns, from the tyranny of time's sequential nature, and more recently, even from the limitations of its own roots in classical logic.

Soon, I was accepted into the group as "one more guy" - a dubious honour! I would for instance arrive at my office to the sight of one of my companions sitting in his underwear while his pants dried out from an unexpected rain Smile

But to be frank, I had been lying through my teeth when Alain, visiting me at the hospital, had asked me whether I would continue into the doctoral programme. I felt obliged to say yes to be taken seriously, yet I doubted I would have the patience and stamina needed. I was merely taking distance for one year from my country's incipient death squads, which had just killed a dear friend. In impotent counterpoint to the escalating violence in Argentina, as many more friends were murdered or disappeared, and my mother was declared "a real or potential danger to the security of the state" after the military coup, the Calanques became my physical refuge, and LP perhaps a mental one, both symbolizing resilience, life, freedom.

Those early days' obsession with ever higher levels of freedom was sustained by the remarkable stubbornness of the free spirits behind LP, in defiance of the rest of the world's general belief that automated proof had revealed its limitations and could not yield much of practical value. These traits in fact continue to characterize our field, which abounds in survivors of sorts, like Catuscia Palamidessi who persisted studying despite nine years of daily pressure from her family environment to not "waste" her time in academia and secure a husband instead, or Manuel Hermenegildo who during his military service daily tested with his life whether a surreptitious bomb had been placed in his commander's vehicle, or Hassan Ait-Kaci who survived grad studies while single parenting his baby.

My passion for the Calanques soon converted me in the group's unofficial guide for visitors, adding a more human dimension to my image of scientific "monsters": for instance, Dave H. D. Warren's questions while hiking with a baby on his backpack were somehow less intimidating than when he'd "grilled me" after my talk at Imperial College.

I'd lucked out again: I happened to be at Alain's office when Bob called to invite him to an informal workshop he was organizing. As Alain was regretting that no one in the group could attend, I was jumping up and down volunteering: Moi! Moi! I can go!

So the group sent a student to present at Imperial College her joint DEA work with Roland Sambuc: a French-consultable expert system with dynamic coroutining of the tasks implicit in a user's query, which postponed executing negative goals under negation as failure until all necessary instantiations had been made. It was  great to hear Bob's talk on n-ary vs. binary relationships, Keith's on what is now known as Clark's completion theory, and above all, to meet so many excellent researchers in person.

Towards my dream of building a bridge between the humanistic and the formal sciences, I had been studying Linguistics at the Faculty of Philosophy and Letters in Buenos Aires, as I thought it might provide a good starting point, being the most formalized of the human sciences. This dream never quite materialized, but over the years, with LP enlisted into pursuing it, good results nevertheless poured on my lap for language processing and logic grammars, and extended into unexpected fields, e.g. computational molecular biology, where logic grammars were used for helping find the human genome, for the automatic analysis of biological sequences and for RNA secondary structure design; internet technology, with results in guided and long-distance learning, acronym meaning reconstruction and multilingual access to virtual worlds; and constraint based reasoning, where initial results for language parsing proved also useful for cognitive theory, error detection and correction, and knowledge extraction from text. More recently, I have been focussing on extending Prolog with non-classical lines of reasoning such as abduction and assumptions.

Perhaps one day all these incursions into apparently disparate fields will integrate into realizing my initial dream, and perhaps that will contribute to a less dichotomized, maybe even more peaceful world.

Acknowledgements: As in Claire Bretecher's comic, I could dedicate these memoirs "to him to whom I owe everything", in the certainty that this would make lots of people happy. So if I forget to name anyone, please take that as the default dedication. My greatest debt is to Alain Colmerauer, a superb supervisor and an exceptional human being, and to the GIA members of the early years. Bob Kowalski and the colleagues who attended that fantastic first workshop at Imperial were particularly inspiring, as were the workshop on logic and databases organized by Herve Gallaire in Toulouse, Peter Szeredi's workshop in Debrecen, Luís Moniz Pereira's at Albufeira, and the symbolically and literally floating workshop on board of the Queen Mary, all leading to the established, more formal but equally fun and productive ICLP conferences. Luís Moniz Pereira and Helder Coelho, David H. D.Warren, Fernando Pereira, and later David Scott Warren helped spread the word re. my early Spanish system, which was ported into many languages and generated lots of further research.  Alan Robinson, to whom indeed we all owe everything, cheered me up when I needed it with his exceptional human quality, Bonnie Webber rescued my TODS submission from oblivion from an editor's forgotten pile, and the list goes on and on. Special thanks to my many wonderful collaborators from all over the globe: Harvey Abramson, Pablo Accuosto, Dulce Aguilar-Solis, Jamie Andrews, Joao Balsa, Alma Barranco-Mendoza, Maryam Bavarian, Gabriel Bès, Philippe Blache, Michel Boyer, Charles Brown, Joe Calder, Henning Christiansen, Silvia Clerici, Koen DeBosschere, Marcos Elinger, Andrew Fall, Baohua Gu, Eli Hagen, Jia Wei Han, Glendon Holst, Yan-Nong Huang, Alfredo Hurtado, Bharat Jayaraman, Andre Levesque, Renwei Li, Susana Lilliecreutz, Diane Massam, Pierre Massicotte, Michael Mc Cord, Luís Moniz Pereira, Lidia Moreno, Manuel Palomar, T. Pattabhiraman, Jose Gabriel Pereira-Lopes, Fred Popowich, Stephen Rochefort, Michael Rochemont, Roland Sambuc, Patrick Saint-Dizier, Greg Sidebottom, Marius Scurtescu, Paul Tarau, Marie-Claude Thomas, Stephen Tse, Jorg Ueberla, Kimberly Voll, Tom Yeh, Manuel Zahariev, Osmar Zaiane. And to all of you, free spirits of LP: my heartfelt thanks.

[1] ALP Newsletter 15-4, 2002 (