Memorial Tributes: Volume 27
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  • ARAVIND K. JOSHI (1929-2017)



    ARAVIND KRISHNA JOSHI, the Henry Salvatori Professor Emeritus of Computer and Cognitive Science, passed away December 31, 2017, in his home in Philadelphia. He was 88 years old. His research transformed formal understanding of human language.

    Aravind was born August 5, 1929, in Pune, India. Growing up in a multilingual country, he noted that “you can’t avoid but learn three or four languages, and then of course English…. There is something mysterious about language, so I was always interested in it.” At the University of Pune he earned a bachelor of engineering degree in electrical and mechanical engineering (1950), and then from the Indian Institute of Science, in Bangalore, he received a graduate diploma, the equivalent of a master’s degree, in communications engineering (1952). Two years later he immigrated to the United States and worked at RCA Camden (a budget label of RCA Victor) (1954–58) while working toward a master’s degree in electrical engineering at the University of Pennsylvania (1958). He stayed at Penn for his PhD (1960) and then was appointed an assistant professor in the university’s Moore School of Electrical Engineering. He remained at Penn for the rest of his career.

    Aravind shifted from his PhD research in information theory and communication theory to work on problems at the intersection of formal linguistics and computer science. He was a research assistant in a group under the linguist Zellig Harris (NAS 1973) for several years, leading to the development in 1959 of one of the very first automatic natural language parsers. Thus began Aravind’s lifelong commitment to interdisciplinary work in what came to be called cognitive science.

    After a secondary appointment in linguistics (1964) he joined the newly formed graduate group in computer and information science at the Moore School and was promoted to associate professor with tenure in 1967. In 1972 he was instrumental in the foundation of the Department of Computer and Information Science (CIS) and became its first chair immediately after becoming a full professor. During his 13 years as chair, he played a central role in creating the department’s respectful, interdisci­plinary culture. He was appointed the Henry Salvatori Professor of Computer and Cognitive Science in 1983.

    Aravind stood first among his colleagues in CIS in wisdom and insight. Many impassioned arguments in faculty meetings disappeared when Aravind, after listening in silence, calmly said just the right few words.

    He taught courses in information theory, probability and statistics, and coding theory until 1965. Then his teaching followed his research interests in formal language and automata theory, mathematical linguistics, natural language pro­cessing, and artificial intelligence.

    In 1978 his success in strengthening cognitive science across relevant departments led to the creation of a formal program in cognitive science at Penn funded by the Alfred P. Sloan Foundation. His passion for interdisciplinary cognitive science was contagious, and in the mid-1980s he convinced the dean of engineering, Joe Bordogna, to seed Penn’s first position in linguistic semantics in the Department of Linguistics—outside of engineering because of the importance of semantics to natural language technology.

    In 1990 Aravind cofounded, with Lila R. Gleitman (NAS), the Institute for Research in Cognitive Science (IRCS), which soon became the site of Penn’s first Science and Technology Center and thrived for the following 25 years, training an entire generation of researchers in a highly interdisciplinary take on cognitive science. The institute also served as the home of Penn’s cognitive science major, which now enrolls over 100 undergraduates each year. Aravind served as IRCS codirector until 2002.

    Aravind’s contributions to mathematical, computational, and empirical linguistics are both broad and deep, as illustrated in the following examples.

    Perhaps the best known of his contributions is the development of the tree adjunct grammar (TAG) formalism.1 In both natural language processing and theoretical linguistics, his work on TAG stands as a monument to the value of principled mathematical thinking. Two key ideas underlie this formalism: (1) that the statement of local syntactic and semantic dependencies can be factored separately from the recursion that characterizes context-free grammars, and (2) most unexpectedly, that a very modest increase in power beyond context-free grammar is sufficient to characterize the syntax of all existing natural languages. The TAG adjoining operation, as de-fined by Joshi, captures these in a strikingly elegant way, providing a powerful tool for linguistic description that at the same time yields grammars guaranteed to be computationally tractable.

    A significant body of work by Joshi and numerous others has continued to develop the consequences of his original insight for more than four decades. TAG has been applied to the difficult problems of developing practical grammars for online grammatical analysis, automatic practical natural language generation, semantic inter­pretation, and machine translation. Surprisingly, TAGs provide a robust framework for describing the structures of various kinds of transfer RNAs; these models were applied in the search for less temperature sensitive covid vaccines.

    A second major contribution lies in centering theory,2 a formal theory developed by Joshi and collaborators of what makes multisentence discourses coherent. Centering theory has important implications for automatic text generation, summarization, and dialogue systems. It provides a formal model of what makes one entity mentioned in a discourse more prominent than another, how shifts in prominence can be achieved in a text, and the consequences of prominence for what entities can be referred to by pronouns in a text. It has become a leading theory of discourse coherence in both computational linguistics and linguistic pragmatics. Aravind’s interest in discourse later led to the development of the Penn Discourse Treebank, a large-scale corpus annotated with discourse structure that is even now fostering new empirical investigations into discourse phenomena.

    His work in other aspects of mathematical linguistics has had a meaningful impact on linguistic theory. For example, he greatly generalized an earlier result to show that using powerful context-sensitive predicates as filters on the tree outputs of a context-free grammar still left the resulting language context free. This generalization then directly powered the best attempt to date to build a fully context-free grammar for natural languages.

    Throughout his career, Aravind developed academic communities by fostering the broadest possible participation by researchers in different domains and with different orientations. He was among the founding fellows of both the Association for the Advancement of Artificial Intelligence (AAAI) in 1990 and the Association of Compu­tational Linguistics in 2012.

    He emphasized the importance of educating young researchers and of supporting them morally and materially. He supervised over 35 PhD dissertations on topics ranging from information and coding theory to pure linguistics and was beloved by his students and his colleagues. Out of their admiration for him, over 100 students, alumni, and colleagues came together—from the around the country and abroad, from both academia and industry—for a day-long “Joshifest” in October 2012 to celebrate Aravind’s 52 years of contributions with attendees across the cognitive sciences and other fields. In 2001 the Aravind K. Joshi Assistant Professorship in Computer and Information Science was endowed by Silicon Valley entrepreneur and former student Jerry Kaplan.

    He advocated without fanfare for women in computer science. His first hire was the first female faculty member in Penn engineering—she succeeded Aravind as department chair. Two of the women whose graduate work he supervised went on to chair major computer science departments, and one, along with Aravind, was named a founding fellow of the Association for Computational Linguistics.

    In addition, he was dedicated to helping young Indian women with socioeconomic challenges, and provided funding to educate young women from areas outlying Pune to become economically independent. For one group in Pune, the Bhagini Nivedita Pratishthan, he, and subsequently his daughters, established a scholarship fund in his name for a succession of young women to complete their master’s degree.

    Long recognized for his work, he was named a Guggenheim Fellow in 1971 and a fellow of the Institute of Electrical and Electronics Engineers in 1976 and of the Association for Computing Machinery in 1998. His research accolades include the Best Paper Award at the National AAAI Conference in 1987. He was elected to the National Academy of Engineering in 1999, and received honorary doctorates from University of Paris 7 in 2002 and from Charles University, Prague, in 2017.

    He received nearly every major award in the fields of artificial intelligence, cognitive science, and computational linguistics. His honors include the Award for Research Excellence (1997) from the International Joint Conferences on Artificial Intelligence Organization, the first Association for Computational Linguistics Lifetime Achievement Award (2002), the David E. Rumelhart Prize of the Cognitive Science Society (2003), and the Benjamin Franklin Medal in Computer and Cognitive Science (2005).

    Aravind enjoyed his community and neighbors in West Philadelphia. He appreciated the rich musical and artistic environment in Philadelphia and was particularly fond of chamber music. The Joshi house was always open to students and colleagues, who over the years witnessed many parties. When his daughters were still young, he and his wife bought land in rural upstate Pennsylvania and built a simple cabin there. This became a peaceful oasis where Aravind made friends with the local dairy farmers and delighted in the fruits and vegetables of the local Amish community.

    He is survived by his wife of 54 years, Susan Heyner, daughters Shyamala Joshi and Meera Joshi, and two grandchildren.

    1Joshi AK, Levy LS, Takahashi M. 1975. Tree adjunct grammars. Journal of Computer and System Sciences 10(1):136–63.
    2Grosz BJ, Joshi AK, Weinstein S. 1995. Centering: A Framework for Modelling the Local Coherence of Discourse. University of Pennsylvania Institute for Research in Cognitive Science Technical Report No. IRCS-95-01.