Skip to main content Accessibility help
Hostname: page-component-7ccbd9845f-mpxzb Total loading time: 1.143 Render date: 2023-02-01T03:22:34.448Z Has data issue: true Feature Flags: { "useRatesEcommerce": false } hasContentIssue true

Knowledge machines

Published online by Cambridge University Press:  15 August 2018

Paul Smart*
Electronics & Computer Science, University of Southampton, Southampton SO17 1BJ, UK e-mail:


The World Wide Web has had a notable impact on a variety of epistemically relevant activities, many of which lie at the heart of the discipline of knowledge engineering. Systems like Wikipedia, for example, have altered our views regarding the acquisition of knowledge, while citizen science systems such as Galaxy Zoo have arguably transformed our approach to knowledge discovery. Other Web-based systems have highlighted the ways in which the human social environment can be used to support the development of intelligent systems, either by contributing to the provision of epistemic resources or by helping to shape the profile of machine learning. In the present paper, such systems are referred to as knowledge machines. In addition to providing an overview of the knowledge machine concept, the present paper reviews a number of issues that are associated with the scientific and philosophical study of knowledge machines. These include the potential impact of knowledge machines for the theory and practice of knowledge engineering, the role of social participation in the realization of knowledge-based processes, and the role of standardized, semantically enriched data formats in supporting the ad hoc assembly of special-purpose knowledge systems and knowledge processing pipelines.

Survey Article
© Cambridge University Press, 2018 

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)


Auer, S., Bizer, C., Kobilarov, G., Lehmann, J., Cyganiak, R. & Ives, Z. 2007. DBpedia: a nucleus for a Web of open data. Lecture Notes in Computer Science 4825, 722735.CrossRefGoogle Scholar
Berners-Lee, T. & Fischetti, M. 1999. Weaving the Web: The Original Design and Ultimate Destiny of the World Wide Web. Harper Collins.Google Scholar
Berners-Lee, T., Hendler, J. & Lassila, O. 2001. The Semantic Web. Scientific American 284(4), 3443.CrossRefGoogle Scholar
Bonabeau, E. 2009. Decisions 2.0: the power of collective intelligence. MIT Sloan Management Review 50(2), 4552.Google Scholar
Bozzon, A., Brambilla, M., Ceri, S., Silvestri, M. & Vesci, G. 2013. Choosing the right crowd: expert finding in social networks. In 16th International Conference on Extending Database Technology, N. W. Paton, G. Guerrini, B. Catania, M. Castellanos, P. Atzeni, P. Fraternali & A. Gounaris(eds). ACM, 637–648.Google Scholar
Branson, S., Horn, G., Wah, C., Perona, P. & Belongie, S. 2014. The ignorant led by the blind: a hybrid human-machine vision system for fine-grained categorization. International Journal of Computer Vision 108(1), 329.Google Scholar
Cardamone, C., Schawinski, K., Sarzi, M., Bamford, S. P., Bennert, N., Urry, C. M., Lintott, C., Keel, W. C., Parejko, J. & Nichol, R. C. 2009. Galaxy Zoo Green Peas: discovery of a class of compact extremely star-forming galaxies. Monthly Notices of the Royal Astronomical Society 399(3), 11911205.CrossRefGoogle Scholar
Carter, A. J., Clark, A., Kallestrup, J., Palermos, O. S. & Pritchard, D. (eds) 2018. Socially Extended Epistemology. Oxford University Press.CrossRefGoogle Scholar
Caton, S., Hall, M. & Weinhardt, C. 2015. How do politicians use Facebook? An applied Social Observatory. Big Data & Society 2(2), 118.CrossRefGoogle Scholar
Clark, A. 2008. Supersizing the Mind: Embodiment, Action, and Cognitive Extension. Oxford University Press.CrossRefGoogle Scholar
Coburn, C. 2014. Play to cure: genes in space. Lancet Oncology 15(7), 688.CrossRefGoogle Scholar
Comesaña, J. 2011. Reliabilism. In The Routledge Companion to Epistemology, Bernecker, S. & Pritchard, D. (eds). Routledge, 176186.Google Scholar
Cooper, S., Khatib, F., Treuille, A., Barbero, J., Lee, J., Beenen, M., Leaver-Fay, A., Baker, D., Popovic, Z. & Foldit, Players 2010. Predicting protein structures with a multiplayer online game. Nature 466(7307), 756760.CrossRefGoogle ScholarPubMed
Crouser, R. J., Ottley, A. & Chang, R. 2013. Balancing human and machine contributions in human computation systems. in Handbook of Human Computation, Michelucci, P. (ed.). Springer, 615623.Google Scholar
Demartini, G. 2015. Hybrid human-machine information systems: challenges and opportunities. Computer Networks 90, 513.CrossRefGoogle Scholar
Fallis, D. 2008. Toward an epistemology of Wikipedia. Journal of the American Society for Information Science and Technology 59(10), 16621674.CrossRefGoogle Scholar
Fallis, D. 2011. Wikipistemology. in Social Epistemology: Essential Readings, Goldman, A. I. & Whitcomb, D. (eds). Oxford University Press, 297313.Google Scholar
Gaines, B. R. 2013. Knowledge acquisition: past, present and future. International Journal of Human-Computer Studies 71(2), 135156.CrossRefGoogle Scholar
Gao, H., Barbier, G. & Goolsby, R. 2011. Harnessing the crowdsourcing power of social media for disaster relief. IEEE Intelligent Systems 26(3), 1014.CrossRefGoogle Scholar
Gelernter, D. 1992. Mirror Worlds. Oxford University Press.Google Scholar
Giannotti, F., Pedreschi, D., Pentland, A., Lukowicz, P., Kossmann, D., Crowley, J. & Helbing, D. 2012. A planetary nervous system for social mining and collective awareness. The European Physical Journal Special Topics 214(1), 4975.CrossRefGoogle Scholar
Gil, Y. 2011. Interactive knowledge capture in the new millennium: how the Semantic Web changed everything. The Knowledge Engineering Review 26(1), 4551.CrossRefGoogle Scholar
Giles, J. 2005. Internet encyclopaedias go head to head. Nature 438(7070), 900901.CrossRefGoogle ScholarPubMed
Glennan, S. 2017. The New Mechanical Philosophy. Oxford University Press.CrossRefGoogle Scholar
Glennan, S. & Illari, P. M. (eds) 2018. The Routledge Handbook of Mechanisms and Mechanical Philosophy. Routledge.Google Scholar
Goldman, A. I. 1986. Epistemology and Cognition. Harvard University Press.Google Scholar
Goldman, A. I. 2002. Précis of knowledge in a social world. Philosophy and Phenomenological Research 64(1), 185190.CrossRefGoogle Scholar
Goldman, A. I. 2011. A guide to social epistemology. In Social Epistemology: Essential Readings, Goldman, A. I. & Whitcomb, D. (eds). Oxford University Press, 1137.Google Scholar
Goldman, A. I. 2012. Reliabilism and Contemporary Epistemology: Essays. Oxford University Press.CrossRefGoogle Scholar
Gomez-Perez, A., Fernandez-Lopez, M. & Corcho, O. 2004. Ontological Engineering. Springer.Google Scholar
Good, B. M. & Su, A. I. 2011. Games with a scientific purpose. Genome Biology 12(135), 13.CrossRefGoogle ScholarPubMed
Greco, J. 2007. The nature of ability and the purpose of knowledge. Philosophical Issues 17(1), 5769.CrossRefGoogle Scholar
Greco, J. 2010. Achieving Knowledge: A Virtue-Theoretic Account of Epistemic Normativity. Cambridge University Press.CrossRefGoogle Scholar
Greco, J. 2012. A (different) virtue epistemology. Philosophy and Phenomenological Research 85(1), 126.CrossRefGoogle Scholar
Gruber, T. 2008. Collective knowledge systems: where the Social Web meets the Semantic Web. Web Semantics: Science, Services and Agents on the World Wide Web 6(1), 413.Google Scholar
Hart, A. 1986. Knowledge Acquisition for Expert Systems. Kogan Page.Google Scholar
Hayes-Roth, F., Waterman, D. A. & Lenat, D. B. 1983. Building Expert Systems. Addison-Wesley.Google Scholar
Hedström, P. 2005. Dissecting the Social: On the Principles of Analytical Sociology. Cambridge University Press.CrossRefGoogle Scholar
Hedström, P. & Ylikoski, P. 2010. Causal mechanisms in the social sciences. Annual Review of Sociology 36, 4967.CrossRefGoogle Scholar
Hendler, J. & Berners-Lee, T. 2010. From the Semantic Web to social machines: a research challenge for AI on the World Wide Web. Artificial Intelligence 174, 156161.CrossRefGoogle Scholar
Hendler, J. & Mulvehill, A. M. 2016. Social Machines: The Coming Collision of Artificial Intelligence, Social Networking, and Humanity. Apress.CrossRefGoogle Scholar
Heylighen, F. 2016a. Stigmergy as a universal coordination mechanism I: definition and components. Cognitive Systems Research 38, 413.CrossRefGoogle Scholar
Heylighen, F. 2016b. Stigmergy as a universal coordination mechanism II: varieties and evolution. Cognitive Systems Research 38, 5059.CrossRefGoogle Scholar
Hirsch, D. D. 2014. The glass house effect: big data, the new oil, and the power of analogy. Maine Law Review 66(2), 373395.Google Scholar
Hoffman, R. R. & Lintern, G. 2006. Eliciting and representing the knowledge of experts. In The Cambridge Handbook of Expertise and Expert Performance, Ericsson, K. A., Charness, N., Feltovich P. & Hoffman, R. R. (eds). Cambridge University Press, 165191.Google Scholar
Hooper, C., Bailey, B., Glaser, H. & Hendler, J. 2016. Social machines in practice: solutions, stakeholders and scopes. In 8th International ACM Web Science Conference, Nejdl, W., Hall, W., Parigi P. & S. Staab, (eds). ACM, 156–160.Google Scholar
Hutchins, E. 1995. Cognition in the Wild. MIT Press.Google Scholar
Kaiser, M. I. & Krickel, B. 2017. The metaphysics of constitutive mechanistic phenomena. The British Journal for the Philosophy of Science 68(3), 745779.Google Scholar
Kamar, E., Hacker, S. & Horvitz, E. 2012. Combining human and machine intelligence in large-scale crowdsourcing. In 11th International Conference on Autonomous Agents and Multiagent Systems, van der Hoek, W., Padgham, L., Conitzer, V. & Winikoff, M. (eds). 1, IFAAMAS 467–474.Google Scholar
Khatib, F., Cooper, S., Tyka, M. D., Xu, K., Makedon, I., Popovic, Z., Baker, D. & Foldit, Players 2011. Algorithm discovery by protein folding game players. Proceedings of the National Academy of Sciences 108(47), 1894918953.CrossRefGoogle ScholarPubMed
Khatib, F., DiMaio, F., Cooper, S., Kazmierczyk, M., Gilski, M., Krzywda, S., Zabranska, H., Pichova, I., Thompson, J., Popovic, Z., Jaskolski, M. & Baker, D. 2011. Crystal structure of a monomeric retroviral protease solved by protein folding game players. Nature Structural & Molecular Biology 18(10), 11751177.CrossRefGoogle ScholarPubMed
Kidd, A. L. (ed.) 1987. Knowledge Acquisition for Expert Systems: A Practical Handbook. Plenum Press.CrossRefGoogle Scholar
Kohl, N. E., Emini, E. A., Schleif, W. A., Davis, L. J., Heimbach, J. C., Dixon, R. A. F., Scolnick, E. M. & Sigal, I. S. 1988. Active human immunodeficiency virus protease is required for viral infectivity. Proceedings of the National Academy of Sciences 85(13), 46864690.CrossRefGoogle ScholarPubMed
Krötzsch, M., Vrandečić, D., Völkel, M., Haller, H. & Studer, R. 2007. Semantic Wikipedia. Journal of Web Semantics 5(4), 251261.CrossRefGoogle Scholar
Laszlo, P. 2004. Science as play. American Scientist 92(5), 398400.CrossRefGoogle Scholar
Law, E. & von Ahn, L. 2009. Input-agreement: a new mechanism for collecting data using human computation games. In SIGCHI Conference on Human Factors in Computing Systems, Olsen, D. R., Arthur, R. B., Hinckley, K., Morris, M. R., Hudson, S. & Greenberg, S. (eds). ACM, 1197–1206.Google Scholar
Lehmann, J., Isele, R., Jakob, M., Jentzsch, A., Kontokostas, D., Mendes, P. N., Hellmann, S., Morsey, M., van Kleef, P. & Auer, S. 2012. DBpedia—a large-scale, multilingual knowledge base extracted from Wikipedia. Semantic Web 6(2), 167195.Google Scholar
Lintott, C. J. & Reed, J. 2013. Human computation in citizen science. In Handbook of Human Computation, Michelucci, P. (ed.). Springer, 153162.CrossRefGoogle Scholar
Lintott, C. J., Schawinski, K., Keel, W., Van Arkel, H., Bennert, N., Edmondson, E., Thomas, D., Smith, D. J. B., Herbert, P. D., Jarvis, M. J., Virani, S., Andreescu, D., Bamford, S. P., Land, K., Murray, P., Nichol, R. C., Raddick, M. J., Slosar, A., Szalay, A. & Vandenberg, J. 2009. Galaxy Zoo: ‘Hanny's Voorwerp’, a quasar light echo? Monthly Notices of the Royal Astronomical Society 399(1), 129140.CrossRefGoogle Scholar
Lintott, C. J., Schawinski, K., Slosar, A., Land, K., Bamford, S., Thomas, D., Raddick, M. J., Nichol, R. C., Szalay, A., Andreescu, D., Murray, P. & van den Berg, J. 2008. Galaxy Zoo: morphologies derived from visual inspection of galaxies from the Sloan Digital Sky Survey. Monthly Notices of the Royal Astronomical Society 389(3), 11791189.Google Scholar
Malone, T. W., Laubacher, R. & Dellarocas, C. 2010. The collective intelligence genome. MIT Sloan Management Review 51(3), 2131.Google Scholar
Marsden, J. 2013. Stigmergic self-organization and the improvisation of Ushahidi. Cognitive Systems Research 21, 5264.CrossRefGoogle Scholar
McGonigal, J. 2011. Reality is Broken: Why Games Make us Better and How They Can Change the World. Penguin Books Ltd.Google Scholar
Mejova, Y., Weber, I. & Macy, M. W. (eds) 2015. Twitter: A Digital Socioscope. Cambridge University Press.CrossRefGoogle Scholar
Michaelian, K. 2014. JFGI: from distributed cognition to distributed reliabilism. Philosophical Issues 24(1), 314346.CrossRefGoogle Scholar
Michelucci, P. & Dickinson, J. L. 2016. The power of crowds. Science 351(6268), 3233.CrossRefGoogle ScholarPubMed
Morgan, J. 2016. Gaming for dementia research: a quest to save the brain. The Lancet Neurology 16(13), 1313.CrossRefGoogle Scholar
Myin, E. & O'Regan, J. K. 2009. Situated perception and sensation in vision and other modalities: a sensorimotor approach. In The Cambridge Handbook of Situated Cognition, Robbins, P. & Aydede, M. (eds). Cambridge University Press, 185200.Google Scholar
Okolloh, O. 2009. Ushahidi, or ‘testimony’: Web 2.0 tools for crowdsourcing crisis information. Participatory Learning and Action 59(1), 6570.Google Scholar
Palermos, O. & Pritchard, D. 2013. Extended knowledge and social epistemology. Social Epistemology Review and Reply Collective 2(8), 105120.Google Scholar
Palermos, S. O. 2015. Active externalism, virtue reliabilism and scientific knowledge. Synthese 192(9), 29552986.CrossRefGoogle Scholar
Palermos, S. O. 2017. Social machines: a philosophical engineering. Phenomenology and the Cognitive Sciences 16(5), 953978.CrossRefGoogle Scholar
Parunak, H. V. D. 2005. A survey of environments and mechanisms for human-human stigmergy. In International Workshop on Environments for Multi-Agent Systems’, Vol. 3830 of Lecture Notes in Artificial Intelligence, D. Weyns, P. H. V. Dyke & F. Michel (eds). Springer-Verlag, 163186.Google Scholar
Pritchard, D. 2009. Knowledge. Palgrave Macmillan.Google Scholar
Rzeszotarski, J. & Kittur, A. 2012. Crowdscape: interactively visualizing user behavior and output. In 25th Annual ACM Symposium on User Interface Software and Technology, Miller, R., Benko, H. & Latulipe, C. (eds). ACM, 55–62.Google Scholar
Savage, N. 2012. Gaining wisdom from crowds. Communications of the ACM 55(3), 1315.Google Scholar
Scekic, O., Truong, H.-L. & Dustdar, S. 2013. Incentives and rewarding in social computing. Communications of the ACM 56(6), 7282.CrossRefGoogle Scholar
Schreiber, G. 2013. Knowledge acquisition and the Web. International Journal of Human-Computer Studies 71(2), 206210.CrossRefGoogle Scholar
Schreiber, G., Akkermans, H., Anjewierden, A., de Hoog, R., Shadbolt, N. R., Van de Velde, W. & Weilinga, B. 2000. Knowledge Engineering and Management: The CommonKADS Methodology. MIT Press.Google Scholar
Schwamb, M. E., Orosz, J. A., Carter, J. A., Welsh, W. F., Fischer, D. A., Torres, G., Howard, W., Crepp, J. R., Keel, W. C. & Lintott, C. J. 2013. Planet Hunters: a transiting circumbinary planet in a quadruple star system. The Astrophysical Journal 768(127), 121.CrossRefGoogle Scholar
Shadbolt, N., Hall, W. & Berners-Lee, T. 2006. The Semantic Web revisited. IEEE Intelligent Systems 21(3), 96101.Google Scholar
Shadbolt, N., Van Kleek, M. & Binns, R. 2016. The rise of social machines: the development of a human/digital ecosystem. IEEE Consumer Electronics Magazine 5(2), 106111.CrossRefGoogle Scholar
Shadbolt, N. R. 2013. Knowledge acquisition and the rise of social machines. International Journal of Human-Computer Studies 71(2), 200205.CrossRefGoogle Scholar
Shadbolt, N. R. & Smart, P. R. 2015. Knowledge elicitation: methods, tools and techniques. In Evaluation of Human Work, 4th edition Wilson, J. R. & Sharples, S. (eds). CRC Press, 163200.Google Scholar
Simperl, E., Acosta, M. & Flock, F. 2013. Knowledge engineering via human computation. In Handbook of Human Computation, Michelucci, P. (ed.). Springer, 131151.CrossRefGoogle Scholar
Simperl, E. & Luczak-Rösch, M. 2014. Collaborative ontology engineering: a survey. The Knowledge Engineering Review 29(1), 101131.CrossRefGoogle Scholar
Simpson, R. J., Povich, M. S., Kendrew, S., Lintott, C. J., Bressert, E., Arvidsson, K., Cyganowski, C., Maddison, S., Schawinski, K. & Sherman, R. 2012. The Milky Way Project first data release: a bubblier galactic disc. Monthly Notices of the Royal Astronomical Society 424(4), 24422460.CrossRefGoogle Scholar
Siorpaes, K. & Hepp, M. 2008. Games with a purpose for the Semantic Web. IEEE Intelligent Systems 23(3), 5060.CrossRefGoogle Scholar
Smart, P. R., Huynh, T. D., Braines, D. & Shadbolt, N. R. 2010. Dynamic networks and distributed problem-solving. In Knowledge Systems for Coalition Operations (KSCO'10).Google Scholar
Smart, P. R. & Madaan, A. 2017. The social scaffolding of machine intelligence. International Journal On Advances in Intelligent Systems 10(3/4), 261279.Google Scholar
Smart, P. R. & Shadbolt, N. R. 2014. Social machines. In Encyclopedia of Information Science and Technology, Khosrow-Pour, M. (ed.). IGI Global, 68556862.Google Scholar
Smart, P. R., Simperl, E. & Shadbolt, N. R. 2014. A taxonomic framework for social machines. In Social Collective Intelligence: Combining the Powers of Humans and Machines to Build a Smarter Society, Miorandi, D., Maltese, V., Rovatsos, M., Nijholt A. & Stewart J. (eds). Springer, 5185.Google Scholar
Spiers, H. J., Manley, E., Silva, R., Conroy Dalton, T., Wiener, J. M., Hoolscher, C., Bohbot, V. & Hornberger, M. 2016. Spatial navigation ability assessed in over 1 million people globally. In Neuroscience.Google Scholar
Sterelny, K. 2003. Thought in a Hostile World: The Evolution of Human Cognition. Blackwell Publishing.Google Scholar
Steyvers, M. & Miller, B. 2015. Cognition and collective intelligence. In Malone, T. W. & Bernstein, M. S. (eds). Handbook of Collective Intelligence. MIT Press, 119137.Google Scholar
Strohmaier, M. & Wagner, C. 2014. Computational social science for the World Wide Web. IEEE Intelligent Systems 29(5), 8488.CrossRefGoogle Scholar
Studer, R., Benjamins, V. R. & Fensel, D. 1998. Knowledge engineering: principles and methods. Data & Knowledge Engineering 25(1), 161197.CrossRefGoogle Scholar
Sullivan, B. L., Aycrigg, J. L., Barry, J. H., Bonney, R. E., Bruns, N., Cooper, C. B., Damoulas, T., Dhondt, A. A., Dietterich, T. & Farnsworth, A. 2014. The eBird enterprise: an integrated approach to development and application of citizen science. Biological Conservation 169, 3140.Google Scholar
Sullivan, B. L., Wood, C. L., Iliff, M. J., Bonney, R. E., Fink, D. & Kelling, S. 2009. eBird: a citizen-based bird observation network in the biological sciences. Biological Conservation 142(10), 22822292.CrossRefGoogle Scholar
Sutton, J., Harris, C. B., Keil, P. G. & Barnier, A. J. 2010. The psychology of memory, extended cognition, and socially distributed remembering. Phenomenology and the Cognitive Sciences 9(4), 521560.CrossRefGoogle Scholar
Theraulaz, G. & Bonabeau, E. 1999. A brief history of stigmergy. Artificial Life 5(2), 97116.Google ScholarPubMed
Tinati, R., Wang, X., Tiropanis, T. & Hall, W. 2015. Building a real-time Web observatory. IEEE Internet Computing 19(6), 3645.CrossRefGoogle Scholar
Tiropanis, T., Hall, W., Shadbolt, N., De Roure, D., Contractor, N. & Hendler, J. 2013. The Web Science Observatory. IEEE Intelligent Systems 28(2), 100104.CrossRefGoogle Scholar
Tokarchuk, O., Cuel, R. & Zamarian, M. 2012. Analyzing crowd labor and designing incentives for humans in the loop. IEEE Internet Computing 16(5), 4551.CrossRefGoogle Scholar
Turner, J. S. 2011. Termites as models of swarm cognition. Swarm Intelligence 5(1), 1943.CrossRefGoogle Scholar
von Ahn, L. 2006. Games with a purpose. Computer 39(6), 9698.CrossRefGoogle Scholar
von Ahn, L. & Dabbish, L. 2004. Labeling images with a computer game. In SIGCHI Conference on Human Factors in Computing Systems, Dykstra-Erickson, E. & Tscheligi, M. (eds). ACM, 319–326.Google Scholar
von Ahn, L. & Dabbish, L. 2008. Designing games with a purpose. Communications of the ACM 51(8), 5867.CrossRefGoogle Scholar
Wang, J., Fischer, D. A., Barclay, T., Boyajian, T. S., Crepp, J. R., Schwamb, M. E., Lintott, C., Jek, K. J., Smith, A. M. & Parrish, M. 2013. Planet Hunters. V. A confirmed Jupiter-size planet in the habitable zone and 42 planet candidates from the Kepler archive data. The Astrophysical Journal 776(1), 118.CrossRefGoogle Scholar
Watson, D. & Floridi, L. 2018. Crowdsourced science: sociotechnical epistemology in the e-research paradigm. Synthese 195(2), 741764.CrossRefGoogle Scholar
Weld, D. S., Lin, C. H. & Bragg, J. 2015. Artificial intelligence and collective intelligence. In Handbook of Collective Intelligence, Malone, T. W. & Bernstein, M. S. (eds). MIT Press, 89114.Google Scholar
Cited by

Save article to Kindle

To save this article to your Kindle, first ensure is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.

Note you can select to save to either the or variations. ‘’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.

Find out more about the Kindle Personal Document Service.

Knowledge machines
Available formats

Save article to Dropbox

To save this article to your Dropbox account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you used this feature, you will be asked to authorise Cambridge Core to connect with your Dropbox account. Find out more about saving content to Dropbox.

Knowledge machines
Available formats

Save article to Google Drive

To save this article to your Google Drive account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you used this feature, you will be asked to authorise Cambridge Core to connect with your Google Drive account. Find out more about saving content to Google Drive.

Knowledge machines
Available formats

Reply to: Submit a response

Please enter your response.

Your details

Please enter a valid email address.

Conflicting interests

Do you have any conflicting interests? *