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Theory of Databases

Explore mathematical, scientific, and cognitive views of the theory of databases. Discuss practical computing principles and cognitive implications.

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Theory of Databases

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  1. Theory of Databases • Module lecturer: Dr Meurig Beynon, Room 3.15 • Module Content • Generalities on databases • Database models: Theory and Practice • Entity-relationship models • Relational models: algebraic and logical • Commercial relational languages CS319 Theory of Databases

  2. CS319 Theory of Databases • Module Content (cont.) • Technical Issues and Algorithms • Optimisation • Integrity constraints • Database design • Future Trends: Theory and Practice • Object-oriented models • Extended relational systems • The Relational Model and SQL CS319 Theory of Databases

  3. Theory in Computer Science? • Theory in computer science is typically viewed as • - associated with formal foundations for computing • - based on mathematics (can there be any other kind of theory?) • - used to justify and to inform practical principles CS319 Theory of Databases

  4. Common perceptions about theory of CS • Computer Science means accounting for computing practice using mathematical theory • Mathematical theory is the essential foundation: practical computing is its application • The mathematical foundations of computer science are the bedrock of the subject - they frame computing in an abstract manner independent of technologies, and how these abstractions are realised in practice is a relatively ephemeral concern CS319 Theory of Databases

  5. Ephemeral conveys a number of ideas: • temporary • reflecting a current situation or fashion • not of abiding interest • of subordinate significance CS319 Theory of Databases

  6. In support of this view of theory … • From a mathematical perspective … • have a powerful abstract theory of computation: all programming platforms are Turing equivalent in some fundamental sense • it is difficult to know what meaning to attach to computational activity for which there is no abstract mathematical model • computation has - and always has had - a crucial role in mathematics itself CS319 Theory of Databases

  7. In support of this view of theory … • From a broader scientific perspective … • It is possible to regard pure sciences such as physics as establishing an intimate association between mathematical models and our interaction with the natural world • CS might plausibly be viewed as an embryonic Science of the Artificial, and we might expect abstract mathematical models to be ideally suited to framing such a discipline CS319 Theory of Databases

  8. In support of this view of theory … • From a cognitive perspective … • reasoning is an important constituent of human thought - logic is seen by many computer / cognitive scientists as the essential constituent of human intelligence, and the computer as an appropriate metaphor for the brain • cf. the logicist perspective on artificial intelligence … CS319 Theory of Databases

  9. Contrary to this view … • Theory has yet to deliver programming tools and principles that meet practical computing needs comprehensively • Functional programming • Formal models of concurrency • Formal methods for software development • … represent a partial solution to practical issues CS319 Theory of Databases

  10. Contrary to this view … • Crucial aspects of practical computing have no satisfactory supporting formal theory • human-computer interaction • end-user programming • object-oriented modelling • object-oriented software development • … mathematical models are of limited value CS319 Theory of Databases

  11. Contrary to this view … • Some of the most significant aspects of computing practice are pre-theory and subjective in character • Consider the observation and experiment involved e.g. • in requirements capture • in customising interfaces for personal use • in software development based on prototyping • … implicit knowledge embodied in interaction not explicit in mathematical models CS319 Theory of Databases

  12. Contrary to this view … • Interaction in the world can only be viewed as accounted for by theory if we accept a reductionist stance on the nature of science: consider the implications / meta-implications of a Theory of Everything in physics • Many aspects of human activity and interaction in the world [arguably] involve more than applications of logic: interaction in the world can be viewed as conceptually prior to reasoning, and not explicable in terms of logic: consider e.g. Rodney Brooks's robotics research on themes such as Intelligence without Reason, Intelligence without Representation CS319 Theory of Databases

  13. Contrary to this view … • Modern developments of computing challenge the mind-body dualism that underlies the idea of the brain as a complex computational device that can be conceptually separated from its embodiment: consider e.g. • - brain-mediated communication • - meaning as situated • - context dependence in natural language • Mathematics does not account for situated meaning CS319 Theory of Databases

  14. Two possible approaches to developing CS • [evolutionary] accept that there is an essential duality within computing that distinguishes the hard core science of computing from the soft ephemeral pseudo-science of computing practice, and focus on developing and extending classical theories with a view to giving as comprehensive an account of computing practice as is possible • [revolutionary] recognise that computer science as classically conceived is inadequate as a foundation for practical computing and artificial intelligence, and that this inadequacy cannot be resolved without reappraising the whole issue of how mathematical models and activities in the world are connected CS319 Theory of Databases

  15. Scope of CS 319 • Will use data modelling principles for databases as the arena within which to explore these broad issues concerning the role of theory in computer science • Complementary to other modules, e.g. that concern • formal approaches to software development • artificial intelligence • robotics • … personal views beyond scope of CS319 developed in CS405 An Introduction to Empirical Modelling CS319 Theory of Databases

  16. The principal theme of CS319 • How do theory and computing practice relate with specific reference to databases? • Key ideas: • The counterpart of the classical theory of computation in databases is Codd's relational theory. • There is an excellent correspondence between relational theory and practical database application of a certain kind. • Relational databases can be seen as a precursor for two principal kinds of computer application: environments for end-user programming and computer-based models of real-world state. CS319 Theory of Databases

  17. The principal theme of CS319 • How do theory and computing practice relate with specific reference to databases? • Key ideas (cont.): • There are aspects to the relational theory (especially those concerned with database design) that challenge the classical view of how an abstract mathematical model represents a situation in the world. • Modern database applications oblige us to question the adequacy of relational theory, and to consider the extent to which a relational framework can cope with notions such as objects, interfaces and agents. CS319 Theory of Databases

  18. Content of CS319 • To put the key ideas in perspective, address the following topics: • An extended account of relational theory and its applications in respect of the development of relational query language and database design. • The qualities of the relational model both as it was first conceived by Codd and as it has (and has not) been embodied in practical relational databases. CS319 Theory of Databases

  19. Content of CS319 • A critical assessment of the relational database model from the proponents of alternative kinds of database, such as object-oriented and extended relational models. • The possible limitations of the relational model where modern computing applications and technologies are concerned. • An evaluation of the various database model critiques and a personal perspective on the future of databases. CS319 Theory of Databases

  20. Aspects of a Computer Science education … • Three kinds of activity involved in learning CS • learning theory • gaining practical knowledge and skills of computing • developing a critical appreciation of how theory and practice are related • Principal emphasis in CS319 is on the first and third aspects … CS319 Theory of Databases

  21. Special lecture arrangements weeks 18 and 19 • Dr Hugh Darwenwas an IBM consultant on databases: • he is our guest lecturer in weeks 18 and 19 • NOTE: the lectures in week 18will be on The Relational Model and SQL thus: • Monday February 21st at 2pm and 5pm in CS1.04 • Thursday February 24th at 2pm and 5pm in CS1.04 • the lectures in week 19will be on • Temporal Data and the Relational Model thus: • Monday February 28th at 2pm and 5pm in CS1.04 • Thursday March 3rd at 2pm and 5pm in CS1.04 CS319 Theory of Databases

  22. Some context for the Theory of Databases Setting the scene Industrial perspectives Academic perspectives Sources for the CS319 module CS319 Theory of Databases

  23. Setting the scene for the theory of databases - relations • M J Ridley, University of Bradford (TLAD WS 2003) • DB systems or DB theory – or “Why don’t you teach ORACLE” • “The modern age of databases may [NB! - WMB] have started with relational databases which despite their ubiquitous nature we should remember were looked an as of only academic interest at one time. What surely marks this era [the early 1970s] out is the sound theoretical basis of that database model and the progress that was made because of this. • … But what age are we in now?” CS319 Theory of Databases

  24. Setting the scene for the theory of databases - objects • Object oriented DBs emerged in the 1980s in response to the feeling that relational databases were inadequate for certain classes of applications ... • Disadvantages of OODBs • Brown, A.W. OODBs: Applications in S/W Engineering, 1991 • no formal semantics • loss of relational simplicity • navigational queries • no general query language CS319 Theory of Databases

  25. Setting the scene for the theory of databases – obj+rel • Object oriented DBs emerged in the 1980s in response to the feeling that relational databases were inadequate for certain classes of applications ... The extent to which object-oriented and relational DBs can be unified, as in ‘object-relational’ DBs, remains controversial • Ridley cites Maier (2002) on object-relational systems: • David Maier speaks out, SIGMOD Record, 31(4), 2002 http://www.acm.org/sigmod/record/issues/0212/ • “there’s not a good design theory the way there was [with] normal form relations for relational databases” • “… [the new features] at least [double] the number of [design] choices you have in every instance …” CS319 Theory of Databases

  26. Setting the scene for the theory of databases – the Web • Ridley observes: The Web has made many more people database users and heightened the awareness of databases generally … it raises the issues of the semantic mismatch between the set oriented nature of SQL and most programming languages. … cites: • The Asilomar report on Database Research, SIGMOD Record, 27(4), 1998 http://www.acm.org/sigmod/record/issues/9812/ • “Theorem: The WEB changes everything. • Corollary: XML is the means” • … and raises the question: • But where then is our dominant relational paradigm left? CS319 Theory of Databases

  27. Perspectives from the computing industry 1 • From “Whatever happened to OODBs?” • http://www.leavcom/db_08_00.html • “[In 1998] industry experts touted OODBs as a technology on the rise, well suited for the emerging Internet age … [OODBs] would soon become the primary DB technology, supplanting RDBMSs, which were not designed to handle multimedia data … Fast forward to today, and … RDBs are still by far the most widely used DBs … meanwhile, object-relational DBMSs have added object capabilities to relational DBs … they are gaining popularity and are expected to outsell even RDBs by 2003 …” CS319 Theory of Databases

  28. Perspectives from the computing industry 2 • Rick Catell (SUN Microsystems): “Object-oriented DBs are doing just fine, and the news of their demise is greatly exaggerated. While their market isn’t as big, they continue to be used in areas like CAD (computer-aided design) and telecommunications, where RDBMSs are not well suited.” • Michael Stonebraker (Informix): “ODBMSs occupy a small niche market that has no broad appeal. The technology is in semi-rigor mortis, andORDBMSs will corner the market within five years.” • [quotations dating from around the year 2000] CS319 Theory of Databases

  29. Perspectives from the computing industry 3 • International Data Corporation Opinion • from OODB vs ORDBs, Steve McClure, 1997 • “Because of the relative size of the RDBMS vendors’ marketing infrastructures, the ORDBMS market will surpass the size of the ODBMS market in the next five years. Nevertheless, putting object-oriented extensions on RDBMSs is tantamount to adding stereo radios and global navigation systems to horse-drawn carriages. You will have interesting enhancements, but the wrong base vehicle. In the end it won’t be an appropriate vehicle for the information superhighway.” CS319 Theory of Databases

  30. Perspectives from academia 1 • M J Ridley, University of Bradford (TLAD WS 2003) • DB systems or DB theory – or “Why don’t you teach ORACLE” • “Practice without Theory is blind, Theory without Practice is sterile” (Karl Marx) • “… most people would agree [that] … we need a theoretical framework in which to talk about DBs if the result is to be productive … The questions that seem to me to need answering are: What is that framework? … “ CS319 Theory of Databases

  31. Perspectives from academia 2 • M J Ridley, University of Bradford (TLAD WS 2003) • DB systems or DB theory – or “Why don’t you teach ORACLE” • “… most people would agree [that] … we need a theoretical framework in which to talk about DBs if the result is to be productive …The questions that seem to me to need answering are: What is that framework? • … Is it the simple relational model? How important is that framework? (In practical, educational terms how much of the syllabus is this?) Are there competing theoretical frameworks that need considering?” CS319 Theory of Databases

  32. Perspectives from academia 3 • M J Ridley, University of Bradford (TLAD WS 2003) • DB systems or DB theory – or “Why don’t you teach ORACLE” • “… most people would agree [that] … we need a theoretical framework in which to talk about DBs if the result is to be productive … • But is there still a firm theoretical foundation for what we teach? Does that matter? Are we in danger of training students in the features of a particular system (and a convenient web interface for it) rather than educating them about DBs in the broader sense? …” CS319 Theory of Databases

  33. Perspectives from academia 4 • M J Ridley, University of Bradford (TLAD WS 2003) • DB systems or DB theory – or “Why don’t you teach ORACLE” • “What is the relationship of Database teaching to other aspects of the curriculum such as the study of data structures and object-orientation? And are there theories of these subjects? … ” • “… is there are more general object theory that informs programming and software development generally. If so can relational theory be located as a subset of that mainstream or does database stand out as an exception?” CS319 Theory of Databases

  34. Perspectives from academia 5 • M J Ridley, University of Bradford (TLAD WS 2003) • DB systems or DB theory – or “Why don’t you teach ORACLE” • Ridley’s own answer to these questions: • “… we are in danger of losing sight of firm theoretical ground especially as we are under pressure to include yet more additional facilities of DBMSs … more so as object systems have failed to achieve commercial success commensurate with their early promise and the pressure of the web has shifted the focus of much database work.” CS319 Theory of Databases

  35. Books on Classical Relational Databases • Date, C.J. A Database Primer, Addison-Wesley • Date, C.J. An Introduction to Database Systems, Addison-Wesley 8th edition, 2003 • Ullman, J.D. Principles of Database Systems 2nd edition, Computer Science Press 1982 • Ullman, J.D. Principles of Database & Knowledge-base Systems Vols 1 & 2, Computer Science Press 1988 • Ullman, J.D. A First Course in Database Systems, 2nd ed Prentice-Hall, 2002 • … see http://www-db.stanford.edu/~ullman/ullman-books.html CS319 Theory of Databases

  36. Books on more general database issues • Korth, H.F. and Silberschatz Database System Concepts, McGraw-Hill 2nd ed. 1991, 4th ed. 2001 • Brown, A.W. Object-oriented Databases: Applications in Software Engineering, McGraw-Hill International Series in Engineering, 1991 • Gray, P.D. Logic, Algebra & Databases, Ellis-Horwood Series, Computers and their Applications 29 • Kent, William Data and Reality: basic assumptions in data processing reconsidered, North-Holland 1987 CS319 Theory of Databases

  37. Books on Relational Theory in its application • Date, C.J. Relational Database Writings 1985-1989 Addison-Wesley [and other collections in this series] • Hugh Darwen and C.J.Date Foundations for Object/Relational Databases: The Third Manifesto 1998 Harlow, Addison-Wesley Longman • C.J.Date, Hugh Darwen, M.A.Lorentzos Temporal Data and the Relational Model, Morgan-Kaufmann, 2002 • (summarised in Chap. 23 of Date’s Intro to DBs, 8th ed) • Dr Hugh Darwen was an IBM consultant on database • until his retirement in 2004: he is our guest lecturer in • weeks 18 and 19 CS319 Theory of Databases

  38. Special lecture arrangements weeks 18 and 19 • Dr Hugh Darwenwas an IBM consultant on databases: • he is our guest lecturer in weeks 18 and 19 • NOTE: the lectures in week 18will be on The Relational Model and SQL thus: • Monday February 21st at 2pm and 5pm in CS1.04 • Thursday February 24th at 2pm and 5pm in CS1.04 • the lectures in week 19will be on • Temporal Data and the Relational Model thus: • Monday February 28th at 2pm and 5pm in CS1.04 • Thursday March 3rd at 2pm and 5pm in CS1.04 CS319 Theory of Databases

  39. Questions regarding status of DB theory 1 • Issues about the context in which DB theory applies: • To what extent do theories about databases in general apply ‘exclusively’ to relational databases? • To what extent is DB theory specific to applications? • - technology / kind of activity / nature of environment • … it applies to the 1970s business context … does it apply now? CS319 Theory of Databases

  40. Questions regarding status of DB theory 2 • Issues about the scope and nature of DB theory itself: • How does DB theory relate to objectives such as • - supporting end-user programming? • - representing real-world state? • How does DB theory relate to other conceptual frameworks (e.g. data modelling in OO / UML / ER) • to address broader issues (e.g. typing / non-procedural vs procedural models of computation)? CS319 Theory of Databases

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