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By C. J. Date


Myself when young did eagerly frequent Doctor and Saint, and heard great Argument About it and about; but evermore Came out by the same Door as in I went. —Edward Fitzgerald: The Rubáiyát of Omar Khayyam The Third Manifesto, by Hugh Darwen and myself ("the Manifesto " for short), lays down a set of prescriptions and proscriptions regarding the design of a database programming language it calls D (see reference [9]). One prescription in particular—"OO Prescription 3"—reads as follows: D shall be computationally complete. That is, D may support, but shall not require, invocation from so-called host programs written in languages other than D. Similarly, D may support, but shall not require, the use of other languages for implementation of userdefined operators. However, reference [1] argues that this prescription implies that the Manifesto is deeply flawed. To quote: 1 It's an error to make Tutorial D computationally complete because it creates a language with logical expressions that are provably not decidable—yet a decision procedure must exist for any logical expression to be evaluated. Note: This quote refers to Tutorial D, not D as such, so I need to explain how Tutorial D relates to D. To begin with, the name D is generic—it's used in reference [9] to refer generically to any language that conforms to the principles laid down in The Third Manifesto. Thus, there could be any number of distinct languages all qualifying as a valid D. Tutorial D is intended to 1 For reasons of clarity and flow I've edited most of the quotes in this paper, sometimes drastically so. be one such; it's defined more or less formally in reference [9], and it's used throughout that book (and elsewhere) as a basis for examples. For definiteness I'll concentrate on Tutorial D myself (mostly) in the present paper, since that's what reference [1] does, but the discussions and arguments actually apply to any valid D. Decidabilit

Topics: Computational completeness
Year: 2006
OAI identifier: oai:CiteSeerX.psu:
Provided by: CiteSeerX
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