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Contents of /trunk/projects/dal/ADQL2Err1/ADQL2Err1.tex

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Wed Dec 17 13:20:50 2014 UTC (6 years, 7 months ago) by marco.merot@gmail.com
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First draft of the Errata Note on separator nonterminal (M.Molinaro)

1 \documentclass[11pt,a4paper]{ivoa}
2 \input tthdefs
4 \usepackage[utf8]{inputenc}
5 \usepackage{listings}
6 \lstloadlanguages{XML,sh}
8 \title{ADQL 2.0 Erratum 1: remove nonterminal separator grammar token}
10 \ivoagroup{Data Access Layer}
12 \author[http://wiki.ivoa.net/twiki/bin/view/IVOA/MarcoMolinaro]{Marco Molinaro}
13 \author[http://wiki.ivoa.net/twiki/bin/view/IVOA/IvoaDAL]{the IVOA DAL WG members}
15 \editor{Marco Molinaro}
17 % \previousversion[????URL????]{????Funny Label????}
18 \previousversion{This is the first public release}
20 \begin{document}
22 \begin{abstract}
23 This Erratum is intended to amend the ADQL-2.0 \citep{std:ADQL} recommendation removing the \xmlel{separator} token from the ADQL grammar. This amendation will both clarify the common usage of whitespaces and comments in current ADQL-2.0 and get closer to the SQL-92 \citep{std:SQL1992} standard upon which the ADQL is based.
24 \end{abstract}
26 \section*{Acknowledgments}
27 This Erratum takes direct input from the TAP Implementation Notes \citep{note:TAPNotes} and following discussions held at the Spring (ESAC, Spain) and Fall (Banff, Canada) 2014 IVOA Interoperability Meetings.
29 \section*{Conformance-related definitions}
31 The words ``MUST'', ``SHALL'', ``SHOULD'', ``MAY'', ``RECOMMENDED'', and
32 ``OPTIONAL'' (in upper or lower case) used in this document are to be
33 interpreted as described in IETF standard, \citet{std:RFC2119}.
35 The \emph{Virtual Observatory (VO)} is
36 general term for a collection of federated resources that can be used
37 to conduct astronomical research, education, and outreach.
38 The \href{http://www.ivoa.net}{International
39 Virtual Observatory Alliance (IVOA)} is a global
40 collaboration of separately funded projects to develop standards and
41 infrastructure that enable VO applications.
43 \section{Erratum Content}
44 The definition for the nonterminal \xmlel{separator} in the current ADQL-2.0 specification \citep{std:ADQL} is not clear, suggesting, with its only reference in the \xmlel{character\_string\_literal} that any ADQL language token may be followed by a separator and that nondelimiter tokens shall be followed by a delimiter token or a separator while the intention was probably to let whitespaces and comments occur wherever they are allowed in SQL-92 \citep{std:SQL1992}.
46 This Erratum updates the ADQL-2.0 recommandation removing the \xmlel{separator} token rule from the ADQL grammar \citep[BNF grammar, Appendix A, ]{std:ADQL} and, consequently, modifying the \xmlel{character\_string\_literal} to
47 \begin{lstlistings}[language=XML]
48 <character_string_literal> ::=
49 <quote> [ <character_representation>... ] <quote>
50 \end{lstlistings}
51 omitting the final
52 \begin{lstlistings}[language=sh]
53 [ { <separator>... <quote> [ <character_representation>... ] <quote> }... ]
54 \end{lstlistings}
55 These changes won't affect in any other way the ADQL grammar.
57 \section{Rationale}
58 The ADQL-2.0 recommendation lists in its Appendix A the BNF grammar for the SQL-like language. In this grammar a \xmlel{separator} is listed, with the following definition:
59 \begin{lstlistings}[language=sh]
60 <separator> ::= { <comment> | <space> | <newline> }...
61 \end{lstlistings}
62 However this nonterminal token is only referenced in the rule for the \xmlel{character\_string\_literal}, i.e.
63 \begin{lstlistings}[language=sh]
64 <character_string_literal> ::=
65 <quote> [ <character_representation>... ] <quote>
66 [ { <separator>... <quote> [ <character_representation>... ] <quote> }... ]
67 \end{lstlistings}
68 It is uncontentious that the intent is to allow comments and whitespace wherever SQL-92 allows them. The ADQL standard however says differently, and there should be a clarification.
69 Between to alternatives, adding a clarifying subsection to the ADQL-2.0 standard or removing the \xmlel{separator}, the second seems more attractive and has been considered suitable for a simple erratum to the current recommendation. The issue was in any case accepted as errata by the IVOA DAL WG at its first discussion.
71 \section{Impact Assessment}
72 The change introduced by this erratum has no other impact on the ADQL grammar and language apart from what already described in the previous sections of this note. Current implementations and parsers of ADQL query strings shouldn't be affacted at all by this change.
74 \appendix
75 \section{Changes from Previous Versions}
77 No previous versions yet.
78 % these would be subsections "Changes from v. WD-..."
79 % Use itemize environments.
81 \bibliography{ivoatex/ivoabib}
83 \end{document}


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