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+<?xml version="1.0" encoding="utf-8"?>
+
+<article version="5.0" xmlns="http://docbook.org/ns/docbook"
+ xmlns:xi="http://www.w3.org/2003/XInclude" xmlns:xlink="http://www.w3.org/1999/xlink">
+
+ <title>Grammar of JSON Queries</title>
+
+ <para>
+ <author>
+ <personname>
+ <firstname>Scott</firstname>
+ <surname>McKellar</surname>
+ </personname>
+ <affiliation>
+ <orgname>Equinox Software, Inc.</orgname>
+ </affiliation>
+ </author>
+ </para>
+
+ <sect1>
+ <title>Introduction</title>
+ <para> The format of this grammar approximates Extended Backus-Naur notation. However it is
+ intended as input to human beings, not to parser generators such as Lex or Yacc. Do not
+ expect formal rigor. Sometimes narrative text will explain things that are clumsy to
+ express in formal notation. More often, the text will restate or summarize the formal
+ productions. </para>
+ <para> Conventions: </para>
+ <orderedlist>
+ <listitem>
+ <para>The grammar is a series of productions.</para>
+ </listitem>
+ <listitem>
+ <para>A production consists of a name, followed by "::=", followed by a definition
+ for the name. The name identifies a grammatical construct that can appear on the
+ right side of another production.</para>
+ </listitem>
+ <listitem>
+ <para>Literals (including punctuation) are enclosed in 'single quotes', or in
+ "double quotes" if case is not significant.</para>
+ </listitem>
+ <listitem>
+ <para>A single quotation mark within a literal is escaped with a preceding
+ backslash: 'dog\'s tail'.</para>
+ </listitem>
+ <listitem>
+ <para>If a construct can be defined more than one way, then the alternatives may
+ appear in separate productions; or, they may appear in the same production,
+ separated by pipe symbols. The choice between these representations is of only
+ cosmetic significance.</para>
+ </listitem>
+ <listitem>
+ <para>A construct enclosed within square brackets is optional.</para>
+ </listitem>
+ <listitem>
+ <para>A construct enclosed within curly braces may be repeated zero or more
+ times.</para>
+ </listitem>
+ <listitem>
+ <para>JSON allows arbitrary white space between tokens. To avoid ugly clutter, this
+ grammar ignores the optional white space. </para>
+ </listitem>
+ <listitem>
+ <para>In many cases a production defines a JSON object, i.e. a list of name-value
+ pairs, separated by commas. Since the order of these name/value pairs is not
+ significant, the grammar will not try to show all the possible sequences. In
+ general it will present the required pairs first, if any, followed by any
+ optional elements.</para>
+ </listitem>
+ </orderedlist>
+
+ <para> Since both EBNF and JSON use curly braces and square brackets, pay close attention to
+ whether these characters are in single quotes. If they're in single quotes, they are
+ literal elements of the JSON notation. Otherwise they are elements of the EBNF notation.
+ </para>
+ </sect1>
+
+ <sect1>
+ <title>Primitives</title>
+ <para> We'll start by defining some primitives, to get them out of the way. They're mostly
+ just what you would expect. </para>
+
+ <productionset>
+ <production xml:id="ebnf.string">
+ <lhs> string </lhs>
+ <rhs> '"' chars '"' </rhs>
+ </production>
+
+ <production xml:id="ebnf.chars">
+ <lhs> chars </lhs>
+ <rhs> any valid sequence of UTF-8 characters, with certain special characters
+ escaped according to JSON rules </rhs>
+ </production>
+
+ <production xml:id="ebnf.int_literal">
+ <lhs> integer_literal </lhs>
+ <rhs> [ sign ] digit { digit } </rhs>
+ </production>
+
+ <production xml:id="ebnf.sign">
+ <lhs> sign </lhs>
+ <rhs> '+' | '-' </rhs>
+ </production>
+
+ <production xml:id="ebnf.digits">
+ <lhs> digit </lhs>
+ <rhs>digit = '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9'</rhs>
+ </production>
+
+ <production xml:id="ebnf.int_string">
+ <lhs> integer_string </lhs>
+ <rhs> '"' integer_literal '"' </rhs>
+ </production>
+
+ <production xml:id="ebnf.int">
+ <lhs> integer </lhs>
+ <rhs> integer_literal | integer_string </rhs>
+ </production>
+
+ <production xml:id="ebnf.num">
+ <lhs> number </lhs>
+ <rhs> any valid character sequence that is numeric according to JSON rules </rhs>
+ </production>
+
+ </productionset>
+
+ <para> When json_query requires an integral value, it will usually accept a quoted string
+ and convert it to an integer by brute force – to zero if necessary. Likewise it may
+ truncate a floating point number to an integral value. Scientific notation will be
+ accepted but may not give the intended results. </para>
+
+ <productionset>
+
+ <production xml:id="ebnf.bool">
+ <lhs> boolean </lhs>
+ <rhs> 'true' | 'false' | string | number </rhs>
+ </production>
+
+ </productionset>
+
+ <para> The preferred way to encode a boolean is with the JSON reserved word true or false,
+ in lower case without quotation marks. The string <literal>true</literal>, in upper,
+ lower, or mixed case, is another way to encode true. Any other string evaluates to
+ false. </para>
+ <para> As an accommodation to perl, numbers may be used as booleans. A numeric value of 1
+ means true, and any other numeric value means false. </para>
+ <para> Any other valid JSON value, such as an array, will be accepted as a boolean but
+ interpreted as false. </para>
+ <para> The last couple of primitives aren't really very primitive, but we introduce them
+ here for convenience: </para>
+
+ <productionset>
+
+ <production xml:id="ebnf.classname">
+ <lhs> class_name </lhs>
+ <rhs> string </rhs>
+ </production>
+
+ </productionset>
+
+ <para> A class_name is a special case of a string: the name of a class as defined by the
+ IDL. The class may refer either to a database table or to a source_definition, which is
+ a subquery. </para>
+
+ <productionset>
+
+ <production xml:id="ebnf.field_name">
+ <lhs> field_name </lhs>
+ <rhs> string </rhs>
+ </production>
+
+ </productionset>
+
+ <para> A field_name is another special case of a string: the name of a non-virtual field as
+ defined by the IDL. A field_name is also a column name for the table corresponding to
+ the relevant class. </para>
+
+ </sect1>
+
+ <sect1>
+ <title>Query</title>
+
+ <para> The following production applies not only to the main query but also to most
+ subqueries. </para>
+
+ <productionset>
+
+ <production xml:id="ebnf.query">
+ <lhs> query </lhs>
+ <rhs> '{'<sbr/> '"from"' ':' from_list<sbr/> [ ',' '"select"' ':' select_list
+ ]<sbr/> [ ',' '"where"' ':' where_condition ]<sbr/> [ ',' '"having"' ':'
+ where_condition ]<sbr/> [ ',' '"order_by"' ':' order_by_list ]<sbr/> [ ','
+ '"limit"' ':' integer ]<sbr/> [ ',' '"offset"' ':' integer ]<sbr/> [ ','
+ '"distinct"' ':' boolean ]<sbr/> [ ',' '"no_i18n"' ':' boolean ]<sbr/> '}'
+ </rhs>
+ </production>
+
+ </productionset>
+
+ <para> Except for the <literal>"distinct"</literal> and <literal>no_i18n</literal> entries,
+ each name/value pair represents a major clause of the SELECT statement. The name/value
+ pairs may appear in any order. </para>
+ <para> There is no name/value pair for the GROUP BY clause, because json_query generates it
+ automatically according to information encoded elsewhere. </para>
+ <para> The <literal>"distinct"</literal> entry, if present and true, tells json_query that
+ it may have to create a GROUP BY clause. If not present, it defaults to false. </para>
+ <para> The <literal>"no_i18n"</literal> entry, if present and true, tells json_query to
+ suppress internationalization. If not present, it defaults to false. (Note that
+ <literal>"no_i18n"</literal> contains the digit one, not the letter ell.) </para>
+ <para> The values for <literal>limit</literal> and <literal>offset</literal> provide the
+ arguments of the LIMIT and OFFSET clauses, respectively, of the SQL statement. Each
+ value should be non-negative, if present, or else the SQL won't work. </para>
+
+ </sect1>
+
+
+</article>
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