docs/rel_1_4/Guides/JSONGrammar.xml

   1 <?xml version="1.0" encoding="utf-8"?>
   2
   3 <article version="5.0" xmlns="http://docbook.org/ns/docbook"
   4         xmlns:xi="http://www.w3.org/2003/XInclude" xmlns:xlink="http://www.w3.org/1999/xlink">
   5
   6         <title>Grammar of JSON Queries</title>
   7
   8         <para>
   9                 <author>
  10                         <personname>
  11                                 <firstname>Scott</firstname>
  12                                 <surname>McKellar</surname>
  13                         </personname>
  14                         <affiliation>
  15                                 <orgname>Equinox Software, Inc.</orgname>
  16                         </affiliation>
  17                 </author>
  18         </para>
  19
  20         <sect1>
  21                 <title>Introduction</title>
  22                 <para> The format of this grammar approximates Extended Backus-Naur notation. However it is
  23                         intended as input to human beings, not to parser generators such as Lex or Yacc. Do not
  24                         expect formal rigor. Sometimes narrative text will explain things that are clumsy to
  25                         express in formal notation. More often, the text will restate or summarize the formal
  26                         productions. </para>
  27                 <para> Conventions: </para>
  28                 <orderedlist>
  29                         <listitem>
  30                                 <para>The grammar is a series of productions.</para>
  31                         </listitem>
  32                         <listitem>
  33                                 <para>A production consists of a name, followed by "::=", followed by a definition
  34                                         for the name. The name identifies a grammatical construct that can appear on the
  35                                         right side of another production.</para>
  36                         </listitem>
  37                         <listitem>
  38                                 <para>Literals (including punctuation) are enclosed in 'single quotes', or in
  39                                         "double quotes" if case is not significant.</para>
  40                         </listitem>
  41                         <listitem>
  42                                 <para>A single quotation mark within a literal is escaped with a preceding
  43                                         backslash: 'dog\'s tail'.</para>
  44                         </listitem>
  45                         <listitem>
  46                                 <para>If a construct can be defined more than one way, then the alternatives may
  47                                         appear in separate productions; or, they may appear in the same production,
  48                                         separated by pipe symbols ( | ). The choice between these representations is of only
  49                                         cosmetic significance.</para>
  50                         </listitem>
  51                         <listitem>
  52                                 <para>A construct enclosed within [square brackets] is optional.</para>
  53                         </listitem>
  54                         <listitem>
  55                                 <para>A construct enclosed within {curly braces} may be repeated zero or more
  56                                         times.</para>
  57                         </listitem>
  58                         <listitem>
  59                                 <para>JSON allows arbitrary white space between tokens. To avoid ugly clutter, this
  60                                         grammar ignores the optional white space. </para>
  61                         </listitem>
  62                         <listitem>
  63                                 <para>In many cases a production defines a JSON object, i.e. a list of name-value
  64                                         pairs, separated by commas. Since the order of these name/value pairs is not
  65                                         significant, the grammar will not try to show all the possible sequences. In
  66                                         general it will present the required pairs first, if any, followed by any
  67                                         optional elements.</para>
  68                         </listitem>
  69                 </orderedlist>
  70
  71                 <para> Since both EBNF and JSON use curly braces and square brackets, pay close attention to
  72                         whether these characters are in single quotes. If they're in single quotes, they are
  73                         literal elements of the JSON notation. Otherwise they are elements of the EBNF notation.
  74                 </para>
  75         </sect1>
  76
  77         <sect1>
  78                 <title>Primitives</title>
  79                 <para> We'll start by defining some primitives, to get them out of the way. They're mostly
  80                         just what you would expect. </para>
  81
  82                 <productionset>
  83                         <production xml:id="ebnf.string">
  84                                 <lhs> string </lhs>
  85                                 <rhs> '"' chars '"' </rhs>
  86                         </production>
  87
  88                         <production xml:id="ebnf.chars">
  89                                 <lhs> chars </lhs>
  90                                 <rhs> any valid sequence of UTF-8 characters, with certain special characters
  91                                         escaped according to JSON rules </rhs>
  92                         </production>
  93
  94                         <production xml:id="ebnf.int_literal">
  95                                 <lhs> integer_literal </lhs>
  96                                 <rhs> [ sign ] digit { digit } </rhs>
  97                         </production>
  98
  99                         <production xml:id="ebnf.sign">
 100                                 <lhs> sign </lhs>
 101                                 <rhs> '+' | '-' </rhs>
 102                         </production>
 103
 104                         <production xml:id="ebnf.digits">
 105                                 <lhs> digit </lhs>
 106                                 <rhs>digit = '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9'</rhs>
 107                         </production>
 108
 109                         <production xml:id="ebnf.int_string">
 110                                 <lhs> integer_string </lhs>
 111                                 <rhs> '"' integer_literal '"' </rhs>
 112                         </production>
 113
 114                         <production xml:id="ebnf.int">
 115                                 <lhs> integer </lhs>
 116                                 <rhs> integer_literal | integer_string </rhs>
 117                         </production>
 118
 119                         <production xml:id="ebnf.num">
 120                                 <lhs> number </lhs>
 121                                 <rhs> any valid character sequence that is numeric according to JSON rules </rhs>
 122                         </production>
 123
 124                 </productionset>
 125
 126                 <para> When json_query requires an integral value, it will usually accept a quoted string
 127                         and convert it to an integer by brute force – to zero if necessary. Likewise it may
 128                         truncate a floating point number to an integral value. Scientific notation will be
 129                         accepted but may not give the intended results. </para>
 130
 131                 <productionset>
 132
 133                         <production xml:id="ebnf.bool">
 134                                 <lhs> boolean </lhs>
 135                                 <rhs> 'true' | 'false' | string | number </rhs>
 136                         </production>
 137
 138                 </productionset>
 139
 140                 <para> The preferred way to encode a boolean is with the JSON reserved word true or false,
 141                         in lower case without quotation marks. The string <literal>true</literal>, in upper,
 142                         lower, or mixed case, is another way to encode true. Any other string evaluates to
 143                         false. </para>
 144                 <para> As an accommodation to perl, numbers may be used as booleans. A numeric value of 1
 145                         means true, and any other numeric value means false. </para>
 146                 <para> Any other valid JSON value, such as an array, will be accepted as a boolean but
 147                         interpreted as false. </para>
 148                 <para> The last couple of primitives aren't really very primitive, but we introduce them
 149                         here for convenience: </para>
 150
 151                 <productionset>
 152
 153                         <production xml:id="ebnf.classname">
 154                                 <lhs> class_name </lhs>
 155                                 <rhs> string </rhs>
 156                         </production>
 157
 158                 </productionset>
 159
 160                 <para> A class_name is a special case of a string: the name of a class as defined by the
 161                         IDL. The class may refer either to a database table or to a source_definition, which is
 162                         a subquery. </para>
 163
 164                 <productionset>
 165
 166                         <production xml:id="ebnf.field_name">
 167                                 <lhs> field_name </lhs>
 168                                 <rhs> string </rhs>
 169                         </production>
 170
 171                 </productionset>
 172
 173                 <para> A field_name is another special case of a string: the name of a non-virtual field as
 174                         defined by the IDL. A field_name is also a column name for the table corresponding to
 175                         the relevant class. </para>
 176
 177         </sect1>
 178
 179         <sect1>
 180                 <title>Query</title>
 181
 182                 <para> The following production applies not only to the main query but also to most
 183                         subqueries. </para>
 184
 185                 <productionset>
 186
 187                         <production xml:id="ebnf.query">
 188                                 <lhs> query </lhs>
 189                                 <rhs>
 190                                         '{'<sbr/>
 191                                         '"from"' ':' from_list<sbr/>
 192                                         [ ',' '"select"' ':' select_list ]<sbr/>
 193                                         [ ',' '"where"' ':' where_condition ]<sbr/>
 194                                         [ ',' '"having"' ':' where_condition ]<sbr/>
 195                                         [ ',' '"order_by"' ':' order_by_list ]<sbr/>
 196                                         [ ',' '"limit"' ':' integer ]<sbr/>
 197                                         [ ',' '"offset"' ':' integer ]<sbr/>
 198                                         [ ',' '"distinct"' ':' boolean ]<sbr/>
 199                                         [ ',' '"no_i18n"' ':' boolean ]<sbr/>
 200                                         '}'
 201                                 </rhs>
 202                         </production>
 203
 204                 </productionset>
 205
 206                 <para> Except for the <literal>"distinct"</literal> and <literal>no_i18n</literal> entries,
 207                         each name/value pair represents a major clause of the SELECT statement. The name/value
 208                         pairs may appear in any order. </para>
 209                 <para> There is no name/value pair for the GROUP BY clause, because json_query generates it
 210                         automatically according to information encoded elsewhere. </para>
 211                 <para> The <literal>"distinct"</literal> entry, if present and true, tells json_query that
 212                         it may have to create a GROUP BY clause. If not present, it defaults to false. </para>
 213                 <para> The <literal>"no_i18n"</literal> entry, if present and true, tells json_query to
 214                         suppress internationalization. If not present, it defaults to false. (Note that
 215                                 <literal>"no_i18n"</literal> contains the digit one, not the letter ell.) </para>
 216                 <para> The values for <literal>limit</literal> and <literal>offset</literal> provide the
 217                         arguments of the LIMIT and OFFSET clauses, respectively, of the SQL statement. Each
 218                         value should be non-negative, if present, or else the SQL won't work. </para>
 219
 220         </sect1>
 221
 222
 223 </article>