Description

A productionset is a collection of Extended Backus-Naur Form (EBNF) productions.

EBNF is a notation for describing the grammar of context-free languages. Even if you aren’t conversant in the programming language concepts of context-free languages and grammars, it’s not really as hard to understand as it sounds.

See Also

constraint, lhs, production, productionrecap, rhs

Examples

A set of EBNF productions describes the legal arrangements of tokens in a language. Consider arithmetic expressions as a simple example.

The expression 3 + 4 is valid and so is 3 + 4 - 5, but 3 - + - 4 is not, nor is 3 + 4 6. We can use EBNF to describe all the possible legal arrangements.

That is expressed in DocBook like this:

<article xmlns='http://docbook.org/ns/docbook'>
<title>Example productionset</title>

<simplesect><title>EBNF Grammar</title>

<productionset><title>Arithemetic Expressions</title>
<production xml:id="ebnf.expression">
  <lhs>Expression</lhs>
  <rhs><nonterminal def="#ebnf.arith">ArithExpression</nonterminal> |
       <nonterminal def="#ebnf.mult">MultExpression</nonterminal>
  <lineannotation>Does this grammar actually get precedence right?
  </lineannotation>
  </rhs>
</production>
<production xml:id="ebnf.arith">
  <lhs>ArithExpression</lhs>
  <rhs><nonterminal def="#ebnf.expression">Expression</nonterminal>
       '+'
       <nonterminal def="#ebnf.mult">MultExpression</nonterminal> |
       <nonterminal def="#ebnf.expression">Expression</nonterminal>
       '-'
       <nonterminal def="#ebnf.mult">MultExpression</nonterminal>
  </rhs>
</production>
<production xml:id="ebnf.mult">
  <lhs>MultExpression</lhs>
  <rhs><nonterminal def="#ebnf.mult">MultExpression</nonterminal>
       '*'
       <nonterminal def="#ebnf.mult">MultExpression</nonterminal> |
       <nonterminal def="#ebnf.mult">MultExpression</nonterminal>
       '/'
       <nonterminal def="#ebnf.mult">MultExpression</nonterminal> |
       <nonterminal def="#ebnf.number">Number</nonterminal>
  </rhs>
  <constraint linkend="div0"/>
</production>
<production xml:id="ebnf.number">
  <lhs>Number</lhs>
  <rhs>[0-9]+</rhs>
</production>
</productionset>

<constraintdef xml:id="div0">
<title>Division by Zero</title>
<para>Division by zero is an error.</para>
</constraintdef>
</simplesect>

</article>