RRDiagram

Generate railroad diagrams from code or BNF. Generate BNF from code.

RR Diagram is a Java library that generates railroad diagrams (also called syntax diagrams) from code or from BNF notation. The output format is a very compact SVG image which can be integrated to web pages and where rules can contain links.

RR Diagram can also be used to generate BNF notation from a model.

The generated output was inspired from this online-only version: http://railroad.my28msec.com/rr/ui

Binaries can be found on the SourceForge page.

Example

This is the kind of diagrams that can get generated:

The above is generated using the right conversion options on this BNF:

H2_SELECT = 
'SELECT' [ 'TOP' term ] [ 'DISTINCT' | 'ALL' ] selectExpression {',' selectExpression} \
'FROM' tableExpression {',' tableExpression} [ 'WHERE' expression ] \
[ 'GROUP BY' expression {',' expression} ] [ 'HAVING' expression ] \
[ ( 'UNION' [ 'ALL' ] | 'MINUS' | 'EXCEPT' | 'INTERSECT' ) select ] [ 'ORDER BY' order {',' order} ] \
[ 'LIMIT' expression [ 'OFFSET' expression ] [ 'SAMPLE_SIZE' rowCountInt ] ] \
[ 'FOR UPDATE' ];

Usage

The diagram model represents the actual constructs visible on the diagram. To convert a diagram model to SVG:

RRDiagram rrDiagram = new RRDiagram(rrElement);
RRDiagramToSVG rrDiagramToSVG = new RRDiagramToSVG();
String svg = rrDiagramToSVG.convert(rrDiagram);

The grammar model represents a BNF-like grammar. It can be converted to a diagram model:

Grammar grammar = new Grammar(rules);
GrammarToRRDiagram grammarToRRDiagram = new GrammarToRRDiagram();
for(Rule rule: grammar.getRules()) {
  RRDiagram rrDiagram = grammarToRRDiagram.convert(rule);
  // Do something with diagram, like get the SVG.
}

The grammar model can be created from code, or can read BNF syntax:

BNFToGrammar bnfToGrammar = new BNFToGrammar();
Grammar grammar = bnfToGrammar.convert(reader);
// Do something with grammar, like get the diagram for SVG output.

The grammar model can also be saved to BNF syntax:

GrammarToBNF grammarToBNF = new GrammarToBNF();
// Set options on the grammarToBNF object
String bnf = grammarToBNF.convert(grammar);

BNF Syntax

The supported BNF subset when reading is the following:

- definition
    =
    :=
    ::=
- concatenation
    ,
    <whitespace>
- termination
    ;
- alternation
    |
- option
    [ ... ]
    ?
- repetition
    { ... } => 0..N
    expression* => 0..N
    expression+ => 1..N
    <digits> * expression => <digits>...<digits>
    <digits> * [expression] => <0>...<digits>
    <digits> * expression? => <0>...<digits>
- grouping
    ( ... )
- literal
    " ... " or ' ... '
- special characters
    (? ... ?)
- comments
    (* ... *)

When getting the BNF syntax from the grammar model, it is possible to tweak the kind of BNF to get by changing some options on the converter.

License

This library is provided under the ASL 2.0.