/rdfapi-php/api/syntax/N3Serializer.php

<?php

// ----------------------------------------------------------------------------------
// Class: N3Serializer
// ----------------------------------------------------------------------------------

/**
 * PHP Notation3 Serializer
 *
 * This class serialises models to N3 Syntax.
 *
 * Supported N3 features:
 * <ul>
 *   <li>Using [ ] for blank nodes, or _: if necessary</li>
 *   <li>Literal datatype- and xmlLanguageTag support</li>
 * </ul>
 *
 * Un-supported N3 Features include:
 * <ul>
 *   <li>Reification</li>
 * </ul>
 *
 *
 * @author Gunnar AA. Grimnes <ggrimnes@csd.abdn.ac.uk>
 * @author Daniel Westphal <mail@d-westphal.de>
 * @author Christian Weiske <cweiske@cweiske.de>
 * @version $Id: N3Serializer.php 556 2008-01-22 10:52:48Z fusel2k $
 * @package syntax
 * @access public
 **/

define('MAGIC_STRING', '~~~');

class N3Serializer extends Object
{

    var $debug = false;

    var $prefixes   = array();
    var $noPrefixes = array();

    var $done;  // keeps track of already serialized resources
    var $resourcetext;
    var $resourcetext_taken;
    var $model;
    var $res;
    var $anon;

    var $styleCompress = false;
    var $stylePretty   = false;
    var $styleNest     = false;

    /**
    * Constructor
    *
    * @access   public
    */
    function N3Serializer()
    {
        $this->debug = false;
    }


    /**
    * Adds a new namespace prefix to use.
    * Unknown namespaces will become ns0, ns1 etc.
    * @access public
    * @param string $s
    * @returns void
    **/
    function addNSPrefix($ns, $prefix)
    {
        $this->prefixes[$ns] = $prefix;
    }



    /**
    * Clears all previously set namespace prefixes
    */
    function clearNSPrefixes()
    {
        $this->prefixes = array();
    }



    /**
    *   Add a namespace that shall not get shortened by using a prefix.
    *
    *   @param string $ns Namespace URI like "http://example.com/"
    */
    function addNoNSPrefix($ns)
    {
        $this->noPrefixes[$ns] = true;
    }



    /**
    * Clears all previously set noNamespace prefixes
    */
    function clearNoNSPrefixes()
    {
        $this->noPrefixes = array();
    }



    /**
    * Serializes a model to N3 syntax.
    *
    * @param     object Model $model
    * @return    string
    * @access    public
    */
    function &serialize(&$m)
    {
        if (is_a($m, 'DbModel')) {
            $m=$m->getMemModel();
        }

        $this->reset();
        $this->model = $m;
        $this->res   = "";

        // copy default namespaces
        global $default_prefixes;
        foreach($default_prefixes as $prefix => $namespace) {
            $this->addNSPrefix($namespace,$prefix);
        }

        $nps= $this->model->getParsedNamespaces();
        if ($nps!=false) {
            foreach ($nps as $uri => $prefix){
                $this->addNSPrefix($uri,$prefix);
            }
        }

        $namespaces = array();
        $count      = array();
        $resources  = array();
        foreach ($this->model->triples as $t) {
            $s = $t->getSubject();
            if (is_a($s, 'Resource')) {
                $namespaces[$s->getNamespace()] = 1;
            }
            $p = $t->getPredicate();
            if (is_a($p, 'Resource')) {
                $namespaces[$p->getNamespace()] = 1;
            }
            $o = $t->getObject();
            if (is_a($o, 'Resource')) {
                $namespaces[$o->getNamespace()] = 1;
            }
            $uri = $s->getURI();

            if (isset($count[$uri])) {
                $count[$uri]++;
            } else {
                $count[$uri]     = 0;
                $resources[$uri] = $s;
            }

            if ($this->styleNest && is_a($s, 'BlankNode')) {
                //make sure blank nodes are sorted *after* normal nodes
                //so that they can be included
                $count[$uri] -= 0.00001;
            }
        }

        if (!HIDE_ADVERTISE) {
            $this->res .= '# Generated by N3Serializer.php from RDF RAP.'.LINEFEED
                        .'# http://www.wiwiss.fu-berlin.de/suhl/bizer/rdfapi/index.html'
                        .LINEFEED.LINEFEED;
        }

        $this->doNamespaces($namespaces);

        $this->res .= LINEFEED.LINEFEED;

        arsort($count);

        foreach ( $count as $k => $v) {
            $this->doResource($resources[$k]);
            //      $this->res.=" .\n";
        }

        //make all replacements
        do {
            $bReplacements = false;
            foreach ($this->resourcetext as $r => $t) {
                if (preg_match_all('/'.MAGIC_STRING.'([^ ]+)'.MAGIC_STRING.'/', $t, $ms, PREG_SET_ORDER)) {
                    foreach ($ms as $mseach) {
                        $rp = $this->resourcetext[$mseach[1]];
                        $this->resourcetext[$r] = preg_replace('/'.MAGIC_STRING.$mseach[1].MAGIC_STRING.'/', $rp, $t);
                        $bReplacements = true;
                    }
                }

            }
        } while ($bReplacements);

        //after all replacements took place, put the lines out
        $c = 0;
        foreach ($this->resourcetext as $r => $t) {
            if ($this->debug) {
                $this->res .= $c . ': ';
            }
            if (!(isset($this->resourcetext_taken[$r]) && $this->resourcetext_taken[$r]>0)) {
                $this->res .= $t . ' .' . LINEFEED;
                if ($this->stylePretty) {
                    $this->res .= LINEFEED;
                }
            } else if ($this->debug ) {
                $this->res.=' Skipping : '.$t.LINEFEED;
            }
            $c++;
        }

    //     $max=-1111;
    //     $maxkey="";
    //     foreach ($count as $k=>$c) {
    //       if ( $c>$max) { $maxkey=$k; $max=$c; }
    //     }

    //     if ($this->debug) {
    //       print "$maxkey is subject of most triples! ($max) \n";
    //     }

        return $this->res;
    }//function &serialize(&$m)



    /**
    * Serializes a model and saves it into a file.
    * Returns FALSE if the model couldn't be saved to the file.
    *
    * @param     object MemModel $model
    * @param     string $filename
    * @return    boolean
    * @access    public
    */
    function saveAs(&$model, $filename)
    {
        // serialize model
        $n3 = $this->serialize($model);

        // write serialized model to file
        $file_handle = @fopen($filename, 'w');
        if ($file_handle) {
            fwrite($file_handle, $n3);
            fclose($file_handle);
            return true;
        } else {
            return false;
        };
    }



    /**
    * Set to true, if the N3 serializer should try to compress the blank node
    *  syntax using [] whereever possible.
    */
    function setCompress($compress)
    {
        $this->styleCompress = $compress;
    }



    /**
    * Enables pretty printing in semicolon delimited sentences.
    */
    function setPrettyPrint($prettyPrint)
    {
        $this->stylePretty = $prettyPrint;
    }



    /**
    * Enables nesting of blank nodes with [] if
    * compression is activated via @see setCompress
    */
    function setNest($nest)
    {
        $this->styleNest = $nest;
    }

  /* ==================== Private Methods from here ==================== */


    /**
    * Readies this object for serializing another model
    * @access private
    * @param void
    * @returns void
    **/
    function reset()
    {
        $this->anon               = 0;
        $this->done               = array();
        $this->resourcetext_taken = array();
        $this->resourcetext       = array();
        $this->res                = '';
        $this->model              = null;
    }



    /**
    * Makes ns0, ns1 etc. prefixes for unknown prefixes.
    * Outputs @prefix lines.
    * @access private
    * @param array $n
    * @returns void
    **/
    function doNamespaces(&$n)
    {
        $c = 0;
        foreach ($n as $ns => $nonsense) {
            if (!$ns || isset($this->noPrefixes[$ns])) {
                continue;
            }
            if (isset($this->prefixes[$ns])) {
                $p = $this->prefixes[$ns];
            } else {
                $p = 'ns' . $c;
                $this->prefixes[$ns] = $p;
                $c++;
            }
            $this->res .= "@prefix $p: <".$ns.'> .'.LINEFEED;
        }
    }



    /**
    * Fill in $resourcetext for a single resource.
    * Will recurse into Objects of triples, but should never look ? (really?)
    * @param object Resource $r
    * @returns boolean
    * @access private
    **/
    function doResource(&$r, $bEmbedded = false, $strIndent = '    ')
    {
        //var_dump($r->getURI());

        $ts = $this->model->find($r, null, null);
        if (count($ts->triples) == 0) {
            if ($bEmbedded) {
                $this->resourcetext[$r->getURI()] = '_:' . $r->getLabel();
            }
            return;
        }

        $out = '';

        if (isset($this->done[$r->getURI()]) && $this->done[$r->getURI()]) {
            if (!$this->styleNest && is_a($r, 'BlankNode')) {
                if ($this->resourcetext_taken[$r->getURI()] == 1) {
                    //Oh bother, we must use the _:blah construct.
                    $a = $this->resourcetext[$r->getURI()];
                    $this->resourcetext[$r->getURI()]='_:anon'.$this->anon;
                    $this->resourcetext['_:anon'.$this->anon]=$this->fixAnon($a, '_:anon'.$this->anon);
                    $this->resourcetext_taken[$r->getURI()]=2;
                    $this->anon++;
                }
            }
            return false;
        }

        $this->done[$r->getURI()] = true;
        $compress = false;

        if (is_a($r, 'Resource')) {
            if (is_a($r, 'BlankNode')) {
                //test if this blanknode is referenced somewhere
                $rbn      = $this->model->find(null, null, $r);
                $compress = (N3SER_BNODE_SHORT || $this->styleCompress)
                            && (
                                count($rbn->triples) == 0
                                || (count($rbn->triples) == 1 && $bEmbedded)
                            );
                if ($compress) {
                    $out.='[';
                } else {
                    $out.='_:'.$r->getLabel();
                }
            } else {
                $this->doURI($r, $out);
            }
        }

        usort($ts->triples, 'statementsorter');
        $lastp = '';
        $out  .= ' ';

        foreach ($ts->triples as $t) {
            $p = $t->getPredicate();

            if ($p === $lastp) {
                $out .= ' , ';
            } else {
                if ($lastp!='') {
                    if ($this->stylePretty) {
                        $out .= ";\n" . $strIndent;
                    } else {
                        $out .= ' ; ';
                    }
                }
                $this->doURI($p, $out);
                $lastp = $p;
            }

            $out .= ' ';

            $o = $t->getObject();

            if (is_a($o, 'Literal')) {
                $l = $o->getLabel();
                if (strpos($l, LINEFEED) === false) {
                    $long = false;
                } else {
                    $long = true;
                }

                //try to be intelligent
                $quoteSingle = strpos($l, '\'') !== false;
                $quoteDouble = strpos($l, '"')  !== false;
                if ($quoteSingle && !$quoteDouble) {
                    $quoteChar = $long ? '"""' : '"';
                } else if ($quoteDouble && !$quoteSingle) {
                    $quoteChar = $long ? '\'\'\'' : '\'';
                } else if ($quoteDouble && $quoteSingle) {
                    //both quotation chars inside
                    $quoteChar = $long ? '"""' : '"';
                    $l = addslashes($l);
                } else {
                    //no quotation chars
                    $quoteChar = $long ? '"""' : '"';
                }
                $out .= $quoteChar . $l . $quoteChar;

                if ( $o->getLanguage()!='' ) {
                    $out.='@'.$o->getLanguage();
                }
                if ( $o->getDatatype()!='' ) {
                    $out.='^^<'.$o->getDatatype().'>';
                }
            }

            if (is_a($o, 'Resource')) {
                if ($this->debug) {
                    print 'Doing object: '.$o->getURI().LINEFEED;
                }
                if (is_a($o, 'BlankNode')) {
                    if ($this->styleNest && $this->styleCompress
                     && !isset($this->done[$o->getURI()])
                    ) {
                        $this->doResource($o, true, $strIndent . '    ');
                        $out .= MAGIC_STRING . $o->getURI() . MAGIC_STRING;
                        //$out .= $this->resourcetext[$o->getURI()];
                        $this->resourcetext_taken[$o->getURI()] = 1;
                    } else {
                        $out .= '_:'.$o->getLabel();
                    }
                } else {
                    $this->doURI($o, $out);
                }
            }
        }

        if ($compress) {
            $out .= ' ]';
        };

        $this->resourcetext[$r->getURI()]=$out;

        return true;
    }//function doResource(&$r)



    /**
    * Format a single URI
    * @param string $s
    * @return void
    * @access private
    **/
    function doURI(&$r, &$out)
    {
        if ($r->getURI() == 'http://www.w3.org/1999/02/22-rdf-syntax-ns#type') {
            $out .= 'a';
            return;
        }
        $ns = $r->getNamespace();
        if ($ns != '' && !isset($this->noPrefixes[$ns])) {
            $out .= $this->prefixes[$ns].':'.$r->getLocalName();
        } else {
            //Will this ever happen? It does, now.
            $out .= '<' . $r->getURI() . '>';
        }
    }



    /**
    * Fix the resourcetext for a blanknode where the _: construct was used
    * @param string $s
    * @param string $a
    * @access private
    * @return void
    **/
    function fixAnon($t,$a)
    {
        $t = preg_replace("/( \] $|^\[ )/", '', $t);
        return $a . $t;
    }

}

?>