// global xmlhttprequest object
    var xmlHttp = false;
    var sSection = "";
    var value;
        
    /** AJAX functions **/
    
    // constants
    var REQUEST_GET     = 0;
    var REQEST_POST     = 2;
    var REQUEST_HEAD    = 1;
    var REQUEST_XML     = 3;
    
    /**
     * instantiates a new xmlhttprequest object
     *
     * @return xmlhttprequest object or false
     */
    function getXMLRequester( )
    {
        var xmlHttp = false;
                
        // try to create a new instance of the xmlhttprequest object        
        try
        {
            // Internet Explorer
            if( window.ActiveXObject )
            {
                for( var i = 5; i; i-- )
                {
                    try
                    {
                        // loading of a newer version of msxml dll (msxml3 - msxml5) failed
                        // use fallback solution
                        // old style msxml version independent, deprecated
                        if( i == 2 )
                        {
                            xmlHttp = new ActiveXObject( "Microsoft.XMLHTTP" );    
                        }
                        // try to use the latest msxml dll
                        else
                        {
                            
                            xmlHttp = new ActiveXObject( "Msxml2.XMLHTTP." + i + ".0" );
                        }
                        break;
                    }
                    catch( excNotLoadable )
                    {                        
                        xmlHttp = false;
                    }
                }
            }
            // Mozilla, Opera und Safari
            else if( window.XMLHttpRequest )
            {
                xmlHttp = new XMLHttpRequest();
                if (xmlHttp.overrideMimeType) {
                  xmlHttp.overrideMimeType('text/html; charset=ISO-8859-1');
               }
            }
        }
        // loading of xmlhttp object failed
        catch( excNotLoadable )
        {
            xmlHttp = false;
        }
        return xmlHttp ;
    }
    
    
    /**
     * sends a http request to server
     *
     * @param strSource, String, datasource on server, e.g. data.php
     *
     * @param strData, String, data to send to server, optionally
     *
     * @param intType, Integer,request type, possible values: REQUEST_GET, REQUEST_POST, REQUEST_XML, REQUEST_HEAD default REQUEST_GET
     *
     * @param strData, Integer, ID of this request, will be given to registered event handler onreadystatechange', optionally
     *
     * @return String, request data or data source
     */
    function sendRequest( strSource, strData, intType, intID )
    {
        if( !strData )
            strData = '';
    
        // default type (0 = GET, 1 = xml, 2 = POST )
        if( isNaN( intType ) )
            intType = 0; // GET
    
        // previous request not finished yet, abort it before sending a new request
        if( xmlHttp && xmlHttp.readyState )
        {
            xmlHttp.abort( );
            xmlHttp = false;
        }
            
        // create a new instance of xmlhttprequest object
        // if it fails, return
        if( !xmlHttp )
        {
            xmlHttp = getXMLRequester( );
            if( !xmlHttp )
                return;
        }
        
        // parse query string
        if( intType != 1 && ( strData && strData.substr( 0, 1 ) == '&' || strData.substr( 0, 1 ) == '?' ) )
            strData = strData.substring( 1, strData.length );

        // data to send using POST
        var dataReturn = strData ? strData : strSource;
        
        switch( intType )
        {
            case 1:    // xml
                strData = "xml=" + strData;
            case 2: // POST
                // open the connection 
                xmlHttp.open( "POST", strSource, true );
                xmlHttp.setRequestHeader( 'Content-Type', 'application/x-www-form-urlencoded' );
                xmlHttp.setRequestHeader( 'Content-length', strData.length );
                break;
            case 3: // HEAD
                // open the connection 
                xmlHttp.open( "HEAD", strSource, true );
                strData = null;
                break;
            default: // GET
                // open the connection 
                var strDataFile = strSource + (strData ? '?' + strData : '' );
                xmlHttp.open( "GET", strDataFile, true );
                strData = null;
        }
        
        // set onload data event-handler
        xmlHttp.onreadystatechange = new Function( "", "processResponse(" + intID + ")" ); ;

        // send request to server
        xmlHttp.send( strData );    // param = POST data
        
        return dataReturn;
    }
        
    
    /**
     * process the response data from server
     *
     * @param intID, Integer, ID of this response
     */
    function processResponse( intID )
    {
        // status 0 UNINITIALIZED open() has not been called yet.
        // status 1 LOADING send() has not been called yet.
        // status 2 LOADED send() has been called, headers and status are available.
        // status 3 INTERACTIVE Downloading, responseText holds the partial data.
        // status 4 COMPLETED Finished with all operations.
        switch( xmlHttp.readyState ) {
            // uninitialized
            case 0:
            // loading
            case 1:
            // loaded
            case 2:
            // interactive
            case 3:
                break;
            // complete
            case 4:    
                // check http status
                // success
                if( xmlHttp.status == 200 ) {   
                    processData( xmlHttp, intID );

                // loading not successfull, e.g. page not available
        		}else{		
                    if( window.handleAJAXError ) {
                        handleAJAXError( xmlHttp, intID );
        			}else{
                     	// alert( "ERROR\n HTTP status = " + xmlHttp.status + "\n" + xmlHttp.statusText ) ;
        			}
                }
            break;
        }
    }

    
    /** real application functions **/
    
    
    // process data from server
    function processData( xmlHttp, intID )
    {
        // alert( xmlHttp.responseText ); 
        // process text data
        switch( sSection ) {
            case 'start':
                document.getElementById("select1").innerHTML = xmlHttp.responseText;
            break;
            case 'hersteller':
                document.getElementById('select6').style.visibility = 'visible';
                document.getElementById("select6").innerHTML = '<img src="/logo/'+value+'/Logo.jpg">';
                document.getElementById("select2").innerHTML = xmlHttp.responseText;
                document.getElementById("select3").innerHTML = '';
                document.getElementById("select4").innerHTML = '';
            break;
            case 'modell':
                document.getElementById("select3").innerHTML = xmlHttp.responseText; 
                document.getElementById("select4").innerHTML = '';
            break;
            case 'austattung':
                document.getElementById('seldiv4').style.visibility = 'visible';
                document.getElementById("select4").innerHTML = xmlHttp.responseText; 
            break;
            case 'autos':
                // document.getElementById("select5").innerHTML = xmlHttp.responseText; 
            break;
            
        }
        // updateMenu( xmlHttp.responseText );
    }
    
    
    function getData() { 
        
        var sOpt;
        switch( sSection ) {
            case 'start':
                sOpt = '/search.php?start=1'; 
            break;
            case 'hersteller':
                sOpt = '/search.php?hersteller_id='; 
            break;
            case 'modell':
                sOpt = '/search.php?modell_id=';
            break;
            case 'austattung':
                sOpt = '/search.php?austattung_id=';
            break;
            case 'autos':
                sOpt = '/search.php?aid=';
            break;
        }   
        
        var strURL = sOpt + value + "";
        
        sendRequest( strURL );
    }
    
    function ajaxStart() {
        sSection = 'start'; 
        getData()
    }