function ColumnsObj() {
    
    this.addNew = function(id,ctype) {
    // append column object to the array 'app.catArr' with the parameters above
    // (.ID,.Title,.HTML,.Show).
    //
    // return: nothing.
        
        app.catArr[id] = {
            ID : id,
            Title : ctype,
            HTML : "<div class=\"cat_main\" id=\"cat_main_"+id+"\">\n"
                +"<div id=\"cat_"+id+"_title\" class=\"cat_title\" style=\"\">"+ctype+"</div>\n"
                +"<div height=\"300\" id=\"cat_"+id+"_content\" class=\"cat_content\" style=\"\"></div>\n"
                +"<div id=\"cat_"+id+"_bottom\" class=\"cat_foot\" style=\"\"></div></div>\n"
            ,
            Show : false
        }
    }
    
    this.showCat = function() {
    // synchronize the category objects with the view specials objects, by
    // changing the show status (true/false) of relevant category objects
    // and print into html the categories.
    //
    // return: number of categories showed.
        
        for (i=0; i<app.catArr.length; i++)
            app.catArr[i].Show = false;
        for (i=0; i<app.viewArr.length; i++)
            app.catArr[app.viewArr[i].CatID].Show = true;
        
        co = 0;
        for (i=0; i<app.catArr.length; i++)
            if (app.catArr[i].Show) {
                $('#specials_main').append(app.catArr[i].HTML); //print into html
                co++
            }
        return co;
    }
}