last_tab ="tab1";
function show(layerName) {
document.getElementById(layerName).style.display = "";
}

function hide(layerName) {
document.getElementById(layerName).style.display = "none";
}

function show_next(tab_name) {
document.getElementById(last_tab).className = "tab";
var curr = document.getElementById(tab_name);
curr.className="tab_hover";
hide(last_tab+"_data");
show(tab_name+"_data");
last_tab = tab_name;
}