public static function validate($data) {
        if ( ! is_array($data) ) return '$data must be an array';
        $id = U::get($data, 'id');
        if ( $id ) {
            if ( ! is_int($id) ) return "id must be an an integer";
        }
        $uk1 = U::get($data, 'uk1');
        if ( $uk1 ) {
            if ( ! is_string($uk1) ) return "uk1 must be a string";
            if ( strlen($uk1) < 1 || strlen($uk1) > 150 ) return "uk1 must be no more than 150 characters";
        }
        $sk1 = U::get($data, 'sk1');
        if ( $sk1 ) {
            if ( ! is_string($sk1) ) return "sk1 must be a string";
            if ( strlen($sk1) < 1 || strlen($sk1) > 75 ) return "sk1 must be no more than 75 characters";
        }
        $tk1 = U::get($data, 'tk1');
        if ( $tk1 ) {
            if ( ! is_string($tk1) ) return "tk1 must be a string";
            if ( strlen($tk1) < 1 ) return "tk1 cannot be empty";
        }
        $co1 = U::get($data, 'co1');
        if ( $co1 ) {
            if ( ! is_string($co1) ) return "co1 must be a string";
            if ( strlen($co1) < 1 || strlen($co1) > 150 ) return "co1 must be no more than 150 characters";
        }
        $co2 = U::get($data, 'co2');
        if ( $co2 ) {
            if ( ! is_string($co2) ) return "co2 must be a string";
            if ( strlen($co2) < 1 || strlen($co2) > 150 ) return "co2 must be no more than 150 characters";
        }
        return true;
    }