<?php
    class Conexao {
        public $conn;
        function Conexao() {
            $string  = "mysql:";
            $string .= "host=localhost ";
            $string .= "port=5432 ";
            $string .= "dbname=nomedobanco";
            $string .= "user=usuario";
            $string .= "password=senha";

            try {
                $this->conn = new PDO($string);
            }catch(PDOException $e){
                echo $e->getMessage();
            }

        }

    }





?>

new PDO('mysql:host=localhost;dbname=testdb;charset=utf8mb4', 'username', 'password');

<?php

    require('class.conexao.php');

    class Querys extends Conexao {


        function validaLogin($login, $senha) {

            $sql =
                    "
                        select nome, cpf from validaUsuario('".$login."', '".$senha."');
                    ";

            $stmt = $this->conn->prepare($sql);
            $stmt->execute();
            $result = $stmt->fetchAll(PDO::FETCH_ASSOC);
            return $result;

        }


}

$stmt = $this->conn->prepare($sql);
        $stmt->execute();
        $result = $stmt->fetchAll(PDO::FETCH_ASSOC);
        return $result;

<?php
    require_once('class.querys.php');

    class Editora extends Querys {

        function listaEditora() {

                $query = new Querys();

                $retorno = $query->validaLogin(aqui vem os parametros));

                return $retorno;
        }
    }

?>