logback iniciar sesión en Oracle provoca un error de dialecto

<appender name="db-classic-oracle" class="ch.qos.logback.classic.db.DBAppender">  
        <connectionSource class="ch.qos.logback.core.db.DriverManagerConnectionSource">  
            <dataSource class="com.mchange.v2.c3p0.ComboPooledDataSource">             	
                <driverClass>oracle.jdbc.driver.OracleDriver</driverClass>  
                <url>jdbc:oracle:thin:@localhost:1521:ZYD</url>  
                <user>scott</user>  
                <password>tiger</password>
                <sqlDialect class="ch.qos.logback.core.db.dialect.OracleDialect" />   
            </dataSource>  
        </connectionSource>
    </appender>