<configSections>
<section name="dbFactory" type="DbFactory.Configuration.DbFactorySection,DbFactory.Configuration"/>
</configSections>

  <configSections>
        <section name="dbFactory" type="DbFactory.Configuration.DbFactorySection,DbFactory.Configuration"</configSections>

    <dbFactory>
        <default factory="sql"></default>
        <factorys>
            <add name="sql"  assembly="Hello.Data"  class="SqlDbFactory" />
            <add name="oracle" assembly="Hello.Data" class="OracleDbFactory" />            　
        </factorys>
    </dbFactory>

 public class DefaultElement : ConfigurationElement
    {
        [ConfigurationProperty("factory")]
        public string Factory
        {
            get
            {
                return this["factory"] as string;
            }
            set
            {
                this["factory"] = value;
            }
        }
    }

public class FactoryElement : ConfigurationElement
    {
        [ConfigurationProperty("name")]
        public string Name
        {
            get
            {
                return this["name"] as string;
            }
            set
            {
                this["name"] = value;
            }
        }

        [ConfigurationProperty("assembly")]
        public string Assembly
        {
            get
            {
                return this["assembly"] as string;
            }
            set
            {
                this["assembly"] = value;
            }
        }

        [ConfigurationProperty("class")]
        public string Class
        {
            get
            {
                return this["class"] as string;
            }
            set
            {
                this["class"] = value;
            }
        }
    }
public class FactoryElements : ConfigurationElementCollection
    {
        protected override ConfigurationElement CreateNewElement()
        {
            return new FactoryElement();
        }

        protected override object GetElementKey(ConfigurationElement element)
        {
            return ((FactoryElement)element).Name;
        }

        public FactoryElement this[string name]
        {
            get
            {
                return BaseGet(name) as FactoryElement;
            }
        }
    }

public class DbFactorySection : ConfigurationSection
    {
        [ConfigurationProperty("default")]
        public DefaultElement DefaultFactory
        {
            get
            {
                return this["default"] as DefaultElement;
            }
            set
            {
                this["default"] = value;
            }
        }

        [ConfigurationProperty("factorys")]
        public FactoryElements Factorys
        {
            get
            {
                return this["factorys"] as FactoryElements;
            }

            set
            {
                this["factorys"] = value;
            }
        }
    }