problem with xsd file creation

Hi every one,
I am new to xml data files,I have two xml files with same data but only small difference as shown below

<List>
    <number>1101</number>
  <Area>inner walls in a room.</Area>
  <Detection>less pressure.</Detection>
  <reason>
    <normal>
      <Component Num="15" Type="electric">
        <Beha Num="97" working="yes" acceptrate="100"/>
      </Component>
    </normal>
  </reason>
  <reaction>
    <Informal/>
  </reaction>
  <action>
    <Informal>some data here.
</Informal>
  </action>
</list>

second xml file

<List>
    <number>1102</number>
  <Area>outside  of  room.</Area>
  <Detection>more pressure.</Detection>
  <reason/>
  <reaction>
    <Informal/>
  </reaction>
  <action/>
</list>

In the above two xml files the difference is in second xml file i Have two empty tag elements One is action and another is reason tags. I created one xsd file file using xmlpad for frist xml file and validated using that xsd , Its giving no errors, but when I tried same xsd for second xml file it giving error like.

element action{}has invalid structure for schema definition:(informal)

used xsd is like this

  <xs:element name="Action">
    <xs:complexType>
      <xs:sequence>
        <xs:element ref="Informal" minOccures="0"/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>
<xs:element name="Informal" type="xs:string"/>

same error for reason tags also, I tried in different ways but problem not solved can any one suggest me how to solve this problem.
Thanks in advance.

Why not have no action tag, instead of an empty one?