XSD Restriction on Attribute - attributes

Question

I think I have searched a lot about this but still no go.
Will appreciate any help.
I am trying to restrict an attribute for an element with empty content. "color" should have a restriction to only hold 3 digit or minLength=3 and maxLength=3. It should not have any content.
<?xml version="1.0" encoding="utf-8"?>
<items xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="">
<product id="" name="">
<article id="1001">
<umbrella color="100"/>
<umbrella color="101"/>
</article>
<article id="1002">
<umbrella color="110"/>
</article>
</product>
</items>
EDIT: I know how to do a XSD Restriction on a simpleType. But I don't how to combine it to one entity with a ComplexType.
If you could provide a more detailed (or full) solution I would be happy.
Btw, "color" is not limited to xs:integer. It is actually a xs:string.

Answer 1

You can define your attribute similar to the following. This example uses a pattern to restrict the value, but you could also use min and max if that's more appropriate.
<xs:attribute name="color">
<xs:simpleType>
<xs:restriction base="xs:integer">
<xs:pattern value="[0-9][0-9][0-9]"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
Then in your element definition, you just use a ref to reference the defined attribute:
<xs:attribute ref="color"/>
UPDATE (in response to comment from OP):
Here's what the entire schema might look like:
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:attribute name="color">
<xs:simpleType>
<xs:restriction base="xs:integer">
<xs:pattern value="[0-9][0-9][0-9]"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="id">
<xs:simpleType>
<xs:restriction base="xs:integer">
<xs:pattern value="[0-9][0-9][0-9][0-9]"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="name" type="xs:string"/>
<xs:complexType name="article_type">
<xs:attribute ref="color" use="required"/>
</xs:complexType>
<xs:element name="article">
<xs:complexType>
<xs:choice maxOccurs="unbounded" minOccurs="0">
<xs:element name="umbrella" type="article_type"/>
</xs:choice>
<xs:attribute ref="id" use="required"/>
</xs:complexType>
</xs:element>
<xs:element name="product">
<xs:complexType>
<xs:choice maxOccurs="unbounded" minOccurs="0">
<xs:element ref="article"/>
</xs:choice>
<xs:attribute ref="id" use="required"/>
<xs:attribute ref="name"/>
</xs:complexType>
</xs:element>
<xs:element name="items">
<xs:complexType>
<xs:choice maxOccurs="unbounded" minOccurs="0">
<xs:element ref="product"/>
</xs:choice>
</xs:complexType>
</xs:element>
</xs:schema>

Answer 2

The following should work
<element name="umbrella" nillable="true" type="umbrellaType">
<complexType name="umbrellaType">
<attribute name="color">
<simpleType>
<restriction base="int">
<minExclusive value="99"></minExclusive>
<maxInclusive value="999"></maxInclusive>
</restriction>
</simpleType>
</attribute>
</complexType>