If you specify the length, you cannot specify the maximum or minimum (or vice versa).
The values for xsd:length, xsd:minLength, and xsd:maxLength must all be non-negative integers.
If the element is based on a binary type, the length limits the number of octets of binary data.
If the element is derived by list, the length determines the number of list items.
File: Schema.xsd
<?xml version="1.0"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://www.java2s.com" xmlns="http://www.java2s.com"
elementFormDefault="qualified">
<xsd:element name="animal_code">
<xsd:simpleType>
<xsd:restriction base="xsd:string">
<xsd:length value="4" />
</xsd:restriction>
</xsd:simpleType>
</xsd:element>
</xsd:schema>
File: Data.xml
<?xml version="1.0"?>
<animal_code xmlns="http://www.java2s.com">TIGR</animal_code>