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# XSD Attributes * * * All attributes are declared as simple types. * * * ## What Is an Attribute? Simple elements cannot have attributes. If an element has attributes, it is considered a complex type. However, attributes themselves are always declared as simple types. * * * ## How to Declare an Attribute? The syntax for defining an attribute is: Here, xxx is the attribute name, and yyy specifies the data type of the attribute. XML Schema provides many built-in data types. ### The most commonly used types are: * xs:string * xs:decimal * xs:integer * xs:boolean * xs:date * xs:time ### Example This is an XML element with an attribute: Smith This is the corresponding attribute definition: * * * ## Default and Fixed Values for Attributes Attributes may have specified default or fixed values. A default value is automatically assigned to the element when no other value is specified. In the following example, the default value is "EN": A fixed value is also automatically assigned to the element, and you cannot specify another value. In the following example, the fixed value is "EN": * * * ## Optional and Required Attributes By default, attributes are optional. To specify that an attribute is required, use the "use" attribute: * * * ## Restrictions on Content When an XML element or attribute has a defined data type, restrictions are applied to its content. If an XML element's type is "xs:date", and its content is a string like "Hello World", the element will fail validation. With XML Schema, you can also add your own restrictions to XML elements and attributes. These restrictions are called facets.