XML in a Nutshell, 3rd Edition

Document Organization

Now that there is a basic schema and a valid document from which to work, it is time to examine the structure of a schema document and its contents. Every schema document consists of a single root xs:schema element. This element contains declarations for all elements and attributes that may appear in a valid instance document.

Tip

The XML elements that make up an XML Schema must belong to the XML Schema namespace (http://www.w3.org/2001/XMLSchema), which is frequently associated with the xs: prefix. For the remainder of this chapter, all schema elements will be written using the xs: prefix to indicate that they belong to the Schema namespace.

Instance elements declared using top-level xs:element elements in the schema (immediate child elements of the xs:schema element) are considered global elements. For example, the simple schema in Example 17-2 globally declares one element: fullName. According to the rules of schema construction, any element that is declared globally may appear as the root element of an instance document.

In this case, since only one element has been declared, that shouldn’t be a problem. But when building more complex schemas, this side effect must be taken into consideration. If more than one element is declared globally, a schema-valid document may not contain the root element you expect.

Naming conflicts are another potential problem with multiple global declarations. When writing schema declarations, it is an error to declare two things ...