What is an XML namespace?
An XML namespace is a collection of element type and attribute names. The collection itself is unimportant; what is important is its name — a URI. This allows XML namespaces to provide a two-part naming system for element types and attributes. The first part of the name is the URI of the XML namespace — the namespace URI. The second part is the element type or attribute name itself — the local part, also known as the local name. Together, they form the universal name. This two-part naming system is the only function of XML namespaces. By using multiple XML namespaces, multiple element types with the same local name can inhabit the same XML document. For example, the following document uses XML namespaces to distinguish between two different element types named Address.
An XML namespace is a collection of element type and attribute names. The collection itself is unimportant — in fact, a reasonable argument can be made that XML namespaces don’t actually exist as physical or conceptual entities (see Namespace Myth #1). What is important is the name of the XML namespace, which is a URI reference. This allows XML namespaces to provide a two-part naming system for element types and attributes. The first part of the name is the URI reference used to identify the XML namespace — the namespace name. The second part is the element type or attribute name itself — the local part, also known as the local name. Together, they form the expanded name. This two-part naming system is the only thing defined by the XML namespaces recommendation.
