This need not point to a location where the XML schema document is located.The target namespace of the XML schema is another URL, different from the XML schema location URL, which specifies an abstract namespace within which elements and types get declared.In the first part of this series we examined the default content type behavior, modeled after data-oriented documents, where complex type elements are element and attribute only, and simple type elements are character data without attributes.The W3C XML Schema Definition Language also supports the definition of empty content elements, and simple content elements (those that contain only character data) with attributes.
Because of confusion between XML Schema as a specific W3C specification, and the use of the same term to describe schema languages in general, some parts of the user community referred to this language as WXS, an initialism for W3C XML Schema, while others referred to it as XSD, an initialism for XML Schema Definition.
In Version 1.1 the W3C has chosen to adopt XSD as the preferred name, and that is the name used in this article.
In its appendix of references, the XSD specification acknowledges the influence of DTDs and other early XML schema efforts such as DDML, SOX, XML-Data, and XDR.
Empty content elements are defined using a regular Unlike DTDs, W3C XML Schema mixed content doesn't modify the constraints on the sub-elements, which can be expressed in the same way as simple content models.
While this is a significant improvement over XML 1.0 DTDs, note that the values of the character data, and its location relative to the child elements, cannot be constrained.