XML Schema Diagrams
Altova website: 
XML Schemas in UML
UModel supports the import and generation of W3C XML schemas as well as their forward and reverse engineering. In case of XML Schemas, "forward and reverse engineering" means that you can import a schema (or multiple schemas from a directory) into UModel, view or modify the model, and write the changes back to the schema file. When you synchronize data from the model to a schema file, the schema file is always overwritten by the model.
| Note: | The XML Schema must be valid before it can be imported into UModel. XML Schemas are not validated when you create or import them in UModel, or when you run a project syntax check. Nevertheless, UModel checks whether the XML schema is well-formed when importing it. |
XML Schema diagrams display schema components in UML notation. For example, simple types are shown in UModel as data types with the «simpleType» stereotype. Complex types are shown as classes with the «complexType» stereotype. Various schema details are represented as Tagged Values, while schema annotations are represented as comments. For a mapping table that illustrates how all the XML schema components map to UModel elements, see XML Schema Mappings.
Example XML Schema diagram