Schemas combine concepts from DTDs, relational databases, and object-oriented design. Schemas can describe the structure of XML documents, databases, directed-labeled-graphs, and other similar organizations of data. Schemas supply additional semantic information to documents, and contain new facilities such as as data types, inheritance, and extensibility that are not available in DTDs. Schemas use the same syntax as XML documents.
Schema components are reusable through the facility of XML namespaces.