An XML schema is a description of a type of XML document, typically expressed in terms of constraints on the structure and content of documents of that type, above and beyond the basic syntactical constraints imposed by XML itself.
These constraints are generally expressed using some combination of grammatical rules governing the order of elements, Boolean predicates that the content must satisfy, data types governing the content of elements and attributes, and more specialized rules such as uniqueness and referential integrity constraints.
However, when the user selects the XML document catalog1.xml, validation fails for the book element in the lines containing more than one title element.
See also: Robin Cover's index of XML Schema materials.All XML documents must be well-formed, but it is not required that a document be valid unless the XML parser is "validating", in which case the document is also checked for conformance with its associated schema.DTD-validating parsers are most common, but some support XML Schema or RELAX NG as well.XML Schema 1.1 Part 2: Datatypes and XML Schema 1.1 Part 1: Structures are available. Open Visual Studio and create a XML file as in the following:2.XML (1.0 and 2.0), XSV, the Saxonica XSD Validator and all other validating XSD parsers (or DTD parsers).