XML Schema

XML Schema, often referred to as XML Schema Definition (XSD), is a language used to define the structure, content, and semantics of [[Extensible Markup Language|XML]] documents. XML Schema provides a more powerful and rigorous alternative to [[DTD (Document Type Definition)]], the original XML document validation schema language.

XML Schema is used to define the structure and data types of elements and attributes in an XML document. It specifies what elements are present, their order, and their data types. Unlike DTDs, XML Schema supports a wide range of data types, including string, integer, decimal, date, time, and more. It also allows for the creation of custom data types.

Schemas are used to validate XML documents, ensuring they conform to a predefined structure and set of rules. This is crucial for data integrity and reliability in XML data interchange. XML Schema supports XML namespaces, allowing for the creation of fully-qualified names to avoid naming conflicts across XML documents.

XML Schema can describe complex data structures, including nested and repeated elements, which is a limitation in DTDs. Elements defined in one XML Schema can be reused in other schemas, promoting modularity and reducing redundancy.

When validating XML documents against an XML Schema, specific and detailed error messages can be generated, helping in troubleshooting and correcting structure or data issues. XML Schema is widely adopted in various industries for defining XML document structures, and there are many tools available for creating, editing, and validating XSDs.

In the context of web services, especially [[SOAP|SOAP]]-based services, XML Schema plays a crucial role in defining the structure of request and response messages.

XML Schema is often used in conjunction with other XML-based technologies, like [[XSLT (Extensible Stylesheet Language Transformations)|XSLT]] and [[XPath]], for comprehensive XML document processing.