.XSD File Extension
What is an XSD file?
An XSD file is a file used to define what elements and attributes may appear in an XML document. It also defines the relationship of the elements and what data may be stored in them. XSD files are written in the W3C XML Schema language.
An XSD file stores its contents as plain text in XML format, which means the files can be opened and viewed by any text editor and numerous other programs. However, if you want to edit an XSD file, you should use an XML editor, such as Microsoft XML Notepad, Bare Bones BBEdit, or SyncRO Soft oXygen XML Editor.
NOTE: XSD files may be used as an alternative to Document Type Definition (.DTD) files for defining XML schemas.