A schema defines the structure of XML documents. It provides details about the content model: which elements it contains and in what order, what its content can be, and which content these attributes can contain.
A schema verifies that the incoming XML documents are in the expected format.
An XML schema can be used to:
Validate the content of an XML document.
Determine whether the XML document is a valid instance of the vocabulary (grammar or rules) expressed by the XML schema.
Describe the vocabulary for use by others creating XML documents.
Define the elements that can appear within an XML document and the attributes that can be associated with an element.
Define whether an element is empty or can include text.
Define a default value for an attribute.
Define elements that can contain child elements.
Define the sequence for child elements that appear in an element.
Define the number of child elements.