XSD stands for XML Schema Definition.It define the structure of the XML file and the elements and attributes it contains.The datatype of the elements.So that when u populate XML data into dataset, the dataset can treat elements differently based on their type.If XSD is not present dataset treats all elements as string type. XSLT stands for XML style sheet lang tranformation.It is lang used for transforming XML data in one format to another format.Example XML data into HTML format. XSLT uses XPath to identify the elements in XML doc and transform those to desired format