How to write condition in XML Schema?

[zedstar]

Is it possible to write condition in XML schema? I need to write restriction for start and end time. So that difference between start and end time must be greater than 1:00 hour. I am not sure how to do that? Sorry for my english i am not native speaker and thanks for help in advance.\[code\] <?xml version='1.0' ?> <course xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="schema.xsd"> <footnote></footnote> <sln>10637</sln> <prefix>ACCTG</prefix> <crs>230</crs> <lab></lab> <sect>01</sect> <title>INT FIN ACCT</title> <credit>1.0</credit> <days>TU,TH</days> <times> <start>7:45</start> <end>9:00</end> </times> <place> <bldg>TODD</bldg> <room>230</room> </place> <instructor>B. MCELDOWNEY</instructor> <limit>0112</limit> <enrolled>0108</enrolled></course>\[/code\]