OK, this isn't xsi format, it is SOAP format.
If you had to, you'd read it like any other XML Document.
However there is normally no need to do this. Normall there is a WSDL file associated with a web service, all you need to do is run WSDL.exe against the services WSDL file, and it generates proxy classes to talk to the service and Object model classes to deserialize the XML to objects. In this case AFACT, you'll get a BookReservation object (its been a long time since I used vanilla SOAP Services), with properties set to the values in the XML.
This will save you a lot of work hand-rolling your own proxies. See this for an article about using the WSDL:
http://my.execpc.com/~gopalan/dotnet/webservices/webservice_csharp_client.html[
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