On 21 Aug 01, at 18:28, alan.gauld@freenet.co.uk wrote: > approach would be to model it ina layered fashion. Has anyone > else done this? OIf so where can I get a reerence? 3 typos in two lines - Doh! My new mail client has a spell checker, I really must get used to using it before I send. Sorry for that. Alan G