Create Cal360

As requested at the last SDW-IG plenary telco.

proposals/Cal360

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+The W3C SDW WG deliverable and W3C Recommendation Time Ontology in OWL [1], since its publication in October 2017, has some evidence of usage, both novel and to replace the previous 2006 version. One (or more?) minor correction is also being discussed and resolved.
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+This proposal is to construct a simple ontology and notation to use in conjunction with the Time Ontology in OWL to allow climate and earth system scientists to annotate climatological datasets that have used a 360 day approximation to the internationally established Gregorian calendar. The 360 day calendar allows easy calculations of monthly and quarterly statistics, as all 'months' have 30 days. Comparison of simulated monthly statistics is not good practice as the errors in the number of days is of the order of 10%, whereas errors of comparing quarters is of the order of 1 or 2%.
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+How to map individual days or weeks, or even 'month's, to the real-world Gregorian months will not be specified, as this depends on the science and assumptions of the scientific experiments being undertaken.
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+It is envisaged that some terminology will be needed to distinguish the 'calendar' from others, and the names of the 'month's. 
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+It is also envisaged that the experience of this work will contribute to developing other 'real-world' calendar onotologies used by different communities, again building on the underpinning Time Ontology in OWL.
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+[1} https://w3c.github.io/sdw/time/