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We have not performed official tests with SQL 2014, that is why we cannot added as supported in the documentation. However, it should be ok, as long as OpenAccess supports it. Which is valid for the 2014 q1 SP1 release:http://www.telerik.com/support/whats-new/data-access/release-history/q1-2014-sp1. Sitefinity 7.0 uses this version, there should not be any issues.
I hope this helps.
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