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A comment on How category theory is applied. Parent comment

Re:How category theory is applied by wisnesky on Tuesday April 30, 2019 @05:52AM (#19786480)
Yes, for example the dual of join (called 'sigma'), which only exists for databases in categorical normal form. There are many academic papers and an open-source project ('categorical query language') here: http://www.categoricaldata.net.
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Re:How category theory is applied by twic on Tuesday April 30, 2019 @08:12AM (#19787188)
Sounds interesting! I had a look, but couldn't find out what sigma does. This is not quite the same level as, say, the PostgreSQL documentation:

http://www.categoricaldata.net/help/instancesigma.html

Is there somewhere i can go for a worked example of using sigma?

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Re:How category theory is applied by wisnesky on Tuesday April 30, 2019 @02:19PM (#19790516)
Sure, here is an example that uses sigma to compute an equivalence relation:

http://cql.conexus.ai/quotient.php

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