For anyone interested in how the relational interpreter powering Barliman works, here is a short talk I gave at PolyConf last year:
https://www.youtube.com/watch?v=eQL48qYDwp4
And here is a much more in-depth two-part talk I gave at Lambda Lounge Utah:
https://www.youtube.com/watch?v=zHov3fKYqBA https://www.youtube.com/watch?v=nFE2E91VDAk