“…Due to time constraints, we will only provide pointers to other exciting extensions, including those to machine learning [3,57,62,79,85,86], degree information [6,53], inequalities [2], negation [58], result compression [20], dynamic settings [46,47,56], and approaches aiming for stronger notions of optimality [59,75]. It is also worth noting that some of these novel join algorithms have been implemented in prototype systems for graph processing [1,45,55]. A historical perspective on WCO join algorithms together with open problems in the area have recently been summarized by Ngo [74].…”