Fast and Slow Thinking: A Two-Step Schema-Aware Approach for Instance Completion in Knowledge Graphs

Modern Knowledge Graphs (KG) often suffer from an incompleteness issue (i.e., missing facts). By representing a fact as a triplet <inline-formula><tex-math notation="LaTeX">$(h,r,t)$</tex-math><alternatives><mml:math><mml:mrow><mml:mo>(</mml:mo><mml:mi>h</mml:mi><mml:mo>,</mml:mo><mml:mi>r</mml:mi><mml:mo>,</mml:mo><mml:mi>t</mml:mi><mml:mo>)</mml:mo></mml:mrow></mml:math><inline-graphic xlink:href="yang-ieq1-3304137.gif"/></alternatives></inline-formula> linking two entities <inline-formula><tex-math notation="LaTeX">$h$</tex-math><alternatives><mml:math><mml:mi>h</mml:mi></mml:math><inline-graphic xlink:href="yang-ieq2-3304137.gif"/></alternatives></inline-formula> and <inline-formula><tex-math notation="LaTeX">$t$</tex-math><alternatives><mml:math><mml:mi>t</mml:mi></mml:math><inline-graphic xlink:href="yang-ieq3-3304137.gif"/></alternatives></inline-formula> via a relation <inline-formula><tex-math notation="LaTeX">$r$</tex-math><alternatives><mml:math><mml:mi>r</mml:mi></mml:math><inline-graphic xlink:href="yang-ieq4-3304137.gif"/></alternatives></inline-formula>, existing KG completion approaches mostly consider a link prediction task to solve this problem, i.e., given two elements of a triplet predicting the missing one, such as <inline-formula><tex-math notation="LaTeX">$(h,r,? )$</tex-math><alternatives><mml:math><mml:mrow><mml:mo>(</mml:mo><mml:mi>h</mml:mi><mml:mo>,</mml:mo><mml:mi>r</mml:mi><mml:mo>,</mml:mo><mml:mo>? </mml:mo><mml:mo>)</mml:mo></mml:mrow></mml:math><inline-graphic xlink:href="yang-ieq5-3304137.gif"/></alternatives></inline-formula>. However, this task implicitly has a strong yet impractical assumption on the two given elements in a triplet, which have to be correlated, resulting otherwise in meaningless predictions, such as (<italic>Marie Curie</italic>, <italic>headquarters location</italic>, ? ). Against this background, this paper studies an instance completion task suggesting <inline-formula><tex-math notation="LaTeX">$r$</tex-math><alternatives><mml:math><mml:mi>r</mml:mi></mml:math><inline-graphic xlink:href="yang-ieq6-3304137.gif"/></alternatives></inline-formula>-<inline-formula><tex-math notation="LaTeX">$t$</tex-math><alternatives><mml:math><mml:mi>t</mml:mi></mml:math><inline-graphic xlink:href="yang-ieq7-3304137.gif"/></alternatives></inline-formula> pairs for a given <inline-formula><tex-math notation="LaTeX">$h$</tex-math><alternatives><mml:math><mml:mi>h</mml:mi></mml:math><inline-graphic xlink:href="yang-ieq8-3304137.gif"/></alternatives></inline-formula>, i.e., <inline-formula><tex-math notation="LaTeX">$(h,? ,? )$</tex-math><alternatives><mml:math><mml:mrow><mml:mo>(</mml:mo><mml:mi>h</mml:mi><mml:mo>,</mml:mo><mml:mo>? </mml:mo><mml:mo>,</mml:mo><mml:mo>? </mml:mo><mml:mo>)</mml:mo></mml:mrow></mml:math><inline-graphic xlink:href="yang-ieq9-3304137.gif"/></alternatives></inline-formula>. Inspired by the human psychological principle “fast-and-slow thinking”, we propose a two-step schema-aware approach RETA++ to efficiently solve our instance completion problem. It consists of two components: a <italic>fast</italic> RETA-Filter efficiently filtering candidate <inline-formula><tex-math notation="LaTeX">$r$</tex-math><alternatives><mml:math><mml:mi>r</mml:mi></mml:math><inline-graphic xlink:href="yang-ieq10-3304137.gif"/></alternatives></inline-formula>-<inline-formula><tex-math notation="LaTeX">$t$</tex-math><alternatives><mml:math><mml:mi>t</mml:mi></mml:math><inline-graphic xlink:href="yang-ieq11-3304137.gif"/></alternatives></inline-formula> pairs schematically matching the given <inline-formula><tex-math notation="LaTeX">$h$</tex-math><alternatives><mml:math><mml:mi>h</mml:mi></mml:math><inline-graphic xlink:href="yang-ieq12-3304137.gif"/></alternatives></inline-formula>, and a <italic>deliberate</italic> RETA-Grader leveraging a KG embedding model scoring each candidate <inline-formula><tex-math notation="LaTeX">$r$</tex-math><alternatives><mml:math><mml:mi>r</mml:mi></mml:math><inline-graphic xlink:href="yang-ieq13-3304137.gif"/></alternatives></inline-formula>-<inline-formula><tex-math notation="LaTeX">$t$</tex-math><alternatives><mml:math><mml:mi>t</mml:mi></mml:math><inline-graphic xlink:href="yang-ieq14-3304137.gif"/></alternatives></inline-formula> pair considering the plausibility of both the input triplet and its corresponding schema. RETA++ systematically integrates them by training RETA-Grader on the reduced solution space output by RETA-Filter via a customized negative sampling process, so as to fully benefit from the efficiency of RETA-Filter in solution space reduction and the deliberation of RETA-Grader in scoring candidate triplets. We evaluate our approach against a sizable collection of state-of-the-art techniques on three real-world KG datasets. Results show that RETA-Filter can efficiently reduce the solution space for the instance completion task, outperforming best baseline techniques by 10.61%–84.75% on the reduced solution space size, while also being 1.7×–29.6x faster than these techniques. Moreover, RETA-Grader trained on the reduced solution space also significantly outperforms the best state-of-the-art techniques on the instance completion task by 31.90%–105.02%.