I'm trying to understand this paper and in Figure 1 page 389 there's a projection in the form of $\pi_{d.id : s.id}$. What does the colon mean? Because usually projections are simply $\pi_{name}(R)$
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$\begingroup$ What does the paper say it means? $\endgroup$– philipxyCommented Jan 1, 2022 at 18:30
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2$\begingroup$ Please put the paper identification details in your post, links die & posts should be self-contained. $\endgroup$– philipxyCommented Jan 1, 2022 at 19:46
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2$\begingroup$ We expect references to fulfill the minimal scholarly requirements and be as robust over time as possible. Please take some time to improve your post in this regard. We have collected some advice here. Thank you! $\endgroup$– D.W. ♦Commented Jan 1, 2022 at 22:54
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Colon in Π (project) seems to be attribute rename after projecting a la SQL SELECT AS, but in the order new attribute : old attribute. This is similar to its use in Γ (group by) for new attribute : value per pseudo aggregation function call.
Thus, the dependent join is executed on the projection of the students’ id only, i.e.:
. . . Π d.id:s.id ((students s ⋈ s.id=e.sid exams e) ⧑ (Γ ∅;m:min(e2.grade)(σ d.id=e2.sid exams e2)))
This interpretation seems to be needed to make sense of Figure 1 as we follow relation attribute sets from the root down or leaves up.
