From 3f993adc01749b56b37899043936b0b18869bccf Mon Sep 17 00:00:00 2001
From: Ryan <ryan@alien.gov>
Date: Wed, 14 Jun 2023 15:11:30 +0800
Subject: [PATCH] Auto saved by Logseq

---
 pages/总复习2023t1.md | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/pages/总复习2023t1.md b/pages/总复习2023t1.md
index 96439cc..289cf16 100644
--- a/pages/总复习2023t1.md
+++ b/pages/总复习2023t1.md
@@ -1002,6 +1002,12 @@
 						- Subclass :-> A distinct subgrouping of occurrences of an entity
 						  id:: 64895f39-d886-436b-9afe-ba75d37c8b45
 						  type.
+						- When to use them? eith
+						  1. There are attributes that apply to some (but
+						  not all) instances of an entity.
+						  2. The instances of a potential subclass
+						  participate in a relationship unique to that
+						  subclass.
 				- LATER designing ER diagram
 			- DONE Block 3
 			  collapsed:: true