vault backup: 2022-10-24 22:45:59

content/notes/Normal-Forms.md

@@ -6,3 +6,14 @@ tags:
 ---
 
 
+# 1 NF
+- atomic attributes
+- no multivalue/composite/nested relations
+
+# 2 NF
+- no nonprime attributes that are partially functionally dependent on primary key
+
+# 3 NF
+- remove nonprime attributes that are transitively dependent on primary key
+
+# BCNF

content/notes/databases.md

@@ -28,9 +28,29 @@ Constraints
 - Ref Integrity: Foreign key 
 - Functional Dependencies
 	- fd: when one value determines another e.g., sid -> sname, {sid, cid}  -> grade
-	- armstrong axioms: 
+	- armstrong axioms: ![](https://i.imgur.com/3MAOrXD.png)
 
 # Normal Forms
+Help to prevent anomalies (update, delete, insert) by reducing redundancy
+
+e.g., 
+```
+bad:
+Student_Course(sid, sname, address, cid, cname, grade) 
+
+good:
+Student(sid,sname,address) 
+Course(cid,cname)
+nrolled(sid,cid,grade)
+```
+
+done through process of decomposition: breaking down schema into set of schemas while preserving:
+- attributes
+- dependencies
+- lossless joins
+
+Various degrees of normalisatin defined by normal forms: 
 [Normal Forms](notes/Normal-Forms)
+
 # SQL
 [SQL](notes/SQL)