vault backup: 2022-10-24 22:30:59

content/notes/ER-Diagram.md

@@ -19,5 +19,12 @@ Attibute types:
 Relationship: when one entity refers to another
 Relationship type: a set of relationships with the same entity types
 - relationships can have attributes
-- relationships haveL
+- relationships have:
+	- degree (bi/n-ary)
+	- cardinality (1:1, 1:N N:M)
+	- participation constraints (total (marked by double line) or partial)
 
+Weak entities
+- no key attributes
+- requires total participation constraint on identifying relationship to its identifying entity type
+- partial key used in combination with identifying entity

content/notes/databases.md

@@ -13,6 +13,23 @@ Database: integrated collection of data
 [ER Diagram](notes/ER-Diagram)
 [Schemas](notes/Schemas)
 
+# Relational Model
+Two parts
+- Relation Schema
+- Domain
+
+Constraints
+- Domain: each value must an atomic value in the domain e.g., integer, string, date, etc
+- Key and NULL: 
+	- Superkey: uniquely ids a tuple e.g., set of all attrs
+	- Key: minimal superkey
+	- Candidate key: a possible key
+	- Primary key: the chosen candidate key: cannot have NULL values
+- Ref Integrity: Foreign key 
+- Functional Dependencies
+	- fd: when one value determines another e.g., sid -> sname, {sid, cid}  -> grade
+	- armstrong axioms: 
+
 # Normal Forms
 [Normal Forms](notes/Normal-Forms)
 # SQL