diff --git a/content/notes/13-databases-1.md b/content/notes/13-databases-1.md
index a69d871be..6c400f38a 100644
--- a/content/notes/13-databases-1.md
+++ b/content/notes/13-databases-1.md
@@ -66,7 +66,6 @@ three notations
 ![example data|400](https://i.imgur.com/t3fjN78.png)
 ![examle chen notation diagram|400](https://i.imgur.com/5a2TCXm.png)
 
-
 # how to model
 ## entities
 - a thing in the real world with independent existence
diff --git a/content/notes/ER-Diagram.md b/content/notes/ER-Diagram.md
index 8d19a2116..cb70d50dc 100644
--- a/content/notes/ER-Diagram.md
+++ b/content/notes/ER-Diagram.md
@@ -6,3 +6,18 @@ tags:
 ---
 
 
+Entity: a thing in the real world with *independent existence* (phsyical e.g., person or conceptual e.g., job)
+Entity type: A collection of entities 
+
+Attribute: properties of entity
+Attibute types:
+- simple/composite
+- single/multi valued
+- stored/derived
+- key (simple or composite)
+
+Relationship: when one entity refers to another
+Relationship type: a set of relationships with the same entity types
+- relationships can have attributes
+- relationships haveL
+
diff --git a/content/notes/databases.md b/content/notes/databases.md
index ea2d7c5b5..bc5a34cb9 100644
--- a/content/notes/databases.md
+++ b/content/notes/databases.md
@@ -5,11 +5,15 @@ tags:
 - cosc203
 ---
 
-# ER Diagram
+# Modelling
+Database: integrated collection of data
+- meaning
+- specific purpose
+
 [ER Diagram](notes/ER-Diagram)
+[Schemas](notes/Schemas)
+
 # Normal Forms
 [Normal Forms](notes/Normal-Forms)
-# Schemas
-[Schemas](notes/Schemas)
 # SQL
 [SQL](notes/SQL)
\ No newline at end of file