Adds ERM

5-entity-relationship.md

@@ -0,0 +1,89 @@
+# Entity Relationship Diagrams
+
+## Example
+
+```mermaid
+erDiagram
+    User {
+        Int id PK
+        String username
+        Int serverId FK
+    }
+
+    Server {
+        Int id PK
+        String serverName
+    }
+
+    Server ||--o{ User : has
+```
+
+```
+erDiagram
+    User {
+        Int id PK
+        String username
+        Int serverId FK
+    }
+
+    Server {
+        Int id PK
+        String serverName
+    }
+
+    Server ||--o{ User : has
+```
+
+## Defining entities
+
+```mermaid
+erDiagram
+    User {
+        String Username PK "The user's name, a primary key"
+        Date dateCreated "When the user was created"
+        Int Server FK "The user's server, a foreign key"
+    }
+```
+
+```
+erDiagram
+    User {
+        String Username PK "The user's name, a primary key"
+        Date dateCreated "When the user was created"
+        Int Server FK "The user's server, a foreign key"
+    }
+```
+
+## Defining relationships
+
+### Numerical relationship
+
+```mermaid
+erDiagram
+    User1 |o--o| Item1 : "Zero or one - Zero or one"
+    User2 }o--o{ Item2 : "Zero or more - Zero or more"
+    User3 ||--|| Item3 : "Exactly one - Exactly one"
+    User4 }|--|{ Item4 : "One or more - One or more"
+```
+
+```
+erDiagram
+    User1 |o--o| Item1 : "Zero or one - Zero or one"
+    User2 }o--o{ Item2 : "Zero or more - Zero or more"
+    User3 ||--|| Item3 : "Exactly one - Exactly one"
+    User4 }|--|{ Item4 : "One or more - One or more"
+```
+
+### Identifying relationship
+
+```mermaid
+erDiagram
+    AppleTree ||..|| Apple : "Reliant entity"
+    Flower ||--|| Leaf : "Independent entities"
+```
+
+```
+erDiagram
+    AppleTree ||..|| Apple : "Reliant entity"
+    Flower ||--|| Leaf : "Independent entities"
+```

readme.md

@@ -85,10 +85,57 @@ classDiagram
 ```
 <a href="/3-class.md">3: Class diagram syntax</a></td></tr>
 <tr><td>
+
+```mermaid
+stateDiagram-v2
+    Stationary --> Moving : Begin moving
+    Moving --> Stationary : Stop moving
+```
+
 </td><td>
+
+```
+stateDiagram-v2
+    Stationary --> Moving : Begin moving
+    Moving --> Stationary : Stop moving
+```
+
 <a href="/4-state.md">4: State</a></td></tr>
 <tr><td>
+
+```mermaid
+erDiagram
+    User {
+        Int id PK
+        String username
+        Int serverId FK
+    }
+
+    Server {
+        Int id PK
+        String serverName
+    }
+
+    Server ||--o{ User : has
+```
+
 </td><td>
+
+```
+erDiagram
+    User {
+        Int id PK
+        String username
+        Int serverId FK
+    }
+
+    Server {
+        Int id PK
+        String serverName
+    }
+
+    Server ||--o{ User : has
+```
 <a href="/5-entity-relationship.md">5: Entity Relationship</a></td></tr>
 <tr><td>
 </td><td>