First ERB messaging

Documents/proto/messaging_extension/ERD.md

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+# Entity relational diagram
+
+## Messaging extension 
+
+```mermaid
+erDiagram
+
+%% General
+Users
+
+%% Messages
+Discussions{
+    Integer id PK
+    String name
+}
+
+Messages{
+    Integer id PK
+    Integer response FK "Messages"
+    String content
+}
+
+Discussions ||--o{ Messages: "" 
+Discussions ||--o{ Users: ""
+
+Messages o|--o{ Messages: "answers"
+
+%% Forums
+Forums{
+    Integer id PK
+    String name
+}
+
+Topics{
+    Integer id PK
+    String subject
+    String content
+    Boolean locked
+}
+Answers{
+    Integer id PK
+    String content
+    Boolean anonymous
+    TimeStamp creation_time 
+}
+
+Polls{
+    Integer id PK
+    enum PollType "ALLOW_NEW_OPTIONS ALLOW_MULTIPLE CHOICE"
+}
+Options{
+    Integer id PK
+    String name
+}
+
+Forums ||--o{ Users: "Registered"
+Forums ||--|| Teacher: "Owner"
+Forums ||--|| Course: ""
+Forums ||--o{ Topics: ""
+Forums ||--o{ Polls: ""
+
+Topics ||--|| Teacher: "Author"
+Topics ||--|| Users: "Author"
+Topics ||--o{ Answers: ""
+
+Polls ||--o{ Options: ""
+
+Options ||--o{ Votes : ""
+
+Votes }o--|| Users: "Voter"
+
+
+%% Appointments
+Teachers
+Appointments{
+    Integer id PK
+    TIME sent_time
+    enum Status
+}
+
+Appointments ||--|| Teachers: ""
+Appointments ||--|| Users: ""
+
+```
+
+Debucquoy Anthony