add documentation

docs/entity_relationship_diagram.md

@@ -2,17 +2,21 @@
 
 The Publication Email Request Service (PERS) relies on a database to keep track of the email requests that have been sent by stakeholders. Monitoring the email requests via database prevents duplication of email requests. The diagram describes the relationships between entities, or tables, in the database.
 
-The relationships depicted in the diagram can be summarized as follows:
-* A `Liaison` belongs to **one** `DLC`.
-* A `DLC` is assigned to **one or more** authors.
-* A `Publication (needing request)` can be associated with **one or more** `Author(s)`.
-* A `Publication (needing request)` can only be included in **one** `Email`; an `Email` can include **one or more** `Publication(s)`.
-* When an `Email` is created, it is assigned to **one** `Author` and **one** `Liaison`.
+The entities involved in PERS are as follows:
+
+* `DLC`: Represents a department, lab, or center at MIT and is managed by a single **liaison**. A **DLC** can comprise of many **authors**, but an author is assigned to a single **DLC**.
+* `Liaison`: Represents a DLS staff member on MIT's Scholarly Communications team. **Liaisons** are assigned to one or more **DLCs**. **Liaisons** receive the email requests generated by PERS, who then send the email to authors in their assigned DLCs.
+* `Author`: Represents MIT student and faculty who are registered on Symplectic Elements. An **author** is assigned to a single **DLC**. When citations are imported for an author, zero or more **Publications** may be found that require submission.
+* `Publications`: Represents a publication written by one or more **Authors**.
+* `Email`: Represents an email request for a publication. Many **publications** may be associated with a single **email**. The email generated by PERS will contain a list of citations for publications that need submission. 
+
+   **Note:** According to Solenoid documentation, authors on a single publication will receive **at most one (1)** email for a publication. However, (TO BE CONFIRMED) this is only if, when they're data is imported, the publication appears as not having been requested yet (via a second author that was previously imported through PERS).
 
 ```mermaid
 erDiagram
     publication["Publication (needing request)"]{
-        string id PK 
+        string publication_id PK 
+        string author_id PK
         string title
         string citation
         string email_id FK
@@ -41,8 +45,8 @@ erDiagram
         richtext latest_text
         date date_sent
     }
-    liaison }o--o| dlc: "belongs to"
-    dlc ||--|{ author: has
+    liaison |o--o{ dlc: "belongs to"
+    dlc ||--o{ author: has
     author }|--o{ publication: has
     publication }o--|| email: "included in"
     author ||--o{ email: receives