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docs/entityRelationshipDiagram.md

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 # Entity Relationship Diagrams
 
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 > An entity–relationship model (or ER model) describes interrelated things of interest in a specific domain of knowledge. A basic ER model is composed of entity types (which classify the things of interest) and specifies relationships that can exist between entities (instances of those entity types). Wikipedia.
 
 Note that practitioners of ER modelling almost always refer to _entity types_ simply as _entities_. For example the `CUSTOMER` entity _type_ would be referred to simply as the `CUSTOMER` entity. This is so common it would be inadvisable to do anything else, but technically an entity is an abstract _instance_ of an entity type, and this is what an ER diagram shows - abstract instances, and the relationships between them. This is why entities are always named using singular nouns.
@@ -50,6 +48,26 @@ erDiagram
     }
 ```
 
+```mermaid
+erDiagram
+    CUSTOMER ||--o{ ORDER : places
+    CUSTOMER {
+        string name
+        string custNumber
+        string sector
+    }
+    ORDER ||--|{ LINE-ITEM : contains
+    ORDER {
+        int orderNumber
+        string deliveryAddress
+    }
+    LINE-ITEM {
+        string productCode
+        int quantity
+        float pricePerUnit
+    }
+```
+
 When including attributes on ER diagrams, you must decide whether to include foreign keys as attributes. This probably depends on how closely you are trying to represent relational table structures. If your diagram is a _logical_ model which is not meant to imply a relational implementation, then it is better to leave these out because the associative relationships already convey the way that entities are associated. For example, a JSON data structure can implement a one-to-many relationship without the need for foreign key properties, using arrays. Similarly an object-oriented programming language may use pointers or references to collections. Even for models that are intended for relational implementation, you might decide that inclusion of foreign key attributes duplicates information already portrayed by the relationships, and does not add meaning to entities. Ultimately, it's your choice.
 
 ## Syntax
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     }
 ```
 
+```mermaid
+erDiagram
+    CAR ||--o{ NAMED-DRIVER : allows
+    CAR {
+        string registrationNumber
+        string make
+        string model
+    }
+    PERSON ||--o{ NAMED-DRIVER : is
+    PERSON {
+        string firstName
+        string lastName
+        int age
+    }
+```
+
 The attributes are rendered inside the entity boxes:
 
 ```mermaid-example
@@ -140,6 +174,22 @@ erDiagram
     }
 ```
 
+```mermaid
+erDiagram
+    CAR ||--o{ NAMED-DRIVER : allows
+    CAR {
+        string registrationNumber
+        string make
+        string model
+    }
+    PERSON ||--o{ NAMED-DRIVER : is
+    PERSON {
+        string firstName
+        string lastName
+        int age
+    }
+```
+
 The `type` and `name` values must begin with an alphabetic character and may contain digits, hyphens or underscores. Other than that, there are no restrictions, and there is no implicit set of valid data types.
 
 #### Attribute Keys and Comments