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Merge pull request #1346 from spopida/develop
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Fix docs for ER diagrams
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GDFaber committed Apr 10, 2020
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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.
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.

Mermaid can render ER diagrams
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## Status

ER diagrams are a new feature in Mermaid and are **experimental**. There are likely to be a few bugs and constraints, and enhancements will be made in due course.
ER diagrams are a new feature in Mermaid and are **experimental**. There are likely to be a few bugs and constraints, and enhancements will be made in due course. Currently you can only define entities and relationships, but not attributes.

## Syntax

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| Value (left) | Value (right) | Meaning |
|:------------:|:-------------:|--------------------------------------------------------|
| `|o` | `o|` | Zero or one |
| `||` | `||` | Exactly one |
| `\|o` | `o\|` | Zero or one |
| `\|\|` | `\|\|` | Exactly one |
| `}o` | `o{` | Zero or more (no upper limit) |
| `}|` | `|{` | One or more (no upper limit) |
| `}\|` | `\|{` | One or more (no upper limit) |

### Identification

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