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I am trying to understand ERD diagrams. Searching for information, I came across the two following images on google. It is not clear to me which kind is actually the real ERD diagram:

Diagram 1:

enter image description here

Diagram 2: enter image description here

The second one is from a question on stackoverflow.com

Or can these diagrams be used interchangeably?

Christophe
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jarhead
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  • both are ER diagrams, they just use different *notations*, i.e. different symbols to represent the same concepts – Kurt Feb 24 '23 at 18:42
  • This site has white & black background modes, don't use images with transparency. – philipxy Feb 25 '23 at 02:08
  • The 1st is a Chen ERD, the other is not but claims to be & gets called that if you want to communicate with other people who call hem ERDs. Observe that in the latter you cannot tell the alleged Es from Rs since everything is either an E or an associative E although one might consider the Es to be the boxes that don't have any participations in (FKs referencing) other boxes. – philipxy Feb 25 '23 at 02:09
  • Does this answer your question? [What is the "Real" ER Diagram?](https://stackoverflow.com/questions/25720288/what-is-the-real-er-diagram) – philipxy Feb 25 '23 at 02:14
  • Please before considering posting: Pin down code issues via [mre]. Read manuals/references & google error messages & many clear, concise & precise phrasings of your question/problem/goal, with & without your particular names/strings/numbers, 'site:stackoverflow.com' & tags; read many answers. SO/SE search is poor & literal & unusual, read the help. Google re googling/searching, including Q&A at [meta] & [meta.se]. [How much research effort is expected of Stack Overflow users?](https://meta.stackoverflow.com/q/261592/3404097) [ask] [Help] Reflect research in posts. – philipxy Feb 25 '23 at 02:15

1 Answers1

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Both diagrams are ERD diagrams, but use two popular notation variants:

  • Diagram 1 uses Chen's notation: Chen was the inventor of the ERD concept and used this kind of diagram in his foundational paper, that paved the way to ERD modelling.

  • Diagram 2 uses Crow's foot notation: This notation was invented by Gordon Everest and was used before relational DBMS to show relationships between files. But its simplicity and intuitive reading quickly made it very popular for ERD.

The two notations can be used interchangeably in most of the cases. However, some advanced ER concepts exist natively in Chen's but cannot be mapped directly to Crow's foot notation (e.g. N-Ary relations, associative entities, weak entities and relations, ...) although some workarounds exist to deal with the limitations

Christophe
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