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A normal entity diagram usually use circles or a straight line to denote a zero or one to many relationship, respectively as in the following image:

enter image description here

However, recently I've seen something new, as in the following image, and was wondering what the cross means:

enter image description here

Dai
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moth
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  • I draw that myself, however I picked up from an ER established database at work. – moth Oct 15 '22 at 03:43
  • Are you able to inspect the database that _that_ ER diagram referred to? If so, just dump the foreign-key definitions and see if there's anything unusual about it. – Dai Oct 15 '22 at 03:45
  • hum I'm new to database logic, how would I do that ? – moth Oct 15 '22 at 03:47
  • What DBMS is the database running in? – Dai Oct 15 '22 at 03:48
  • oracle db...... – moth Oct 15 '22 at 03:48
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    Use the `desc` command in Oracle to get object definitions: https://stackoverflow.com/questions/18264584/show-create-table-equivalent-in-oracle-sql – Dai Oct 15 '22 at 03:49
  • I've done the following: `select * from all_cons_columns where table_name = ` and I got that the foreign key has a `SYS_*` constraint name and `TABLE_UK` and `TABLE_FK` i.e. unique and foreign (UF) key constraint. `desc` command just tells me `not null number(8)` – moth Oct 15 '22 at 04:30
  • Sounds like the X refers to the `UNIQUE` constraint then. – Dai Oct 15 '22 at 04:32

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