Dear forum members,
let me prefix, I'm not a database developer but a user of a very large database and am using the SQL Developer to kind of reverse engineer the relations between the given tables.
I've been looking into the meaning of the arrow ends of the relational model for days and cannot find a conistent or complete answer anywhere. First of all, let me explain what I'm refering to, to prevent any confusion. If you have a look at any table there is the model tab, which shows a very helpful relational model of the selected table, e.g. ROOMS:
The relations between the individual tables are indicated by arrows with a variety of different tail ends. I know that in the default setting the arrow head points to the table with the primary key (which can be changed in the preferences). Here's a collection of some arrows I regulary come across:
However, there is no clear descripition of what the tail ends mean. I've read that it's supposed to be crow's foot notation, but it's not consistent with the description of crow's foot notation I've come across (https://vertabelo.com/blog/crow-s-foot-notation/). Crow's foot should have symbols on both side of the line and I've never seen an X as a part of crow's foot notation.
On another site I've read that the tail end indicates cardinality. Thereby, the larger symbol “>” is supposed to indicate the many side and the line “|” the 1 side. But I'm not sure about this, as in the actual crow's foot notation the “|” indicates mandatory and an “o” optional. So I'm under the impression that the SQL Developer uses a modification of the usual crow's foot notation.
I hope you can understand my confusion. Furthermore, I feel like this schema could be very helpful in understanding the relations between my given tables. But first I need to understand this arrow schema. I'd be very happy about an explanation of the arrow symbols or a hint where to find an exhausitve documentation of this topic - so far I couldn't find any documentation.
Thanks for reading and any help!