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Asked: 2026-05-31T01:33:30+00:00

I am wondering, will an ERD diagram always be planar? I have a basic

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I am wondering, will an ERD diagram always be planar? I have a basic understand of database entity relationships, so currently I have been unable to think of a situation that would make an ERD Diagram non-planar.

Could someone please explain to me whether or not an ERD diagram would always be planar? If not, what situation would make it non-planar? If yes, could someone please provide a small proof of why it would always be planar?

I have searched on the internet and nobody seems to have a concrete answer for this.

Thank you.

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  1. Editorial Team

    Could someone please explain to me whether or not an ERD diagram would always be planar?

    I think it’s just a matter of generating the graph in a manner which displays the graph in its most simple readable form. Having an algorithm which strives to achieve this planar layout can help organize a complex ERD diagram so it comes closer to achieving this goal. I use Visual Paradigm to generate most my ERD diagrams; I don’t think it’s always the case the diagrams come out planar but they are pretty close most of the time. The exception usually occurs with one-to-one, many-to-one, and one-to-many class relationships.

    If yes, could someone please provide a small proof of why it would always be planar?

    If a graph is not planar, we want to draw it with as few crossings as possible, because crossings significantly decrease the readability of a drawing. Since it is very hard to find a drawing of a non planar graph with the minimum number of crossings, we use the following approach to compute a drawing with a small number of crossings. We first delete a small number of edges from the given graph such that the resulting graph is planar. Then we compute a drawing of this planar subgraph without crossings. Finally we reinsert the deleted edges into this drawing in such a way that the number of edge crossings is minimized. Using this approach, the number of crossings of the final drawing depends on the planar subgraph and the drawing of this subgraph.

    https://www.ads.tuwien.ac.at/research/graphDrawing.html

    Here are some exapmles:

    http://www.codeproject.com/Articles/14280/Database-Visualization
    http://www.ogdf.net/doku.php/tech:howto:plzl

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