Database ERD Diagrams and graph planarity -

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i wondering, erd diagram planar? have basic understand of database entity relationships, have been unable think of situation make erd diagram non-planar.

could please explain me whether or not erd diagram planar? if not, situation make non-planar? if yes, please provide small proof of why planar?

i have searched on internet , nobody seems have concrete answer this.

thank you.

could please explain me whether or not erd diagram planar?

i think it's matter of generating graph in manner displays graph in simple readable form. having algorithm strives achieve planar layout can organize complex erd diagram comes closer achieving goal. use visual paradigm generate erd diagrams; don't think it's case diagrams come out planar pretty close of time. exception occurs one-to-one, many-to-one, , one-to-many class relationships.

if yes, please provide small proof of why planar?

if graph not planar, want draw few crossings possible, because crossings decrease readability of drawing. since hard find drawing of non planar graph minimum number of crossings, use following approach compute drawing small number of crossings. first delete small number of edges given graph such resulting graph planar. compute drawing of planar subgraph without crossings. reinsert deleted edges drawing in such way number of edge crossings minimized. using approach, number of crossings of final drawing depends on planar subgraph , drawing of subgraph.

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

here exapmles:

http://www.codeproject.com/articles/14280/database-visualization http://www.ogdf.net/doku.php/tech:howto:plzl


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