"Edition" is a really tricky concept.
FRBR doesn't specifically call out the concept, and there have been a lot of different interepretations, typically based on whatever's useful for a particular media being indexed and the organization doing the indexing. A change that one group might consider to be just a new Manifestation might be considered by someone else to be a new Expression, or even a new Work. (see the Library of Congress's What is FRBR? for a definition of Work, Expression and Manifestation).
The main example of problem 'editions' are text books -- most editions of the book are effectively teaching the same concepts, in the same order, but there may be enough changes to pagination, layout or example problems that make it impossible for a student to do the same homework based on page & question numbers. It's obviously a new Manifestation, but is it also a new Expression, or even a new Work?
For fiction, those problems don't tend to be as prevalent; there may be some content added (eg, a new foreward that puts the novel into a different context), but you don't tend to have as significant wholesale changes. You may have some differences in editions intended for different audiences, such as the additional footnotes and section in the American version of Good Omens
More typically, if there's something of this magnitude in a novel, it'd be in artwork, but this gets into other issues if the art was not part of the original book. (then you have a Manifestation with more than one Work: the original story plus the new artwork). I can think of at least one case where this was reversed, and the artwork removed in Stardust. In this case, we further complicate matters as the original publication was as a four part serial which was republished as a composite multiple times, then had the text portion stripped out which was also published in multiple forms. (and then made into a movie, but movie adapations are generally considered to be new Works in FRBR; I also won't get into if it was a 'Composite Work' vs. a 'Composite Manifestation' for the initial collected work, but that issue of how to model composites I don't believe has really been solved).
And then we get into issues of translations. Now, most people wouldn't consider the Spanish translation of a book originally in English to be a new 'edition' of a book, and many people model translations as a new Work ... but what do we do when there are multiple translations into the same language? Should they be considered editions of each other, or as seperate but related entities? For instance, we have classic poems such as Dante's Inferno, some translations that have attempted a more accurate translation while others attempt to maintain structure and rhyming. In a possibly more extreme case, we have the bible; there was a fair bit of disagreement over the 2011 NIV translation.
Where I've really seen the most problem isn't in books ... it's in movies. All of the 'Deluxe Edition', 'Special Edition', 'Director's Cut', widescreen vs. pan & scan, etc. And then you work in VHS vs. DVD vs. BluRay vs. HD-DVD vs. laserdisc, etc.
So ... with all of this said, I'd really suggest you follow Jakob's & wdenton's advice, and look into existing systems. It looks like oss4lib has handed off to foss4lib for their list of open source library software; if you have more specific requirements, you can try asking on the code4lib mailing list.