I agree we need a Series model and that it should not link to Book.

Whether it should be linked to a Work or an Edition however depends on what we mean by "series", and this needs to be made very clear in all documentation and user interfaces to avoid confusion. A couple of examples to illustrate what I mean:

Emma / Jane Austen

• Everyman's Library
• Penguin Classics
• Vintage Classics Austen Series
• etc

The Light Fantastic / Terry Pratchett

• Discworld (2)

Personally I would argue that in all the cases for Emma these are imprints rather than a "series", and therefore in our small example above only Discworld is a true series. But this is not necessarily obvious nor a universally held view (especially given that one of the imprints refers to itself as a "series"). The reason this matters is because imprints like "Penguin Classics" are only valid at an Edition level - the Everyman's Library edition is not part of the Penguin Classic "series". So how we define a series determines whether it links to Edition or Work, and vice-versa.