Genres/ Subjects/ Categories in epub's metadata

Question

What is the proper way to define genre in epub's metadata? (in OEBPS/content.opf file.)

I can't google the definition, just some obviousness mentions like "It may also include many other things such as ... the genre" (link)

And, by the way, where can I find the current list of literary genres? (I found one in the wiki, but I'm not sure, is it applicable here or not.)

UPD 28.12.2019

I found in some downloaded epubs that genres are listed in several tags called subject from DDI-Codebook namespace, e.g.:

    <package xmlns:dc="http://purl.org/dc/elements/1.1/" ...>
    ...
    <dc:title>A Journey to the Centre of the Earth</dc:title>
    ...
    <dc:subject>Science fiction</dc:subject>
    <dc:subject>Adventure stories</dc:subject>
    <dc:subject>Earth (Planet) -- Core -- Fiction</dc:subject>
    <dc:subject>Voyages, Imaginary -- Fiction</dc:subject>

On the ddialliance.org I found a corresponding page with this obscure description:

Namespace: http://purl.org/dc/elements/1.1/

Type: SimpleLiteral, inherited from any

Content: mixed (allows character data), 1 attribute

Subst.Gr: may substitute for element any

Defined: globally in dc.xsd; see XML source

Used: never

Is it really correct to define genres in this tags? Or is it "de facto" standard without strict rule?

Answer 1

This field comes from the Dublin Core (DC) metadata standard, which is useful for interoperability between software and databases. I don't think there has emerged an accepted way to use DC metadata for ebook reading systems.

One idea might be to go with BISAC categories (as listed here). My memory could be mistaken, but I don't think the reading systems process these values in any meaningful way, (wouldn't that be nice if they did!) BTW, I seem to recall that Google Play required that you use BISAC codes when selling through them. For the DC metadata, don't use the alphanumeric value of the BISAC, just use a simple phrase based on BISAC values.

Here's a book marketing guy explaining BISAC vs. Amazon's categories. Here's more by this same book marketing guy.