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(Note that the SimplyE mobile app doesn't actually support navigation feeds yet. Grouped feeds offer a nicer version of the same functionality, but it's more work on your end.)
If your OPDS feed is intended for distributing books through other institutions, rather than for direct consumption by the SimplyE App, you should probably just create a simple paginated list of books with the newest books at the top.
Static generation
In most cases, it's preferable to generate your OPDS feeds statically ahead of time. As your collection becomes more complicated, it may be more practical to generate OPDS feeds as needed and cache them.
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