Fetching the data

To fetch your posts, you’d utilize the HTTP_API, fetch_feed() or SimplePie. This completely depends on how and from where you’re going to get the XML.

Here’s one answer about the HTTP API](https://wordpress.stackexchange.com/a/73659/385) and another one.

Storing & maintaining the data

The main problem will be that you need a storage location. Therefore you’d go and set up a Custom Post Type and maybe some Custom Taxonomies as well. Just make sure that they’re properly registered to each other. The tough part will be inserting, updating and deleting the post data, meta data, authors and taxonomies terms.

Retrieving the data on interval

Normally you’d utilize the Transient API and/or the Schedule/Cron API.