At the lowest level, each Yahoo! Maps API works the same way. Using REST, you can plot points on a map with features like custom descriptions, URLs, labels, groups, icons and more. Your data inputs need to be formatted in Web-standard RSS format with either longitude/latitude or address information, as you like. All Yahoo! Maps APIs can take actual address information and process the geocoding for you. No more messing with preprocessing to generate XML already encoded with latitude/longitude
Yahoo Maps API offers three ways to integrate maps into a website - a simple REST-based API for map images, an Ajax JavaScript API, and a Flash API. This summary refers to the AJAX API which is closest to Google and Microsoft models.
If you're looking to setup a Yahoo API for Wordpress XML sitemap, you might want to follow the easy directions @ this blog post: http://www.strictlyonlinebiz.com/blog/how-to-get-a-yahoo-application-id-for-xml-sitemap/1721/