A data source is simply a collection of key-value pairs. One specific datasource-entry is a set of two linked attributes: a key, which is a unique identifier for the item and the value.
Key-value pairs can be used for a single-choice, multiple-choice options and as well directly through our API to use them for multi-language labels, categories, or any use-case you might need key-value pairs.
You can load content entries from different spaces by using different access tokens for your requests. Your access tokens decide which space you want to access. Checkout Cache Invalidations if you want to know more about how you are able to invalidate the cache of your published content.