In the continuing series on RSS files, DevShed has posted this new part with a focus on the "theoretical aspects" of developing an RSS file.
These aspects include things like examples of the elements it can contain, elements that are required for it to be a compliant RSS document, a look at the enhanced RSS functionality and structure (more information about the creator of the RSS embedded in the data), and even a look at what an aggregator is and what they would do with your RSS file.
Keep an eye out for the last installment in the series - a look at actually creating the RSS file from your data (probably from a database) and displaying it for the world to see.