How can I ensure the RSS data without repetition when fetch RSS data

Question

As we know, the RSS data will update if the website manager update it, or the third-part lib to update the RSS feed data.

Now if I am writing a RSS Reader, every time I fetch the data from the website's RSS source.

How can I ensure the data whether is fetched?

From the wikipedia RSS :

Only the title, link, description fields are required. the pubDate is not required. So, I can not insure the data whether is fetched by us via pubDate or other fields(like lastBuildDate field).

So, which friend can tell me how do you verify the feed data whether is fetched by us?

Answer 1

Finally I find the link can ensure a item whether is fetched.

I can save the fetched data in my database, every time the user fetch data, it can check the data whether is exists in the database by link property.