Originally Posted by travelingman
One document that has been leaked states that XKeyscore has the capabilities to read the content of emails. The only requirements that an NSA employee needs to read the content of the emails of the person under scrutiny after providing a selector is to meet the requirements of the 51% standard. Also, Snowden has stated that NSA employees are hardly brought to accountability for their search entries, and even when they are, it's unlikely the employee faces any drawback.
The Guardian published a marketing/training document where every example was about metadata and about foreign targets. Also it was from 2008 before the FISA amendments acts.
In the article itself they mixed that in with other screenshots of other systems.
My guess is the way it works, is you search the metadata in XKEYSCORE and if you get hits you can analyze and then if need to go futher you need proceed to other systems. However, you need access and permissions to those other systems. If you have rights to basic XKEYSCORE searches, does not give you access to higher database or databases where content is stored.
Analysts search metadata even when they are doing 100% foreign intelligence. Again the reason is BIG DATA, you do the metadata searches to narrow down the pile of stuff to look at. If XKEYSCORE searched through content, it would take far too long. A typical signals analyst's job is something like, we caught this guy in Afghanistan planting an IED, here's the numbers in his cell phone, find his network. To get back timely information, you don't want to be overwhelmed, so at collection, full content is sent to another data and, for XKEYSCORE the metadata is extracted and fed into a database of metadata tables and these tables are what XKEYSCORE searches.