The Jedi Archives are the galaxy's greatest repository of knowledge, and Madame Jocasta Nu is their Chief Librarian. She helps other Jedi find information in the Archive using its data terminals, and she controls access to the restricted contents of its Holocron Vault. Jocasta Nu can sometimes be too confident in thinking that the Archives contain the correct answers to all questions.
A Jedi field operative needs solid information, so most Jedi Knights knew to consult the Archives prior to their missions.
When Obi-Wan Kenobi was investigating the mysterious planet Kamino, he was surprised to find no listing for it in the Jedi Archives. Jocasta did provide Obi-Wan with a brief history of Count Dooku, however.
When the Jedi militarized during the events of the Clone Wars, Jocasta Nu continued her role, but the preservation of Jedi knowledge -- and secrets -- became of utmost importance. Jedi Archive security is an important duty within the Temple, as Ahsoka Tano discovers.
The Jedi Temple Archives contained possibly the single largest source of information in the galaxy. Within the polished architecture of the Temple, incredible amounts of data were stored electronically and holographically.
Jocasta Nu's pride in the Archives and their contents sometimes blinded her to the fact that the Archives were not truly complete and could be altered from within. Thus, when Obi-Wan Kenobi searched for the planet Kamino, Jocasta Nu was of very little help. Kamino didn't show up in the records -- and according to Nu, if it didn't exist in the Archives, then it simply didn't exist.