据我所知 (Jù wǒ suǒ zhī) - "As far as I know" or "To the best of my knowledge."

Example: 据我所知，他们已经开始准备了。(Jù wǒ suǒ zhī, tāmen yǐjīng kāishǐ zhǔnbèi le.) - "As far as I know, they have already started preparing."

This phrase is used to qualify the speaker's statement by indicating that it is based on their understanding or information.