The inhabited planet Denobula, the homeworld of the warp-capable humanoid Denobulans, was located in this system. In 2151, while recording answers to letters from Miss Malvin's fourth grade class, Phlox introduced himself as hailing from this system. (ENT: "Breaking the Ice"; PIC: "Maps and Legends")
This system was only mentioned in dialogue.
According to Star Trek: Star Charts (pp. 36 & 44) and Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), the Denobula Triaxa (Iota Boötis) system was located in the Alpha Quadrant. This was a trinary star system with one G-class star and two F-class stars. In the 22nd century, the Denobula Triaxa system was a destination on the Denobulan, Earth, and Vulcan trade routes. This system traded with Sol (Earth), Fellebia, Neethia, Pree', Pyrithia, and Vulcan (40 Eridani A). In the late 24th century, this was a Federation system.
According to StarTrek.com, this system contained only one planet.