XML　concurrency　control　protocol　ensures　that　transactions　execute　atomically　in　a　XML　database　system.　Existing　concurrency　control　methods　for　XML　are　mainly　based　on　locking.　In　this　paper,　we　propose　two　optimistic　concurrency　control　protocols　for　XML　that　use　snapshot-based　approach.　OptiXDOM　extends　traditional　backward-oriented　optimistic　concurrency　control　protocol　while　FOCCXDOM　is　based　on　forward-oriented　approach.　Both　protocols　are　optimized　for　XML　data　and　can　be　used　in　XML　DOM　API.　Experiments　show　that　both　OptiXDOM　and　FOCCXDOM　have　better　performance　than　that　of　lock-based　approach　when　conflicts　are　few.　Furthermore,　FOCCXDOM　has　the　larger　throughput　and　higher　abort　rate　than　that　of　OptiXDOM　in　most　cases.