All of the system artifacts belong to the entire team. This allows the team to continuously move forward, avoiding bottlenecks caused by islands of knowledge in the team. This improves flow and thus productivity, and reduces the risk that work will be disrupted by staff turnover.
In order to allow all team members to share in the work, you want to avoid having very narrow specializations as much as possible. That doesn’t preclude having people with some specialization, but the team members should be Generalizing Specialists as much as possible.
Remember, though, this is just a guideline – there will always be instances where very specific specialization is required. However, in most cases Generalizing Specialists will be more productive. As Robert Heinlein said in Time Enough For Love:
A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects.