DXO have a internal hiring system where openings are opened up to mindef applicants first. and if no one is interested, then it will go to public.

and yes. so when you 'plan' for your career, you can apply for that opening but its still subjected to interviews with your prospective bosses(immediate boss and maybe also his boss). If you apply for a higher 'rank' opening, as long as the bosses says ok, you can have the promotion.