What is COBie and why it is useful in a project?

Its a format / pattern, how all data related to a facility to be produced, managed & exchanged for utilization at the right time when needed especially to support operation & maintenance teams.

There is a code of practice or the requirements can be formulated by the employer.

COBie is an information exchange specification for the life-cycle capture and delivery of information needed by facility managers. COBie can be viewed in design, construction, and maintenance software as well as in simple spreadsheets. This versatility allows COBie to be used all projects regardless of size and technological sophistication. For more information, please view this movie.