Capacity
The concept of Capacity is available to allow for the business to limit the amount of certain categories of jobs being booked within certain time periods - thus saving some time for the booking of other categories. An obvious use case here is to ensure that, for days in the future, only 70% of time is booked for maintenance work such that 30% is kept available for booking emergency work 'on the day'.
There are various levels at which this capacity management may be applied, hence a number of tables are needed to set up the data.