A brochure is an organizational unit, as it groups tours. Each brochure usually covers a specific season and a product type. Related brochures are grouped inside catalogs.
Brochures are essential to correctly address tours at reservation time, because tour codes could repeat across brochures. Also every departure date of every tour belonging a brochure must be between brochure's start and end dates.
Brochure's start date.
Brochure's end date.
Catalog's code to which this brochure belongs.