materials on an item-by-item basis means paying attention to
minute details. It is a tedious task, largely irrelevant to their
own. Accordingly, matching-problem details are selectively
abstracted away by each party so that they can focus on
problems of more direct, contractual concern to them. For
example, structural designers do not worry about vendors'
ability to deliver specialty valves or nuts-and-bolts because it is
outside of their scope of work. Pipe-spool fabricators optimize
production schedules to suit their plant's fabrication constraints
and other projects' needs. Shipping agents optimize travel by
choosing vehicles to meet delivery schedules; they package
materials to ensure that loads are stable and meet weight and
dimensional constraints during transportation. Laydown yard
personnel group materials by shipment, type, or finalinstallation
destination to ease tracking. Project managers
control progress based on percentages-of-total of materials
engineered, delivered to the site, or installed. The corresponding
planning systems must therefore allow for abstraction or detail
as needed.