An item is an individual component of an integrated system, such as a well or an injection compressor.

ARTIS ensures that the names of the items are unique. When pasting, ARTIS uses the first free alphanumerical successor for the new item names. But the item name postfix is kept the same, making it easy to copy and paste complete trains or other subsystems that have consistent tag numbering.

For an item with a positive grace period, its downtime does not reduce system capacity immediately, but only after the grace period has expired. For example:

• when an off-gas compressor has failed, we can flare the off-gas for a maximum of 3 hours before gas production needs to stop
• off-spec condensate can be sent to the off-spec tank but after 6 hours it is full
• if there is a failure of power supply, the process control system continues to run on the uninterruptible power supply for at most 24 hours.

Since the grace periods are defined on the items, they affect the diagram perspective results, not the unit perspective results. All planned and unplanned downtime events get the full grace period, even for consecutive events on the same item, component, and mode. The grace periods assume that the temporary backup is available whenever the item has a downtime event. In case of doubt, the network buffers can be used as an alternative way to model it.

An item is either on the production or the consumption side. These two sides are asymmetric; everywhere in the diagram hierarchy, the maximum capacity is relative to demand.