Dependency rules

The stockpiles dependency rules control how the records used to model the stockpile are organised and how they become available when the stockpile is depleted. There are two parameters used to define the stockpile dependency rules and they are described below.

dependency rules for stockpiles

Pile Type (parcel)

Use the Pile Type (parcel) list box to define the behaviour of each pile. The following settings are available.

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The Average setting indicates that all material moved to a stockpile should be merged into a single record. When each parcel of material is moved to the stockpile, its contents are combined with the material from other parcels already moved to the pile. In effect a running total is maintained for every field in the database.

When the pile has been completed, the running total is stored in a pile record on level 2 of the database, under the stockpiles parent record. There is no way within the stockpile records to track the individual movements of material to the stockpile as they have all been merged into the same record, however the output path of the resource(s) that built the stockpile can be used to do this.

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The First In First Out (FIFO) setting indicates that every parcel of material moved to the stockpile (every scheduling step with this stockpile as its destination) must be created as a separate record. This allows each parcel to be depleted independently of the others.

To model this, a pile record is still created under the stockpile parent record. But a series of parcel records are also created under the pile record (on level 3 of the database). Furthermore, when each parcel is added to the database, a dependency is created with this parcel as the successor and the previous parcel as the predecessor. This ensures the first parcel in the pile is mined first, followed by the second and so on.

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The Last in First Out (LIFO) setting indicates the parcels within each pile should be modelled in the same way as for FIFO stockpiles, but the dependency chain is created in the opposite direction (the next parcel is the predecessor). The records are created in exactly the same way, but the last parcel will be mined first, followed by the penultimate, and so on.

•	The Unrestricted setting again indicates that each pile must be modelled in exactly the same way as FIFO stockpiles, with a level 3 record for each individual parcel. But in this case, no dependencies are created whatsoever, allowing the parcels to be mined in any order.

When you select the Average setting as the Pile Type for a stockpile, XPAC will require a moderate number of records. But, when you select any of the other pile type options, the number of records needed to model the stockpile can become very large, especially if each step is very small. Take care to ensure the maximum increment settings of resources mining to these types of stockpiles are reasonable.

Between Piles

Use the Between Piles list box to define the order in which each pile must be mined. Two settings are available as follows.

•	The Unrestricted setting is the most common and is used to indicate that once a pile has been created, it will be immediately available for mining. If multiple piles are created, they can be depleted in any order.

•	The First In First Out setting is used to indicate that once a pile has been created it cannot be scheduled unless the previous pile has been fully depleted. This is achieved by creating dependencies between each pile record, with the previous pile as the predecessor.