In addition to a record name, each record is allocated a position in level number (or PIL number) which defines its location in its parents sub-tree. PIL numbers are integers greater than zero. Although the children of an upper level record do not have to have contiguous PIL numbers, each child of an upper level record must have a unique PIL number. PIL numbers can be, and usually are, repeated for the children of different upper level records, particularly when the upper level records are siblings.

PIL numbers can be used as an alternative to record names. They are not as meaningful, but as they are numeric they are therefore useful in mathematical statements within XCM.

Record names are often based on numeric values such as level RL's, strip numbers or centroid co-ordinates. In these situations it is common to use a record's position in level number as its record name (in string format).

It is often useful for related records in different sub-branches of the hierarchy to have the same PIL numbers. Consider a multi-seam open cut coal deposit where the lowest level in the hierarchy is seam. Only a sub-set of the seams would occur in each strip and this sub-set varies across the deposit and hence across the database. It is useful to allocate a particular position in level (PIL) number to each seam and to only create a record with that PIL number if the seam occurs within the strip. This is a useful mechanism for highlighting where seams are missing across the deposit.

Geological packages generally identify the seam by it's name, and if a suitable numeric value cannot be generated from a look-up table, XPAC must assign PIL numbers for each record during the import process. If left unconstrained, XPAC will create the records with sequential PIL numbers according to the order in which the data is imported. This will normally result in the same seam having different PIL numbers in different strips and may even result in the seams not appearing in stratigraphic order.

To avoid this, it is recommended that PIL numbers be set up (in a position table) to cover all seams which may occur in the database, in a logical order. The position table for the relevant level of the database must be activated before the records are imported. The position table allows a unique number to be allocated to every possible seam name and ensures this number is used as the record's seam PIL number during the import process.

Click here for further details on setting up a position table for a level.