Time Range Mapping

One of the fundemenatal operations in report generation is the mapping of accounting records onto periods of time. Almost all reports will be generated for a specified reporting period and so accounting records need to be mapped onto this reporting period to generate charts and tables. In addition certain charts show evolution of values against time so records need to be mapped onto the plot-periods corresponding to the individual points of the chart. There are two basic algorithms implemented to do this depending on the level of detail required.

Basic

A single Time valued property is used to identify the position in time of the record (The CompletedTimestamp property is usually used for this). A record is mapped to a time period if the value of this property lies within the period. This is the simplest algorithm to understand and the fastest to execute but because accounting records typically represent activity that takes place over an extended period of time this algorithm can give mis-leading results when the length of the accounting record is comparible or larger than the period being mapped to.

Overlap

A pair of Time valued properties are used to identify the start and end of the accounting record and values are weighted according to the degree of overlap. There are two kinds of weighting depending on the reduction operation selected

SUM

SUM reductions should be used for cumulative properties whose value accumulates during the period of the accounting record. e.g. cost or page-faults. These values are scaled according to the fraction of the accounting record that overlaps with the reporting period.

AVG

When using the Overlap algorithm average is interpreted as average over time. AVG should be used for values that are constant over the accounting record such as number of cpus. These values are scaled according to the fraction of the reporting period the record overlaps with.