org.pentaho.aggdes.model

Interface StatisticsProvider

public interface StatisticsProvider

Source for statistics about a Schema. Statistics include the number of rows in the fact table, the number of distinct values of an attribute, and the number of distinct values of a set of attributes.

Method Summary

Methods

Modifier and Type	Method and Description
double	getFactRowCount() Returns the number of rows in the fact table.
double	getLoadTime(List<Attribute> attributes)
double	getRowCount(List<Attribute> attributes) Returns an estimate of the number of distinct values of a collection of attributes.
double	getSpace(List<Attribute> attributes) Returns an estimate of the amount of space (in bytes) required to store a row in an Aggregate composed of the given Attributes.

Method Detail

getFactRowCount

double getFactRowCount()

Returns the number of rows in the fact table.

Returns:

number of rows in the fact table

getRowCount

double getRowCount(List<Attribute> attributes)

Returns an estimate of the number of distinct values of a collection of attributes.

For example, we would expect getRowCount({gender}) to return 2, and getRowCount({gender, maritalStatus}) to return 4 (2 * 2).

A good implementation of this method should recognize when attributes are dependent: for example, if there are 100 suppliers in 10 cities, getRowCount({city, supplierName}) should return 100. Similarly, the amount should be bounded by the number of rows in the table which is the source of the attributes.

The algorithm may call this method many times, so a good implementation will compute statistics once only and thereafter return cached results.

Parameters:

attributes - List of attributes whose joint distribution is estimated

Returns:

Estimated number of values in the attributes' joint distribution

See Also:

getFactRowCount()

getSpace

double getSpace(List<Attribute> attributes)

Returns an estimate of the amount of space (in bytes) required to store a row in an Aggregate composed of the given Attributes.

Parameters:

attributes - List of attributes whose joint distribution is estimated

Returns:

Estimated space in bytes to store a row of attributes

getLoadTime

double getLoadTime(List<Attribute> attributes)