On Analyzing the Errors in a Selectivity Estimation Method Using a Multidimensional File Structure

In this paper, estimation using we discuss the errors in selectivity the multilevel multidimensional file structure. We rst analyze the cause P rid file(MLGF), a of the estimation errors, and then investigate five factors affecting the accuracy of estimation: (1) the data distrzbution in a region, (2) the number of records stored in the MLGF, (3) the page size, (4) the query region size, and (5) the level of the MLGF directory. Next, we present through extensive experiments the tendency of estimation errors when the value The results show that the errors f o r e a c h f a c t o r chany. decrease when (1) t e dtstrtbukon of records in a rekon becomes closer to ‘the uniform one, (21 the number of reckds in the MLGF increases, (3) the pa e size decreases, (4) the query region size increases, and (5P the level of the MLGF directory containing data distribution information becomes lower. We dejiny the granule ratio, ‘the core formula renresentinq the basic relationshiv between the estimation ekor and vthe above five factors,’ and finallu examine the change of estimation errors’ in relation ‘with” the change of the granule ratio throu h that with a specific experiments. 7’he results indicate va ue for the granule ratio, errors tend H to be similar regardless of different values for the five factors.