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| Paper: |
Methods for Structuring and Searching Very Large Catalogs |
| Volume: |
145, Astronomical Data Analysis Software and Systems VII |
| Page: |
512 |
| Authors: |
Wicenec, A. J.; Albrecht, M. |
| Abstract: |
Some existing (e.g., USNO-A1.0) and most of the upcoming catalogs (e.g., \htmladdnormallinkfoot{GSC-II}{http://pixela.stsci.edu/gsc/gsc.html} \htmladdnormallinkfoot{SDSS}{http://www-sdss.fnal.gov:8000}, \htmladdnormallinkfoot{GAIA}{http://astro.estec.esa.nl/SA- general/Projects/GAIA/}) contain data for half a billion up to several billion objects. While the usefulness of the content of these catalogs is undoubted, the feasibility of scientific research and thus the scientific value is very much dependent on the access speed to an arbitrary subset of parameters for a large number of objects. Given the data volume of such catalogs it seems impractical to build indexes for more than two or three of the parameters. One way to overcome this problem is to establish a multi-dimensional index covering the whole parameter space. This implies that the catalog is structured accordingly. The disadvantage of a multidimensional index is that the access to the main index is much slower than it would be using a dedicated structures and indexes. The most commonly used index for astronomical catalogs are the coordinates. The astrophysical importance of coordinates is limited, at least if the coordinates are not suited to the astrophysical question. However for observational purposes coordinates are the primary request key to catalogs. Here we present methods for structuring and searching very large catalogs to provide fast access to the coordinate domain of the parameter space. The principles of these methods can be extended to an arbitrary number of parameters to provide access to the whole parameter space or to another subset of the parameter space. |
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