Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Fourth Data Release of the Sloan Digital Sky Survey   This paper describes the fourth data release of the Sloan Digital Sky Survey
(SDSS), including all survey-quality data taken through June 2004. The data
release includes five-band photometric data for 180 million objects selected
over 6670 deg^2, and 673,280 spectra of galaxies, quasars, and stars selected
from 4783 deg^2 of that imaging data using the standard SDSS target selection
algorithms. These numbers represent a roughly 25% increment over those of the
Third Data Release. The Fourth Data Release also includes an additional 131,840
spectra of objects selected using a variety of alternative algorithms, to
address scientific issues ranging from the kinematics of stars in the Milky Way
thick disk to populations of faint galaxies and quasars.

31
The categories of this paper are: ao-sci
29
The categories of this paper are: funct-an
1
The categories of this paper are: cs
17
The categories of this paper are: q-fin
26
The categories of this paper are: bayes-an
34
The categories of this paper are: chem-ph
32
The categories of this paper are: atom-ph
35
The categories of this paper are: mtrl-th
5
The categories of this paper are: gr-qc
3
The categories of this paper are: physics
27
The categories of this paper are: comp-gas
20
The categories of this paper are: acc-phys
9
The categories of this paper are: nlin
37
The categories of this paper are: supr-con
16
The categories of this paper are: stat
19
The categories of this paper are: eess