Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Meaning of Null in Databases and Programming Languages   The meaning of null in relational databases is a major source of confusion
not only among database users but also among database textbook writers. The
purpose of this article is to examine what database nulls could mean and to
make some modest suggestions about how to reduce the confusion.

23
The categories of this paper are: solv-int
13
The categories of this paper are: quant-ph
19
The categories of this paper are: eess
9
The categories of this paper are: nlin
31
The categories of this paper are: ao-sci
11
The categories of this paper are: hep-lat
28
The categories of this paper are: alg-geom
37
The categories of this paper are: supr-con
18
The categories of this paper are: econ
15
The categories of this paper are: nucl-ex
34
The categories of this paper are: chem-ph
24
The categories of this paper are: dg-ga
5
The categories of this paper are: gr-qc
22
The categories of this paper are: chao-dyn
4
The categories of this paper are: cond-mat
21
The categories of this paper are: adap-org