  This paper examines the difference and similarities between the two on-line
computer science citation databases DBLP and CiteSeer. The database entries in
DBLP are inserted manually while the CiteSeer entries are obtained autonomously
via a crawl of the Web and automatic processing of user submissions. CiteSeer's
autonomous citation database can be considered a form of self-selected on-line
survey. It is important to understand the limitations of such databases,
particularly when citation information is used to assess the performance of
authors, institutions and funding bodies.
  We show that the CiteSeer database contains considerably fewer single author
papers. This bias can be modeled by an exponential process with intuitive
explanation. The model permits us to predict that the DBLP database covers
approximately 24% of the entire literature of Computer Science. CiteSeer is
also biased against low-cited papers.
  Despite their difference, both databases exhibit similar and significantly
different citation distributions compared with previous analysis of the Physics
community. In both databases, we also observe that the number of authors per
paper has been increasing over time.
