As regards to the construction of SEs, this is a complex undertaking. It is
clearly a long-term effort that is (eventually) supported by commercial
companies. The SE aims to build a quantitative global repository that represents
as much information available on the Internet as possible or at least a large
amount of it. The SE maintains various data structures, to represent its
repository, like indices, directories, and catalogs. It also provides an elaborate
user interface for search purposes. The SE continuously employs various types
of robots to search out and index pages on the Internet and to dynamically
update its provided repository.