For some NLP applications it is important to
identify named entities NE such as person
names organization names time date or money
expressions in the text For example in informa
tion extraction systems it is crucial to identify
them in order to provide the knowledge to be
extracted and in machine translation systems
they are useful for creating translations of un
known words or for disambiguation However it
is not easy to identify these names because they
involve unknown words and hence the strategy
of listing candidates wont work Also it is some
times hard to determine the category of proper
nouns like distinguishing a person name from
a company name These phenomena are often
di erent from domain to domain One domain
may use a special pattern which is not found in
other domains