  This paper is a survey discussing Information Retrieval concepts, methods,
and applications. It goes deep into the document and query modelling involved
in IR systems, in addition to pre-processing operations such as removing stop
words and searching by synonym techniques. The paper also tackles text
categorization along with its application in neural networks and machine
learning. Finally, the architecture of web crawlers is to be discussed shedding
the light on how internet spiders index web documents and how they allow users
to search for items on the web.
