It works likes this: a robot wants to vists a Web site URL, say http://www.example.com/welcome.html. Before it does so, it firsts checks for http://www.example.com/robots.txt, and finds:
The “User-agent: *” means this section applies to all robots.
The “Disallow: /” tells the robot that it should not visit any pages on the site.
There are two important considerations when using /robots.txt:
- robots can ignore your /robots.txt. Especially malware robots that scan the web for security vulnerabilities, and email address harvesters used by spammers will pay no attention.
- the /robots.txt file is a publicly available file. Anyone can see what sections of your server you don’t want robots to use.
So don’t try to use /robots.txt to hide information.
Part-of-speech tagging (POS tagging or POST), also called grammatical tagging, is the process of marking up the words in a text as corresponding to a particular part of speech, based on both its definition, as well as its context—i.e., relationship with adjacent and related words in a phrase, sentence, or paragraph. A simplified form of this is commonly taught school-age children, in the identification of words as nouns, verbs, adjectives, adverbs, etc. Once performed by hand, POS tagging is now done in the context of computational linguistics, using algorithms which associate discrete terms, as well as hidden parts of speech, in accordance with a set of descriptive tags.
Phrase chunking is a natural language process that separates and segments sentences into its subconstituents, i.e. noun, verb and prepositional phrases.