Can a list of websites be considered a corpus for a particular category? I am trying to build my own corpus for particular categories such as Engineering, Business, Math, Science and etc... This will be for automatic web page categorization. Let's say I manually collect 100 websites that are related to Math. Can these 100 websites be considered a corpus for Math?
Another related question. How does this differentiate from a lexicon wherein instead of a list of websites it shows a list of words with weights such as 0 or 1 to particular categories? Example would be a sentiment lexicon with words that has weights for positive and negative. But instead of positive and negative, categories such as Math, Science are used.
 A: There may be a misunderstanding about Lexicon. Let me paraphrase Hady Elsahar, Master's Degree holder in NLP and computational linguistics

Corpus : "A corpus is a large body of natural language text used for accumulating statistics on natural language text. The plural is corpora. Corpora often include extra information such as a tag for each word indicating its part-of-speech, and perhaps the parse tree for each sentence. " 
Lexicon : "A lexicon is a collection of information about the words of a language about the lexical categories to which they belong. A lexicon is usually structured as a collection of lexical entries, like ("pig" N V ADJ). "pig" is familiar as a N, but also occurs as a verb ("Jane pigged herself on pizza") and an adjective, in the phrase "pig iron", for example. In practice, a lexical entry will include further information about the roles the word plays, such as feature information - for example, whether a verb is transitive, intransitive, ditransitive, etc., what form the verb takes (e.g. present participle, or past tense, etc.)
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I think everything is in his answer, here you will have a large body of text about math. And you will be able to know wich word refers to wich field.
