5. A non-transitory machine-readable storage medium comprising a set of instructions which, when executed by one or more processors of a machine, cause the machine to perform operations comprising: estimating, for each token in a set of tokens in a description, a probability that the token is irrelevant; associating, with each token in the set of tokens in the description, one of a first value, a second value, or a third value, based on whether, respectively, the token occurs in a header of the description, a lexical association exists between the token and a token in the header, or the lexical association is absent and the token does not occur in the header; iterating over a plurality of groups of sequential tokens in the description, in each iteration, selecting a group, computing a relevance value of the selected group based, at least in part, on at least one estimated probability of one or more tokens outside the selected group and on values associated with one or more tokens in the selected group; and indicating one of the plurality of groups as having a greatest relevance value.
5. A non-transitory machine-readable storage medium comprising a set of instructions which, when executed by one or more processors of a machine, cause the machine to perform operations comprising: estimating, for each token in a set of tokens in a description, a probability that the token is irrelevant; associating, with each token in the set of tokens in the description, one of a first value, a second value, or a third value, based on whether, respectively, the token occurs in a header of the description, a lexical association exists between the token and a token in the header, or the lexical association is absent and the token does not occur in the header; iterating over a plurality of groups of sequential tokens in the description, in each iteration, selecting a group, computing a relevance value of the selected group based, at least in part, on at least one estimated probability of one or more tokens outside the selected group and on values associated with one or more tokens in the selected group; and indicating one of the plurality of groups as having a greatest relevance value. 6. The machine-readable storage medium of claim 5 , wherein the description corresponds to one of an abstract item and a concrete item.