1. A computer system comprising: a non-transitory computer readable storage in which data are stored, the data including: data identifying entities described in a document, stored in computer memory, wherein the document includes a plurality of tokens appearing in an order in the document, and data defining a sequence of sentiment values assigned to the tokens in the document, the sequence of sentiment values being in the order the corresponding tokens appear in the document; and at least one processor for processing the data in the computer readable storage to assign a sentiment value to one of the identified entities in the document by: applying a filter to the sequence of sentiment values in the non-transitory computer readable storage, the filter having a width defined by a number of tokens, such that the sentiment value of a token is spread among other nearby tokens within the width of the filter, whereby each entity has contributions due to sentiment values from nearby tokens within the width of the filter, and for each entity in the document, combining the contributions from the nearby tokens to produce a sentiment value for the entity.