Lexical chains are built according to a series of relationships between words in a text document. In the seminal work of Morris and Hirst they consider an external thesaurus (Roget's Thesaurus) as their lexical database to extract these relations. A lexical chain is formed by a sequence of words w_{1}, w_{2}, \dotsc, w_n appearing in this order, such that any two consecutive words w_i, w_{i+1} present the following properties (i.e., attributes such as category, indexes, and pointers in the lexical database):
