Figure 3.

Graphical representation of information searching in Entrez. A given query is divided into a series of elements: first, with respect to the logical operators, and then with respect to the space symbol. In the presented example we obtain three elements: breast, cancer and human[Organism]. Each element of the query is processed separately generating its result set. Results are merged according to the operators used in the query – first breast and cancer, and then the common part of their result sets is merged with the result set of human[Organism].