Integrating life science web databases, while important and necessary, is a challenge for current integration systems mainly due to the large number of these databases, their heterogeneity and the fact that their interfaces may change often. BACIIS, a biological and chemical information integration system, is a tightly coupled federated database system that uses the mediator wrapper method in order to retrieve information from several remote web databases. BACIIS relies on a semi-automated approach for generating and maintaining wrappers in order to provide a scalable system with a limited maintenance overhead. The semi-automatic wrapper induction in BACIIS is efficient because it is based on, but not limited to a domain knowledge. Tests show that the use of ontology increases the accuracy of the wrapper induction. We also present how the wrapper induction system facilitates wrapper update, and assists in the information extraction. By using a wrapper induction system for creation and maintenance of wrappers, scalability, flexibility, and stability of the integrated information system is easily maintained.