Biologists and physicians need to access biological and medical data for their experimentations and researches. This information is available on the Internet and is scattered over many heterogeneous data sources. Collecting information is consequently tedious, time consuming and must be improved. To cope with this difficulty, our overall objective is to realize a mediator-based system to integrate heterogeneous biomedical data sources. This requires first an automatic generation of source schema, which is the goal of this work. For that, we describe an algorithm which is based on information extraction. It consists of the extraction of meta-information from each source to infer their schema. Our system enables users to access relevant and specific data, which are up-to-date. To solve the semantic heterogeneity of data sources, we are considering the creation of an ontology. Finally, the management of source evolution is discussed