The Bioinformatics Web Services ontology (OBIws) is an ontology that extends the Ontology for Biomedical Investigations (OBI) to build an ontology that supports consistent annotation of bioinformatics Web services. We follow a systematic methodology for enriching OBI with terms to support Web service annotation. This process involves the design of ontology analysis diagrams for Web services and their subsequent analysis to discover terms that need to be added to the ontology. Current OBIws ontology is focusing on sequence analysis web services. With developed patterns of modeling web services, OBIws can be extended easily to support annotations of different kind web services.