A data warehouse can be described as a collection of materialised views over distributed, heterogeneous, and autonomous sources. Although most data warehouse research efforts have been focused on business-oriented decision support, many of the general principles apply to other areas. In this paper we analyse how previous work on data warehouse maintenance can be applied to the maintenance of biological data collected from web-sources. We have studied the widely used protein sequence database SWISS-PROT and the related classification database PROSITE. The results of this analysis show that these sources, although unsophisticated from a database perspective, provide a rich set of capabilities to support automatic maintenance.Moreover, the complex computations required to combine this type of data imply that incremental maintenance methods are almost always beneficial. This result contrasts some previous¯findings reported in the database literature.