Architecture for large-scale automatic web accessibility evaluation based on the UWEM methodology

The European Internet Accessibility project (EIAO) has developed an Observatory for performing large scale automatic web accessibility evaluations of public sector web sites in Europe. The architecture includes a distributed web crawler that crawls web sites for links until either a given budget of web pages have been identified or the web site has been crawled exhaustively. Subsequently, a uniform random subset of the crawled web pages is sampled and sent for accessibility evaluation and the evaluation results are stored in a Resource Description Format (RDF) database that is later loaded into the EIAO data warehouse using an Extract-Transform-Load (ETL) tool. The aggregated indicator results in the data warehouse are finally presented in a Plone based online reporting tool. This paper describes the final version of the EIAO architecture and outlines some of the technical and architectural challenges that the project faced and the solutions developed towards building a system capable of regular large-scale accessibility evaluations with sufficient capacity and stability. It also outlines some possible future architectural improvements.