Data processing. The figure shows the order of the different steps. First the user selects his articles and then the data processing is triggered. The web tool asks the PubMed utilities (Entrez Programming Utilities, http://eutils.ncbi.nlm.nih.gov/entrez/query/static/eutils_help.html) to retrieve the ISSN. With this item the Horizon system is queried. If the journal is available, the system is called again to find out if an ejournal entry is set. With all this information a results page is generated in a last step.