Information Systems are subject to a perpetual evolution, which is particularly pressing in Web Information Systems, due to their distributed and often collaborative nature. Such continuous adaptation process, comes with a very high cost, because of the intrinsic complexity of the task and the serious ramifications of such changes upon database-centric Information System softwares. Therefore, there is a need to automate and simplify the schema evolution process and to ensure predictability and logical independence upon schema changes. Current relational technology makes it easy to change the database content or to revise the underlaying storage and indexes but does little to support logical schema evolution which nowadays remains poorly supported by commercial tools. ThePRISMsystem demonstrates a major new advance toward automating schema evolution (including query mapping and database conversion), by improving predictability, logical independence, and auditability of the process. In fact,PRISMexploits recent theoretical results on mapping composition, invertibility and query rewriting to provide DB Administrators with an intuitive, operational workbench usable in their everyday activities-thus enabling graceful schema evolution. In this demonstration, we will show (i) the functionality ofPRISMand its supportive AJAX interface, (ii) its architecture built upon a simple SQL-inspired language of Schema Modification Operators, and (iii) we will allow conference participants to directly interact with the system to test its capabilities. Finally, some of the most interesting evolution steps of popular Web Information Systems, such as Wikipedia, will be reviewed in a brief "Saga of Famous Schema Evolutions".

Schema evolution poses serious challenges in historical data management. Traditionally, historical data have been archived either by (i) migrating them into the current schema version that is well-understood by users but compromising archival quality, or (ii) by maintaining them under the original schema version in which the data was originally created, leading to perfect archival quality, but forcing users to formulate queries against complex histories of evolving schemas. In the PRIMA system, we achieve the best of both approaches, by (i) archiving historical data under the schema version under which they were originally created, and (ii) letting users express temporal queries using the current schema version. Thus, in PRIMA, the system rewrites the queries to the (potentially many) pertinent versions of the evolving schema. Moreover, the system o ers automatic documentation of the schema history, and allows the users to pose temporal queries over the metadata history itself. The proposed demonstration highlights the system features exploiting both a synthetic-educational running example and the real-life evolution histories (schemas and data), which include hundreds of schema versions from Wikipedia and Ensembl. The demonstration off ers a thorough walk-through of the system features and a hands-on system testing phase, where the audiences are invited to directly interact with the advanced query interface of PRIMA.