PEACE-Ful Web Event Extraction and Processing as Bitemporal Mutable Events.

The web is the largest bulletin board of the world. Events of all types, from flight arrivals to business meetings, are announced on this board. Tracking and reacting to such event announcements, however, is a tedious manual task, only slightly alleviated by email or similar notifications. Announcements are published with human readers in mind, and updates or delayed announcements are frequent. These characteristics have hampered attempts at automatic tracking. PEACE provides the first integrated framework for event processing on top of web event ads, consisting of event extraction, complex event processing, and action execution in response to these events. Given a schema of the events to be tracked, the framework populates this schema by extracting events from announcement sources. This extraction is performed by little programs called wrappers that produce the events including updates and retractions. PEACE then queries these events to detect complex events, often combining announcements from multiple sources. To deal with updates and delayed announcements, PEACE's schemas are bitemporal, to distinguish between occurrence and detection time. This allows complex event specifications to track updates and to react upon differences in occurrence and detection time. In case of new, changing, or deleted events, PEACE allows one to execute actions, such as tweeting or sending out email notifications. Actions are typically specified as web interactions, for example, to fill and submit a form with attributes of the triggering event. Our evaluation shows that PEACE's processing is dominated by the time needed for accessing the web to extract events and perform actions, allotting to 97.4%. Thus, PEACE requires only 2.6% overhead, and therefore, the complex event processor scales well even withmoderate resources. We further show that simple and reasonable restrictions on complex event specifications and the timing of constituent events suffice to guarantee that PEACE only requires a constant buffer to process arbitrarily many event announcements. [ABSTRACT FROM AUTHOR]