This paper describes the design and implementation of the Stanford C3
system for managing change in an environment of heterogeneous,
semistructured databases (e.g., web sites, legacy information systems
with proprietary interfaces, news feeds, etc.).  In particular, users
can (1) detect and browse changes in such databases using the TDIFF
component, (2) store and query historical data using the CORE
component, and (3) subscribe to be notified when changes of a certain
kind occur, using the QSS component.  We use wrapper and mediator
technology from the Tsimmis project to interface with diverse data
sources, and the Lore system as a store for semistructured data.  The
TDIFF component uses tree-differencing algorithms for detecting
changes in semistructured data.  The CORE component implements the
Delta-OEM (DOEM) data model and the Change Lorel (Chorel) query
language.  The QSS component ties together a variety of change
detection and change reporting mechanisms in a common framework.