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Projects using Chronus We have used Chronus in a variety of ways to support temporal queries in biomedical systems that we have developed. Temporal Constraint Language As part of out work with the Immune Tolerance Network, we are investigating the use of Chronus to execute temporal constraints in a protocol tracking application. We are using the OWL ontology language to model activities in a protocol and write temporal constraints in terms of those activities using the Semantic Web Rule Language (SWRL). Those contrains are then translated to Chronus temporal queries and executed against the underlying protocol tracking databases. Data Analysis In collaboration with researchers in the HIV Drug Resistance Database Group we are using Chronus to perform analyses of HIV treatment data [1]. These analyses involve writing Chronus queries to extract temporal patterns from the data. These patterns correspond to treatment episodes and are used to determine patient immune responses for particular drug combinations. Data Integration We have used Chronus as the underpinning of a data integration mediator in the BioSTORM [2 ] biosurveillance system. BioSTORM was a research program to develop and evaluate intelligent systems for epidemic detection and characterization. It employed a range of temporal and spatial analysis techniques for early detection of potential bioterrorist attacks. The Chronus system served as a mediator to provide a consistent format and querying mechanism for all temporal data in the system. Decision Support Chronus is being used in a hypertension advisory system called ATHENA [ 3, 4, 5, 6 ]. ATHENA has been deployed at three clinical sites in the Veterans Administration Health Care System. Chronus is used in three principal ways in ATHENA: (1) it serves as the underpinning of a conversion tool that generates a temporal database from the VA's MUMPS hierarchical database; (2) it is used by ATHENA's decision support component to perform temporal queries on this database; and (3) it is used by ATHENA's user interface component when selecting and displaying current and historical patient data. Temporal Predicate Language We are also using Chronus as a temporal predicate language in a guideline modeling system [6]. The language is used to define abstract concepts in the model. The concepts, in turn, are used to model decision-making and guideline eligibility criteria, which generate recommendations for clinical decisions and actions. Quality Assessment The QUIL project [7] for guideline-based quality assessment used Chronus to represent temporal constraints. QUIL is a language representing quality indicators that are derived from low-level plan elements and higher-level intentions in medical guidelines or performance indicators. QUIL queries consist of goal and enabling temporal constraints. Satisfying a goal constraint defines a clinical execution of the medical guideline that satisfies the quality indicator given the appropriate context defined by the enabling constraint. The target language for the goal and enabling temporal constraints is Chronus. The system compiles QUIL temporal constraints into Chronus temporal queries.