A Comparison of the Temporal Expressiveness of Three Database Query Methods

Reference: Das, A. K. & Musen, M. A. A Comparison of the Temporal Expressiveness of Three Database Query Methods. Knowledge Systems Laboratory Medical Computer Science, June, 1995.

Abstract: Time is a multifaceted phenomenon that developers of clinical decision-support systems can model at various levels of complexity. In this paper, we examine what temporal semantics are required for querying protocol-based conditions. We analyze a set of 256 eligibility criteria that the T-Helper system uses to screen patients for enrollment in eight clinical-trial protocols for HIV disease. Since queries over large data sets are handled most efficiently at the database level, the developers of T-Helper plan to instantiate these criteria through database queries. We consider three data-manipulation methods for temporal querying -- the consensus query representation Arden Syntax, the commercial standard query language SQL, and the temporal query language TimeLineSQL (TLSQL) -- and we compare the ability of these three methods to express the eligibility criteria. 79% of the 256 criteria require operations on time stamps. We divide these temporal conditions into four patterns. The Arden Syntax can query two patterns, which represent 54% of the temporal conditions, whereas timepoint comparisons formulated in SQL can instantiate three patterns, which encompass 96% of the temporal conditions. TLSQL, which supports a temporal extension to relational databases, can express all four types of temporal patterns. Our results demonstrate that the T-Helper system requires simple temporal operations for most protocol-based queries; however, of the three approaches tested, TLSQL is the only query method that is sufficiently expressive for the protocol-based conditions in this system.

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