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The need to search for complex and recurring patterns in database sequences is shared by many applications. In this paper, we investigate the design and optimization of a query language capable of expressing and supporting efficiently the search for complex sequential patterns in database systems. Thus, we first introduce SQL-TS, an extension of SQL to express these patterns, and then we study how to optimize the queries for this language. We take the optimal text search algorithm of Knuth, Morris and Pratt, and generalize it to handle complex queries on sequences. Our algorithm exploits the interdependencies between the elements of a pattern to minimize repeated passes over the same data. Experimental results on typical sequence queries, such as double bottom queries, confirm that substantial speedups are achieved by our new optimization techniques.

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A key advantage in the conversion from film-based to digital radiology is the possibility of a Iong-term on line electronic archival of patient studies. The popular approach based on optical disk jukeboxes for the Iong-term archive and magnetic disk storage for data caching is not economically attractive because of the cost of both the jukebox and the medium. Strategies for extending the archival system design with a tape jukebox have been studied. The proposed strategy calls for the use of high-ratio Iossy compression together with Iow-cost tape storage to make Iong-term on line archiving more affordable. An intelligent prefetching algorithm based on hospital information system and radiologic information system triggers, which in turn are augmented by manual case preparation, can effectively overcome the Ionger latency of ad hoc retrievals. This Ionger latency is caused by both system-level bottlenecks and the sequential access constraint of the tape drive. Strategies for image clustering and tape allocation by patient classification also enhance retrieval efficiency. This archival design using image compression, prefetching, and clustering could be implemented in many of the existing teleradio|ogy and picture archiving and communication systetas. T HE USE OF picture archiving and communication systems (PACS) is increasing with many leading institutions opting for large-scale installation rather than a phased modular approach. 1-7 Archival for digital radiologic data remains an unsolved problem because of slow retrieval speeds and sheer volume. Radiologists require immediate access to patient studies during clinical viewing. A medical center routinely generates a large volume of image data, which must be stored for many years depending on legal requirements and other factors. The goal of this study is to evaluate a method to extend on line archive size at lower cost and acceptable speed by the use of a slower storage device coupled with several software strategies, such as patient classification, prefetching, and compression. Intelligent image-management algorithms make possible the use of alternative tape devices that are slower but more economical than the commonly used optical disks (ODs). EXISTING PACS ARCHIVE DESIGNToday, many existing teleradiology systems and PACS rely on OD jukeboxes for long-term on-line archival, attracted by their durability, format standardization, and random accessibility. 8 The relatively slower access of the OD (because of data seek time, robotic mounting of platters into the drive, and data transfer rate) can be offset by a magnetic disk-based cache. The cache stores the most urgent (likely to be used) data in anticipation of clinical use. Aftera pre-set period of time, the data is relocated to the slower OD. This downstream data movement from a faster to a slower device is called migrationYThe data aging approach works well for recent studies. However, it does not address efficient retrieval of comparison studies. The upstream movement of data is called image caching. In radiol...