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<br />The Database <br /> <br />The SPWRMS database is the source for all dynamic information accessed by the <br />application. The term dynamic indicates that the information changes over time. The <br />contents of the Water Information Sheet, for example. are dynamic data. <br /> <br />The database is a series of tables which contain the data for the system. An Informix <br />database management system manages the low-level operations that keep the dala <br />intact, such as interpreting SQL commands and reading and writing data to the phys- <br />ical computer disk. The database management system aJso manages user concurrency <br />issues and provides tools for backing up the data. <br /> <br />Please refer to the SPWRMS Database Manual for information on the components of <br />the relational database. <br /> <br />Arc/lnfo Coverages <br /> <br />SPWRMS reads the binary files of several ArclInfo coverages to determine spatial <br />relationships between elements of the system. One arc coverage of the main streams <br />and rivers in the South Platte River Basin is specifically constructed so that all arcs <br />have a consistent direction (all arcs point upstream). The application reads this <br />coverage to create the in-memory representation of the river system. Two point cover- <br />ages provide the points of interest managed by SPWRMS-one for stream gauges <br />and one for diversion structures. These points are referenced to nodes in the network <br />coverage by means of an ArclInfo 10. SPWRMS uses the 10 to place the structures <br />and gauges on the graph. The ArclInfo coverages are never accessed after system <br />initialization. <br /> <br />See the "Initialization" section on page 12 for a description of how these coverages <br />are used to initialize the in-memory graph. Refer to the SPWRMS Database Manual <br />for a full description of these coverages and maintenance information. <br /> <br />In-Memory Network Graph <br /> <br />Most data used by SWPRMS during program execution is loaded into an in-memory <br />network graph on program start-up. This network graph provides the connection <br />between spatial information (topology) from ArclInfo coverages and the relational <br />data slored in the Informix database. The graph is created by reading the Arc/Info <br />binary file for the stream network coverage and then filled in with relevant relational <br />data. <br /> <br />Whenever possible, dala is retrieved from the in-memory network graph instead of <br />from the database. Reading data from the hardware disk, the result of a query to the <br />database, is at least two orders of magnitude slower than reading from memory. Data- <br />base queries are even slower because the DBMS must first locale the dala prior to <br />reading. <br /> <br />Data derived from relational database and stored in memory is available for faster <br />access through the in-memory network graph. For example, the current use list-the <br />liSl of water rights currently available at a structure-is derived from the database <br /> <br />6 <br />