A Map Document Model for High Efficiency Editing Transaction.
ISBN 978-85-88783-11-9
Authors
1Liesong, H.; 2Chuncheng, Y.
1XI'AN RESEARCH INSTITUTE OF SURVEYING AND MAPPING Email: bealiouve@163.com
2XI'AN RESEARCH INSTITUTE OF SURVEYING AND MAPPING Email: ycc_3000_vip_ycc@163.com
Abstract
Geographical environment is constantly changing with human activities, the demand for higher verisimilitude digital maps and geographic information services is growing rapidly. Most of the mapping time is used to process data or edit map during data acquisition and compilation of maps. Map editing becomes a hard work and repeated digital work. Collaborative mapping and long transaction processing based on geodatabase can meet the need to keep geometry data consistency. But the transactions based on database such as execution, submission and rollback are completed by DBMS. Those operations are not completed instantaneously, even a short transaction will take a few seconds to execute. Long transaction which may contain multiple sub transaction, nested transaction or circular transaction is more complex in database. Its execution time is equal to the time all atomic transactions which composed of the long transaction execution plus the compensation time of the failure transactions. This time may be as long as a few days or weeks. So the DBMS transaction execution efficiency becomes the restriction of collaborative map editing efficiency. In fact, because the change of any state in a computer can be described as a transaction, geographical object state change in map document also can be described as map editing transaction. The relative document state changes can be quickly completed by the program. A single map document data size is usually small. Sharing this map document of rapid transaction is possible. Programming to simulate the map editing transaction or long transaction, can not only acquire very high efficiency, but also the simulation operation itself is freer to handle, unlikely in DBMS the DDL operations are limited. True ACID transaction is difficult to achieve.The process programming is difficult to be compatible with the current object oriented programming technology. Some other methods simulate transaction but lost free transaction controls.To overcome these shortcomings, Some Researchers proposed structured exception handling (SEH) and virtual memory protection (VMP) to realize the redo/undo. The method is an "original data" plus "increment data of state change” method. This method has several advantages which are concluded in the paper. Therefore, SEH and VMP technology is an ideal method to modeling map editing transaction. Modeling with fixed data length object is very simple, but the document modeling of variable length data is complicated, especially the map document contains a variety of complex objects such as layer, features. Therefore, extended modeling should base on the characteristics of spatial data. A general map document model is described in this paper. The map document contains a list of layers, used to manage the geographic layers. The layer contains feature list, to manage the geographical features. The feature contains attribute list, point array and relationship list. The attribute list contains the name, grade, and other different attribute values. Point array saves geographical coordinates of features. The relationship list manages spatial relationships between different features. The variables definitions and editing transaction definitions in map document model are formed. Map editing transaction execution and management are also designed. Twenty pieces of 1:5 million scale map data were selected for experiments. These experiments took place in an ordinary PC. Through these experiments, the editing transaction support map document model and its management mechanism makes GIS programming easy without considering all DBMS’s transaction usage limitation. Map editing transactions ACID characters can be strictly maintained and be high efficiently executed. Based on the above model, developers and users can customize the long transaction which can be used in collaborative mapping network.
Keywords
editing transaction; collaborative mapping; map document