N. Mamoulis et al. (Eds.): SSTD 2009, LNCS 5644, pp. 6–24, 2009. © Springer-Verlag Berlin Heidelberg 2009 Versioning of Network Models in a Multiuser Environment Petko Bakalov 1 , Erik Hoel 1 , Sudhakar Menon 1 , and Vassilis J. Tsotras 2 1 Environmental Systems Research Institute, Redlands, CA 92373, USA {pbakalov,ehoel,menon}@esri.com 2 University of California, Riverside, CA 92507, USA tsotras@cs.ucr.edu Abstract. The standard database mechanisms for concurrency control, which include transactions and locking protocols, do not provide the support needed for updating complex geographic data in a multiuser environment. The preferred method to resolve conflicts in GIS systems is to encapsulate the modi- fications generated by the end users through the use of multiple versions. Mul- tiuser (or versioned) geographic databases allow users to operate as though they have full access to the entire dataset. Instead of relying upon row locking, ver- sioned databases allow multiple users to simultaneously edit the same row. They implement a model for conflict detection and resolution where the first to commit the change wins by default (though clients can manually intervene and select the latter change as the winner). Network models are frequently used as a mechanism to describe the connec- tivity information between spatial features in many emerging GIS applications. Supporting networks within the context of a versioned database imposes addi- tional requirements – the complex network model must retain integrity irrespec- tive of the sequence of simultaneous edits by various clients. In this paper, we review our network model and discuss the enhancements necessary to maintain- ing topological network integrity in this complex environment. Our solution is based on the notion of dirty areas and dirty objects (i.e., regions or elements that contain edits that have not been reflected in the network connectivity index). The dirty areas and objects are identified and marked during editing of the net- work feature data. They are then subsequently cleaned as a byproduct of the in- cremental update of the connectivity network. Keywords: Versioning, Network Models, Transportation Networks. 1 Introduction Network data models have a long history as an efficient way to describe the topological connectivity information among spatial features in geographic information systems [11], [14], [17], [18]. At an abstract level, the network model can be viewed as a graph whose elements explicitly represent the connectivity information about the features in the data- base. The presence of an edge in the graph depicts the information that the two features represented by the junctions are connected and vice versa. Different versions of the