Bonghee Hong

Time parameterized interval r-tree for tracing tags in RFID systems

For tracing tag locations, the trajectories should be modeled and indexed in a radio frequency identification (RFID) system. The trajectory of a tag is represented as a line that connects two spatiotemporal locations captured when the tag enters and leaves the vicinity of a reader. If a tag enters but does not leave a reader, its trajectory is represented only as a point captured at entry. Because the information that a tag stays in a reader is missing from the trajectory represented only as a point, it is impossible to find the tag that remains in a reader. To solve this problem we propose the data model in which trajectories are defined as time-parameterized intervals and new index scheme called the Time Parameterized Interval R-tree. We also propose new insert and split algorithms to enable efficient query processing. We evaluate the performance of the proposed index scheme and compare it with the R-tree and the R*-tree. Our experiments show that the new index scheme outperforms the other two in processing queries of tags on various datasets.

Dynamic Splitting Policies of the Adaptive 3DR-Tree for Indexing Continuously Moving Objects

Moving-objects databases need a spatio-temporal indexing scheme for moving objects to efficiently process queries over continuously changing locations of the objects. A simple extension of the R-tree that employs time as the third dimension of the data universe shows low space utilization and poor search performance because of overlapping index regions. In this paper, we propose a variant of the 3-dimensional R-tree called the Adaptive 3DR-tree. The dynamic splitting policies of the Adaptive 3DR-tree significantly reduce the overlap rate, and this, in turn, results in improved query performance. The results of our extensive experiments show that the Adaptive 3DR-tree outperforms the original 3D R-tree and the TB-tree typically by a big margin.

A Log-Based Cache Consistency Control of Spatial Databases in Mobile Computing Environments

In mobile client/server computing environments, mobile clients make access to their server to get interested data and then are disconnected because of high cost of wireless communication. Mobile clients usually keep their own local copies in order to reduce the overhead of communicating with the server. The updates of the server database sometimes are subject to leading to invalidation of the cached map in mobile clients. However it is not efficient to resend the entirely copied map from the server to mobile clients for solving invalidation. This paper proposes a log-based update propagation method to propagate the servers update into its corresponding mobile clients by sending only update logs. The log-based update propagation scheme raises new issues as follows. First, the continuously growing of update logs downgrades the speed of searching for the relevant log data for a specific client. Second, there is considerable overhead of transmitting the update logs into mobile clients by using wireless communication. To solve these problems, we define unnecessary logs and then suggest methods to remove the unnecessary logs.

The self-relocating index scheme for telematics GIS

The history management of vehicles is important in telematics applications. To process queries for history data, trajectories, we generally use trajectory-preserving index schemes based on the trajectory preservation property. This property means that a leaf node only contains segments belonging to a particular trajectory, regardless of the spatiotemporal locality of segments. The sacrifice of spatiotemporal locality, however, causes the index to increase the dead space of MBBs of non-leaf nodes and the overlap between the MBBs of nodes. Therefore, an index scheme for trajectories shows good performance with trajectory-based queries, but not with coordinate-based queries, such as range queries. We propose a new index scheme that improves the performance of range queries without reducing performance with trajectory-based queries. In the new index scheme using the entry relocation strategy, two entries in different nodes are exchanged to minimize the dead spaces of the MBBs of the corresponding nodes.

Indexing Moving Objects for Trajectory Retrieval on Location-Based Services

Due to the continuous growth of wireless communication technology and mobile equipment, the history management of moving object is important in a wide range of location-based applications. To process queries for history data, trajectories, we generally use trajectory-preserving index schemes based on the trajectory preservation property. This property means that a leaf node only contains segments belonging to a particular trajectory, regardless of the spatiotemporal locality of segments. The sacrifice of spatiotemporal locality, however, causes the index to increase the dead space of MBBs of non-leaf nodes and the overlap between the MBBs of nodes. Therefore, an index scheme for trajectories shows good performance with trajectory-based queries, but not with coordinate-based queries, such as range queries. We propose new index schemes that improve the performance of range queries without reducing performance with trajectory based queries.

Concurrent Updating of Large Spatial Objects

The update transactions to be executed in spatial databases have been usually known as interactive and long duration works. When a spatial object has a very large geometry of which size is larger than the screen window, it needs to concurrently update such a large spatial object for improving concurrency of updating spatial objects. Under the existing locking protocols, it is not allowed a large spatial object to be concurrently updated. We propose a partial locking scheme of allowing a transaction to set locks on parts of the large object. The partial locking scheme acquires a lock for part of the large object to allow several users to concurrently update the same object. The scheme gives benefits of improving the concurrency of updating a large object while maintaining the consistency of long duration transactions for interactively updating spatial data.

Growing node policies of a main memory index structure for moving objects databases

Recent studies on main memory index structures focus mainly on cache-conscious structures to minimize L2 cache misses; for example, in one dimensional data, CSB+-tree eliminated pointers to pack more entries in a node, and in multi-dimensional data, CR-tree compressed MBRs in order to increase utilization of the L2 cache line. Previous studies used a fixed node size that is a multiple of the cache line size. If a node overflows, it splits , regardless of the search performance. Since the time of split is determined by only the node size, the split may increase a node’s probability of being accessed. However, if the node size is not fixed, the previous case can be avoided. In this paper, we suggest a new cost model to determine whether to grow or split a node. In the cost model, we consider all relevant factors, such as cache misses, instruction counts, TLB misses, and the probability that nodes will be accessed. Use of our growing node policy has the following advantages: (i) it can have the effect of a delayed split that does not depend on the insertion order, and (ii) it can reduce the number of generated nodes and the height of the tree.

Declustering of Trajectories for Indexing of Moving Objects Databases

Efficient storage and retrieval of trajectory indexes has become an essential requirement for moving objects databases. The existing 3DR-tree is known to be an effective trajectory index structure for processing trajectory and time slice queries. Efficient processing of trajectory queries requires parallel processing based on indexes and parallel access methods for the trajectory index. Several heuristic methods have been developed to decluster R-tree nodes of spatial data over multiple disks to obtain high performance for disk accesses. However, trajectory data is different from two-dimensional spatial data because of peculiarities of the temporal dimension and the connectivity of the trajectory. In this paper, we propose a declustering policy based on spatio-temporal trajectory proximity. Extensive experiments show that our STP scheme is better than other declustering schemes by about 20%.

Design and Implementation of the Spatial Data Cache Based on Agents for Providing Mobile Map Services

Mobile clients like a PDA need a cache and a spatial index to search and access map data efficiently. When a server transmits spatial objects to a mobile client which has a low storage capacity, some of them can be duplicated in a cache of the mobile client. Moreover, the cost for strong added data in the cache and reconfiguring spatial index is very high in the mobile client with low computing power. The scheme for processing duplicated objects and disturbing tasks of the mobile client which has low computing power is needed. In this paper, we classfy the method for strorng duplicated objects and present the scheme for the both caching objects and reconfiguring a spatial index of cached objects using the clipping technique. We propose the caching system based on an agent in order to distribute the overhead of a mobile client as well as to provide efficiently map services. We design and implement it, and evaluate the performance.