The study of indexing techniques on object oriented databases

An object-oriented database (OODB) has been becoming more important in recent years. It can deal with a large amount of complex objects and relationships that relational database (RDB) systems cannot handle well. However, the retrieval and update performance of an OODB depends on indexing techniques. In this paper, we study the indexing techniques on OODBs, based on an inheritance hierarchy and an aggregation hierarchy. Given the access probability and the size of each class, we propose a cost function to evaluate the gain of building an index on an inheritance hierarchy. For an aggregation hierarchy, we use a path-catenation technique to evaluate how to build index files on classes. Through some experiments, we found our methods have better retrieval performance than most ones proposed before.     

Dynamically adjusting MPEG4 video streams based on network bandwidth

In the paper, we try to find a method that can service more users in a video-on-demand (VoD) system, based on MPEG-4 object streams. The characteristics of object segmentation made on MPEG-4 videos can be utilized to reduce re-transmission of the same objects, and then the saved bandwidth can be used to service more users. However, some thresholds must be analyzed first to maintain the acceptable quality of services (QoS) requested by users, when reducing unnecessary object transmission on one side. Thus, according to the defined thresholds, we propose a dynamically adjusting algorithm to coordinate the object streams between the server and clients. The server not only allocates network bandwidth, but also adjusts ever-allocated QoS appropriately using a degrading and upgrading strategy, based on the current network status. Lastly, through the simulation, we found that our method has better performance than the other three methods owing to its flexibility to the network status.

Evolutionary-based feature selection approaches with new criteria for data mining: A case study of credit approval data

In this paper, the feature selection problem was formulated as a multi-objective optimization problem, and new criteria were proposed to fulfill the goal. Foremost, data were pre-processed with missing value replacement scheme, re-sampling procedure, data type transformation procedure, and min-max normalization procedure. After that a wide variety of classifiers and feature selection methods were conducted and evaluated. Finally, the paper presented comprehensive experiments to show the relative performance of the classification tasks. The experimental results revealed the success of proposed methods in credit approval data. In addition, the numeric results also provide guides in selection of feature selection methods and classifiers in the knowledge discovery process.     

Image retrieval based on AND/OR-construction models

With the rapid development of the Internet, finding desired images from numerous images has become an important research topic. In this paper, we propose an image retrieval system facilitating retrieval time and accuracy. Since the performance of image retrieval is deeply influenced by image features and retrieval methods. Five different types of features and five different methods are used to find the best combination for an image retrieval system. First, we segment out the main object in an image and then extract its features. Next, relevant features are selected from the original feature set for facilitating image retrieval, using the SAHS algorithm. Then, five methods based on AND/OR-construction are proposed to build the image retrieval model, using the relevant features. Finally, the experimental results not only show that our methods are more effective than the other state-of-the-art methods but also present some observations never explored by the previous research.

     

Fault tolerance for home agents in mobile IP

In the conventional IP protocol, whenever a mobile device moves to a different network, it must change its IP address to communicate with other nodes in the Internet. Mobile IP protocol keeps mobile nodes online without changing their IP addresses while changing the attachment points. The packets destined to mobile nodes (MN) are relayed by their home agents (HA). However, once the only one HA fails, all MNs managed by the HA will not receive packets normally. In the paper, we propose a novel protocol with multiple mobile agents (MA) where only double mobility bindings are maintained in the whole system. When an HA is failed, its backup HA can take over it in a short time without fetching the bindings from other places. Besides, we also consider the load balancing between these HAs during HA takeover and recovery. Through the simulation and analyses, we found that our method has less registration overheads, better MN-scalability, less sensitivity on MN mobility, more fault-tolerance robustness, and less takeover time than others.     

A new hybrid real-coded genetic algorithm and its application to parameters identification of soils

Inverse analysis using an optimization method based on a genetic algorithm (GA) is a useful tool for obtaining soil parameters in geotechnical fields. However, the performance of the optimization in identifying soil parameters mainly depends on the search ability of the GA used. This study aims to develop a new efficient hybrid real-coded genetic algorithm (RCGA) being applied to identify parameters of soils. In this new RCGA, a new hybrid strategy is proposed by adopting two crossovers with outstanding ability, namely the Simulated Binary Crossover and the simplex crossover. In order to increase the convergence speed, a chaotic local search technique is used conditionally. The performance of the proposed RCGA is first validated by optimizing mathematical benchmark functions. The results demonstrate that the RCGA has an outstanding search ability and faster convergence speed compared to other hybrid RCGAs. The proposed new hybrid RCGA is then further evaluated by identifying soil parameters based on both laboratory tests and field tests, for different soil models. All the comparisons demonstrate that the proposed RCGA has an excellent performance of inverse analysis in identifying soil parameters, and is thus recommended for use based on all the evaluations carried out in this paper.     

A cost-efficient and versatile sanitizing algorithm by using a greedy approach

In a very large database, there exists sensitive information that must be protected against unauthorized accesses. The confidentiality protection of the information has been a long-term goal pursued by the database security research community and the government statistical agencies. In this paper, we proposed greedy methods for hiding sensitive rules. The experimental results showed the effectiveness of our approaches in terms of undesired side effects avoided in the rule hiding process. The results also revealed that in most cases, all the sensitive rules are hidden without generating spurious rules. First, the good scalability of our approach in terms of database sizes was achieved by using an efficient data structure, FCET, to store only maximal frequent itemsets instead of storing all frequent itemsets. Furthermore, we also proposed a new framework for enforcing the privacy in mining association rules. In the framework, we combined the techniques of efficiently hiding sensitive rules with the transaction retrieval engine based on the FCET index tree. For hiding sensitive rules, the proposed greedy approach includes a greedy approximation algorithm and a greedy exhausted algorithm to sanitize the database. In particular, we presented four strategies in the sanitizing procedure and four strategies in the exposed procedure, respectively, for hiding a group of association rules characterized as sensitive or artificial rules. In addition, the exposed procedure would expose missing rules during the processing so that the number of missing rules could be lowered as much as possible.