Learning classifiers from distributed, semantically heterogeneous, autonomous data sources

Recent advances in computing, communications, and digital storage technologies, together with development of high throughput data acquisition technologies have made it possible to gather and store large volumes of data in digital form. These developments have resulted in unprecedented opportunities for large-scale data-driven knowledge acquisition with the potential for fundamental gains in scientific understanding (e.g., characterization of macromolecular structure-function relationships in biology) in many data-rich domains. In such applications, the data sources of interest are typically physically distributed, semantically heterogeneous and autonomously owned and operated, which makes it impossible to use traditional machine learning algorithms for knowledge acquisition. However, we observe that most of the learning algorithms use only certain statistics computed from data in the process of generating the hypothesis that they output and we use this observation to design a general strategy for transforming traditional algorithms for learning from data into algorithms for learning from distributed data. The resulting algorithms are provably exact in that the classifiers produced by them are identical to those obtained by the corresponding algorithms in the centralized setting (i.e., when all of the data is available in a central location) and they compare favorably to their centralized counterparts in terms of time and communication complexity. To deal with the semantical heterogeneity problem, we introduce ontology-extended data sources and define a user perspective consisting of an ontology and a set of interoperation constraints between data source ontologies and the user ontology. We show how these constraints can be used to define mappings and conversion functions needed to answer statistical queries from semantically heterogeneous data viewed from a certain user perspective. That is further used to extend our approach for learning from distributed data into a theoretically sound approach to learning from semantically heterogeneous data. The work described above contributed to the design and implementation of AirlDM, a collection of data source independent machine learning algorithms through the means of sufficient statistics and data source wrappers, and to the design of INDUS, a federated, query-centric system for knowledge acquisition from distributed, semantically heterogeneous, autonomous data sources.

[1]  Kagan Tumer,et al.  Robust Order Statistics Based Ensembles for Distributed Data Mining , 2001 .

[2]  Donato Malerba,et al.  A Comparative Analysis of Methods for Pruning Decision Trees , 1997, IEEE Trans. Pattern Anal. Mach. Intell..

[3]  John A. Keane,et al.  Data Allocation Algorithm for Parallel Association Rule Discovery , 2001, PAKDD.

[4]  O. Mangasarian,et al.  Massive data discrimination via linear support vector machines , 2000 .

[5]  Thomas G. Dietterich What is machine learning? , 2020, Archives of Disease in Childhood.

[6]  Vasant Honavar,et al.  A two-stage classifier for identification of protein-protein interface residues , 2004, ISMB/ECCB.

[7]  Luc De Raedt,et al.  Relational Knowledge Discovery in Databases , 1996, Inductive Logic Programming Workshop.

[8]  James S. Harris,et al.  Tables of integrals , 1998 .

[9]  Corinna Cortes,et al.  Support-Vector Networks , 1995, Machine Learning.

[10]  Philip A. Bernstein,et al.  Applying Model Management to Classical Meta Data Problems , 2003, CIDR.

[11]  Rong Chen,et al.  A new algorithm for learning parameters of a Bayesian network from distributed data , 2002, 2002 IEEE International Conference on Data Mining, 2002. Proceedings..

[12]  Sung Wook Baik,et al.  Application of a distributed data mining approach to network intrusion detection , 2002, AAMAS '02.

[13]  Vasant Honavar,et al.  Information extraction and integration from heterogeneous, distributed, autonomous information sources - a federated ontology-driven query-centric approach , 2003, Proceedings Fifth IEEE Workshop on Mobile Computing Systems and Applications.

[14]  Salvatore J. Stolfo,et al.  JAM: Java Agents for Meta-Learning over Distributed Databases , 1997, KDD.

[15]  Jian Xu,et al.  Using Ontologies to Integrate Domain Specific Data Sources , 2001, IRI.

[16]  Rong Chen,et al.  Collective Mining of Bayesian Networks from Distributed Heterogeneous Data , 2004, Knowl. Inf. Syst..

[17]  Wenliang Du,et al.  Building decision tree classifier on private data , 2002 .

[18]  Alon Y. Levy Logic-based techniques in data integration , 2001 .

[19]  Salvatore J. Stolfo,et al.  Distributed data mining in credit card fraud detection , 1999, IEEE Intell. Syst..

[20]  Michalis Petrakos,et al.  A Statistical Metadata Model for Simultaneous Manipulation of both Data and Metadata , 2004, Journal of Intelligent Information Systems.

[21]  Lawrence B. Holder,et al.  Graph-Based Data Mining , 2000, IEEE Intell. Syst..

[22]  Nagiza F. Samatova,et al.  RACHET: An Efficient Cover-Based Merging of Clustering Hierarchies from Distributed Datasets , 2002, Distributed and Parallel Databases.

[23]  Andrew W. Moore,et al.  Cached Sufficient Statistics for Efficient Machine Learning with Large Datasets , 1998, J. Artif. Intell. Res..

[24]  Vasant Honavar,et al.  Distributed knowledge networks , 1998, 1998 IEEE Information Technology Conference, Information Environment for the Future (Cat. No.98EX228).

[25]  Michael Wooldridge,et al.  Agent-Oriented Software Engineering , 1999, ATAL.

[26]  Finn V. Jensen,et al.  Bayesian Networks and Decision Graphs , 2001, Statistics for Engineering and Information Science.

[27]  Val Tannen,et al.  K2/Kleisli and GUS: Experiments in integrated access to genomic data sources , 2001, IBM Syst. J..

[28]  H. Hahn Sur quelques points du calcul fonctionnel , 1908 .

[29]  Rong Chen,et al.  Learning Bayesian Network Structure from Distributed Data , 2003, SDM.

[30]  Judea Pearl,et al.  Graphical Models for Probabilistic and Causal Reasoning , 1997, The Computer Science and Engineering Handbook.

[31]  Peter Haddawy,et al.  Answering Queries from Context-Sensitive Probabilistic Knowledge Bases (cid:3) , 1996 .

[32]  Philippe Bonnet,et al.  Towards Sensor Database Systems , 2001, Mobile Data Management.

[33]  Shonali Krishnaswamy,et al.  Techniques for Estimating the Computation and Communication Costs of Distributed Data Mining , 2002, International Conference on Computational Science.

[34]  Vasant Honavar,et al.  Ontology Language Extensions to Support Localized Semantics, Modular Reasoning, and Collaborative Ontology Design and Ontology Reuse , 2004 .

[35]  KantarciogluMurat,et al.  Privacy-Preserving Distributed Mining of Association Rules on Horizontally Partitioned Data , 2004 .

[36]  I. S. Gradshteyn,et al.  Table of Integrals, Series, and Products , 1976 .

[37]  Geoffrey E. Hinton,et al.  A general framework for parallel distributed processing , 1986 .

[38]  Lawrence B. Holder,et al.  Graph-Based Relational Concept Learning , 2002, International Conference on Machine Learning.

[39]  Vasant Honavar,et al.  Learning Decision Trees from Multi-Relational Data , 2003 .

[40]  J. Ross Quinlan,et al.  Induction of Decision Trees , 1986, Machine Learning.

[41]  Yike Guo,et al.  Parallel Methods for Scaling Data Mining Algorithms to Large Data Sets , 2001 .

[42]  Thorsten Joachims,et al.  Making large-scale support vector machine learning practical , 1999 .

[43]  James Hendler,et al.  Science and the Semantic Web , 2003, Science.

[44]  M. Fréchet Sur quelques points du calcul fonctionnel , 1906 .

[45]  B. Ripley,et al.  Pattern Recognition , 1968, Nature.

[46]  Kevin Chen-Chuan Chang,et al.  Mind your vocabulary: query mapping across heterogeneous information sources , 1999, SIGMOD '99.

[47]  Yoav Freund,et al.  Large Margin Classification Using the Perceptron Algorithm , 1998, COLT.

[48]  Vasant Honavar,et al.  Decision Tree Induction from Distributed Heterogeneous Autonomous Data Sources , 2003 .

[49]  Jennifer Widom,et al.  The TSIMMIS Approach to Mediation: Data Models and Languages , 1997, Journal of Intelligent Information Systems.

[50]  Hillol Kargupta,et al.  Distributed Clustering Using Collective Principal Component Analysis , 2001, Knowledge and Information Systems.

[51]  Leo Breiman,et al.  Classification and Regression Trees , 1984 .

[52]  Ron Kohavi,et al.  Scaling Up the Accuracy of Naive-Bayes Classifiers: A Decision-Tree Hybrid , 1996, KDD.

[53]  Michael R. Genesereth,et al.  The Conceptual Basis for Mediation Services , 1997, IEEE Expert.

[54]  Philip S. Yu,et al.  Efficient parallel data mining for association rules , 1995, CIKM '95.

[55]  Nello Cristianini,et al.  The Kernel-Adatron : A fast and simple learning procedure for support vector machines , 1998, ICML 1998.

[56]  Luc De Raedt,et al.  Bayesian Logic Programs , 2001, ILP Work-in-progress reports.

[57]  Vasant Honavar,et al.  Learning decision tree classifiers from attribute value taxonomies and partially specified data , 2003, ICML 2003.

[58]  Yiming Yang,et al.  Modified Logistic Regression: An Approximation to SVM and Its Applications in Large-Scale Text Categorization , 2003, ICML.

[59]  Vipin Kumar,et al.  Parallel Formulations of Decision-Tree Classification Algorithms , 2004, Data Mining and Knowledge Discovery.

[60]  John K. Debenham A Negotiation Agent , 2004, Australian Conference on Artificial Intelligence.

[61]  Rüdiger Wirth,et al.  When Distribution is Part of the Semantics: A New Problem Class for Distributed Knowledge Discovery , 2001 .

[62]  Chris Clifton,et al.  Privacy-preserving clustering with distributed EM mixture modeling , 2004, Knowledge and Information Systems.

[63]  Vladimir Vapnik,et al.  Statistical learning theory , 1998 .

[64]  R. Darlington,et al.  Regression and Linear Models , 1990 .

[65]  Johannes Gehrke,et al.  BOAT—optimistic decision tree construction , 1999, SIGMOD '99.

[66]  Richard R. Muntz,et al.  Scalable Exploratory Data Mining of Distributed Geoscientific Data , 1996, KDD.

[67]  Chris Clifton,et al.  Privacy-preserving distributed mining of association rules on horizontally partitioned data , 2004, IEEE Transactions on Knowledge and Data Engineering.

[68]  Craig A. Knoblock,et al.  Retrieving and Integrating Data from Multiple Information Sources , 1993, Int. J. Cooperative Inf. Syst..

[69]  Hendrik Blockeel,et al.  Multi-Relational Data Mining , 2005, Frontiers in Artificial Intelligence and Applications.

[70]  Mohammed J. Zaki Parallel and distributed association mining: a survey , 1999, IEEE Concurr..

[71]  Shonali Krishnaswamy,et al.  Internet Delivery of Distributed Data Mining Services: Architectures, Issues and Prospects , 2003 .

[72]  Vasant Honavar,et al.  Generation of Attribute Value Taxonomies from Data and Their Use in Data-Driven Construction of Accurate and Compact Naive Bayes Classifiers , 2004 .

[73]  Manfred Jaeger,et al.  Relational Bayesian Networks , 1997, UAI.

[74]  Hillol Kargupta,et al.  Constructing Simpler Decision Trees from Ensemble Models Using Fourier Analysis , 2002, DMKD.

[75]  Steven Skiena,et al.  The Algorithm Design Manual , 2020, Texts in Computer Science.

[76]  I. Hamzaoglu H. Kargupta,et al.  Distributed Data Mining Using An Agent Based Architecture , 1997, KDD 1997.

[77]  Gu Si-yang,et al.  Privacy preserving association rule mining in vertically partitioned data , 2006 .

[78]  E. Polak Introduction to linear and nonlinear programming , 1973 .

[79]  Anthony Rowe,et al.  InfoGrid: providing information integration for knowledge discovery , 2003, Inf. Sci..

[80]  Rakesh Agrawal,et al.  SPRINT: A Scalable Parallel Classifier for Data Mining , 1996, VLDB.

[81]  Inderjit S. Dhillon,et al.  A Data-Clustering Algorithm on Distributed Memory Multiprocessors , 1999, Large-Scale Parallel Data Mining.

[82]  Carla E. Brodley,et al.  Random Projection for High Dimensional Data Clustering: A Cluster Ensemble Approach , 2003, ICML.

[83]  Stefan Rüping,et al.  Incremental Learning with Support Vector Machines , 2001, ICDM.

[84]  Domenico Talia,et al.  Scalable Parallel Clustering for Data Mining on Multicomputers , 2000, IPDPS Workshops.

[85]  Sally I. McClean,et al.  A negotiation agent for distributed heterogeneous statistical databases , 2002, Proceedings 14th International Conference on Scientific and Statistical Database Management.

[86]  Lawrence O. Hall,et al.  Comparing pure parallel ensemble creation techniques against bagging , 2003, Third IEEE International Conference on Data Mining.

[87]  James A. Hendler,et al.  The Semantic Web" in Scientific American , 2001 .

[88]  Mark A. Musen,et al.  Modern architectures for intelligent systems: reusable ontologies and problem-solving methods , 1998, AMIA.

[89]  Michael Stonebraker,et al.  Predicate migration: optimizing queries with expensive predicates , 1992, SIGMOD Conference.

[90]  Thomas G. Dietterich Multiple Classifier Systems , 2000, Lecture Notes in Computer Science.

[91]  Catherine Blake,et al.  UCI Repository of machine learning databases , 1998 .

[92]  R. Connelly In Handbook of Convex Geometry , 1993 .

[93]  Ran Wolff,et al.  A high-performance distributed algorithm for mining association rules , 2004, Knowledge and Information Systems.

[94]  Craig A. Knoblock,et al.  The Ariadne Approach to Web-Based Information Integration , 2001, Int. J. Cooperative Inf. Syst..

[95]  Chris Clifton,et al.  Tools for privacy preserving distributed data mining , 2002, SKDD.

[96]  JOHANNES GEHRKE,et al.  RainForest—A Framework for Fast Decision Tree Construction of Large Datasets , 1998, Data Mining and Knowledge Discovery.

[97]  Rakesh Agrawal,et al.  Parallel Mining of Association Rules , 1996, IEEE Trans. Knowl. Data Eng..

[98]  Jaideep Vaidya,et al.  Privacy preserving association rule mining in vertically partitioned data , 2002, KDD.

[99]  Bernhard Schölkopf,et al.  Support vector learning , 1997 .

[100]  Vladimir Vapnik,et al.  Chervonenkis: On the uniform convergence of relative frequencies of events to their probabilities , 1971 .

[101]  W. Pitts,et al.  A Logical Calculus of the Ideas Immanent in Nervous Activity (1943) , 2021, Ideas That Created the Future.

[102]  Mario Cannataro,et al.  KNOWLEDGE GRID: High Performance Knowledge Discovery on the Grid , 2001, GRID.

[103]  Yishay Mansour,et al.  Learning Boolean Functions via the Fourier Transform , 1994 .

[104]  Ian H. Witten,et al.  Data mining: practical machine learning tools and techniques with Java implementations , 2002, SGMD.

[105]  Lise Getoor,et al.  Learning Probabilistic Relational Models , 1999, IJCAI.

[106]  Vasant Honavar,et al.  Discovering Protein Function Classification Rules from Reduced Alphabet Representations of Protein Sequences , 2002, JCIS.

[107]  James A. Larson,et al.  Federated databases: architectures and issues , 1990 .

[108]  Thure Etzold,et al.  SRS: An Integration Platform for Databanks and Analysis Tools in Bioinformatics , 2003, Bioinformatics.

[109]  V. S. Subrahmanian,et al.  An ontology-extended relational algebra , 2003, Proceedings Fifth IEEE Workshop on Mobile Computing Systems and Applications.

[110]  Dustin Boswell,et al.  Introduction to Support Vector Machines , 2002 .

[111]  Vasant Honavar,et al.  A Framework for Learning from Distributed Data Using Sufficient Statistics and Its Application to Learning Decision Trees , 2004, Int. J. Hybrid Intell. Syst..

[112]  Joel H. Saltz,et al.  Decision Tree Construction for Data Mining on Cluster of Shared-Memory Multiprocessors , 2001 .

[113]  Patrick Valduriez,et al.  Scaling heterogeneous databases and the design of Disco , 1996, Proceedings of 16th International Conference on Distributed Computing Systems.

[114]  Barbara A. Eckman,et al.  A Practitioner's Guide to Data Management and Data Integration in Bioinformatics , 2003, Bioinformatics.

[115]  Gerhard Weiß,et al.  A multiagent perspective of parallel and distributed machine learning , 1998, AGENTS '98.

[116]  Robert L. Grossman,et al.  A Framework for Finding Distributed Data Mining Strategies That are Intermediate Between Centralized , 2000 .

[117]  Srinivasan Parthasarathy,et al.  Parallel Data Mining for Association Rules on Shared-memory Systems , 1998 .

[118]  Leslie G. Valiant,et al.  A theory of the learnable , 1984, STOC '84.

[119]  Marvin Minsky,et al.  Perceptrons: An Introduction to Computational Geometry , 1969 .

[120]  Ruoming Jin,et al.  Communication and Memory Efficient Parallel Decision Tree Construction , 2003, SDM.

[121]  Lei Liu,et al.  MobiMine: monitoring the stock market from a PDA , 2002, SKDD.

[122]  Chris Clifton,et al.  Privacy-preserving k-means clustering over vertically partitioned data , 2003, KDD '03.

[123]  Guido Moerkotte,et al.  Efficient maintenance of materialized mediated views , 1995, SIGMOD '95.

[124]  Chuleerat Jaruskulchai,et al.  A parallel learning algorithm for text classification , 2002, KDD.

[125]  Raj Bhatnagar,et al.  Pattern Discovery in Distributed Databases , 1997, AAAI/IAAI.

[126]  Philip S. Yu,et al.  Distributed data mining in a chain store database of short transactions , 2002, KDD.

[127]  Emden R. Gansner,et al.  An open graph visualization system and its applications to software engineering , 2000 .

[128]  Claudio Gentile,et al.  On the generalization ability of on-line learning algorithms , 2001, IEEE Transactions on Information Theory.

[129]  Richard Fikes,et al.  The Ontolingua Server: a tool for collaborative ontology construction , 1997, Int. J. Hum. Comput. Stud..

[130]  Yike Guo,et al.  An Architecture for Distributed Enterprise Data Mining , 1999, HPCN Europe.

[131]  Vasant Honavar,et al.  Learning Naive Bayes Classifiers From Attribute Value Taxonomies and Partially Specified Data , 2004 .

[132]  J. Davenport Editor , 1960 .

[133]  Kate Smith-Miles,et al.  A Data Mining Architecture for Distributed Environments , 2002, IICS.

[134]  F ROSENBLATT,et al.  The perceptron: a probabilistic model for information storage and organization in the brain. , 1958, Psychological review.

[135]  James A. Hendler,et al.  Dynamic Ontologies on the Web , 2000, AAAI/IAAI.

[136]  Peter E. Hart,et al.  Nearest neighbor pattern classification , 1967, IEEE Trans. Inf. Theory.

[137]  Mario Cannataro,et al.  The knowledge grid , 2003, CACM.

[138]  Philip A. Bernstein,et al.  A vision for management of complex models , 2000, SGMD.

[139]  Subbarao Kambhampati,et al.  Optimizing Recursive Information-Gathering Plans , 1999, IJCAI.

[140]  Maozhen Li,et al.  PaDDMAS: parallel and distributed data mining application suite , 2000, Proceedings 14th International Parallel and Distributed Processing Symposium. IPDPS 2000.

[141]  Joydeep Ghosh,et al.  Privacy-preserving distributed clustering using generative models , 2003, Third IEEE International Conference on Data Mining.

[142]  Foster J. Provost,et al.  Scaling Up: Distributed Machine Learning with Cooperation , 1996, AAAI/IAAI, Vol. 1.

[143]  Kotagiri Ramamohanarao,et al.  Learning to Share Distributed Probabilistic Beliefs , 2002, ICML.

[144]  A. Hanks Canada , 2002 .

[145]  Nick Roussopoulos,et al.  MOCHA: a self-extensible database middleware system for distributed data sources , 2000, SIGMOD '00.

[146]  Surajit Chaudhuri,et al.  On the Efficient Gathering of Sufficient Statistics for Classification from Large SQL Databases , 1998, KDD.

[147]  Ran Wolff,et al.  Privacy-preserving association rule mining in large-scale distributed systems , 2004, IEEE International Symposium on Cluster Computing and the Grid, 2004. CCGrid 2004..

[148]  Vasant Honavar,et al.  Inter-element dependency models for sequence classification , 2004 .

[149]  Jeff Heflin,et al.  Coping with Changing Ontologies in a Distributed Environment , 1999 .

[150]  Robert L. Grossman,et al.  The Preliminary Design of Papyrus: A System for High Performance Distributed Data Mining over Cluste , 1998, AAAI 1998.

[151]  Alon Y. Halevy,et al.  The Nimble XML data integration system , 2001, Proceedings 17th International Conference on Data Engineering.

[152]  J. Rissanen,et al.  Modeling By Shortest Data Description* , 1978, Autom..

[153]  Laura M. Haas,et al.  DiscoveryLink: A system for integrated access to life sciences data sources , 2001, IBM Syst. J..

[154]  Limsoon Wong,et al.  The Kleisli Query System as a Backbone for Bioinformatics Data Integration and Analysis , 2003, Bioinformatics.

[155]  Thierry Barsalou,et al.  M(DM): an open framework for interoperation of multimodel multidatabase systems , 1992, [1992] Eighth International Conference on Data Engineering.

[156]  Wenliang Du,et al.  Privacy-preserving cooperative scientific computations , 2001, Proceedings. 14th IEEE Computer Security Foundations Workshop, 2001..

[157]  Daphne Koller,et al.  Probabilistic Relational Models , 1999, ILP.

[158]  Foster J. Provost,et al.  A Survey of Methods for Scaling Up Inductive Algorithms , 1999, Data Mining and Knowledge Discovery.

[159]  Sally I. McClean,et al.  A Scalable Approach to Integrating Heterogeneous Aggregate Views of Distributed Databases , 2003, IEEE Trans. Knowl. Data Eng..

[160]  John Langford,et al.  Quantitatively tight sample complexity bounds , 2002 .

[161]  Vasant Honavar,et al.  Analysis and Synthesis of Agents That Learn from Distributed Dynamic Data Sources , 2001, Emergent Neural Computational Architectures Based on Neuroscience.

[162]  R. Stephenson A and V , 1962, The British journal of ophthalmology.

[163]  Usama M. Fayyad,et al.  On the Handling of Continuous-Valued Attributes in Decision Tree Generation , 1992, Machine Learning.

[164]  Vasant Honavar,et al.  Mobile Intelligent Agents for Document Classification and Retrieval: A Machine Learning Approach , 1998 .

[165]  Thore Graepel,et al.  From Margin to Sparsity , 2000, NIPS.

[166]  Yehuda Lindell,et al.  Privacy Preserving Data Mining , 2002, Journal of Cryptology.

[167]  Osmar R. Zaïane,et al.  Fast parallel association rule mining without candidacy generation , 2001, Proceedings 2001 IEEE International Conference on Data Mining.

[168]  David Haussler,et al.  Quantifying Inductive Bias: AI Learning Algorithms and Valiant's Learning Framework , 1988, Artif. Intell..

[169]  Raghu Ramakrishnan,et al.  Database Management Systems , 1976 .

[170]  Vasant Honavar,et al.  Identifying protein-protein interaction sites from surface residues-a support vector machine approac , 2004 .

[171]  Vasant Honavar,et al.  Ontology-Extended Component-Based Workflows : A Framework for Constructing Complex Workflows from Semantically Heterogeneous Software Components , 2004, SWDB.

[172]  Rakesh Agrawal,et al.  Privacy-preserving data mining , 2000, SIGMOD 2000.

[173]  Jing Zhang,et al.  Densityplot Matrix Display for Large Distributed Data , 2003 .

[174]  Andreas Buja,et al.  Data mining criteria for tree-based regression and classification , 2001, KDD '01.

[175]  Anthony Rowe,et al.  Discovery net: towards a grid of knowledge discovery , 2002, KDD.

[176]  Robert L. Grossman,et al.  Data mining tasks and methods: parallel methods for scaling data mining algorithms to large data sets , 2002 .

[177]  Ali R. Hurson,et al.  A taxonomy and current issues in multidatabase systems , 1992, Computer.

[178]  Rong Chen,et al.  Distributed Web mining using Bayesian networks from multiple data streams , 2001, Proceedings 2001 IEEE International Conference on Data Mining.

[179]  M. Field,et al.  Robust Order Statistics based Ensembles for Distributed Data Mining , 2000 .

[180]  SarawagiSunita,et al.  Data mining models as services on the internet , 2000 .

[181]  Ian T. Foster,et al.  The data grid: Towards an architecture for the distributed management and analysis of large scientific datasets , 2000, J. Netw. Comput. Appl..