Search results for "OLAP"

Hits ?▲	Authors	Title	Venue	Year	Link	Author keywords
44	Xiaolei Li 0001, Jiawei Han 0001, Zhijun Yin, Jae-Gil Lee 0001, Yizhou Sun	Sampling cube: a framework for statistical olap over sampling data.	SIGMOD Conference	2008	DBLP DOI BibTeX RDF	olap sampling
44	Franck Ravat, Olivier Teste, Ronan Tournier, Gilles Zurfluh	Top_Keyword: An Aggregation Function for Textual Document OLAP.	DaWaK	2008	DBLP DOI BibTeX RDF	Textual measure, Data warehouse, OLAP, Aggregation function
44	Maciej Kiewra	Representation of Uncertain Knowledge in Probabilistic OLAP Model.	KES (2)	2008	DBLP DOI BibTeX RDF	knowledge management, uncertainty, data warehouse, OLAP, probabilistic databases, multidimensional model
44	Chantola Kit, Toshiyuki Amagasa, Hiroyuki Kitagawa	Algorithms for efficient structure-based grouping in XML-OLAP.	iiWAS	2008	DBLP DOI BibTeX RDF	TOPOLOGICAL ROLLUP, XML-OLAP, XML, structural join
44	Jarernsri L. Mitrpanont, Somchart Fugkeaw	Design and development of a multiversion OLAP application.	SAC	2006	DBLP DOI BibTeX RDF	OLAP query, query rewriting technique, temporal version, multidimensional database
44	Michael Lawrence	Multiobjective genetic algorithms for materialized view selection in OLAP data warehouses.	GECCO	2006	DBLP DOI BibTeX RDF	multiobjective evolutionary optimization, genetic algorithms, OLAP, multiobjective optimization, data warehousing, view selection
44	Byeong-Seob You, Dong-Wook Lee, Sang Hun Eo, Jae-dong Lee, Hae-Young Bae	Hybrid Index for Spatio-temporal OLAP Operations.	ADVIS	2006	DBLP DOI BibTeX RDF	Aggregation R-tree, OLAP, Spatio-Temporal, Spatial Data Warehouse
44	Mehmet Kaya, Reda Alhajj	Extending OLAP with Fuzziness for Effective Mining of Fuzzy Multidimensional Weighted Association Rules.	ADMA	2006	DBLP DOI BibTeX RDF	fuzzy data cube, multidimensional mining, weighted mining, data mining, association rules, OLAP
44	Riadh Ben Messaoud, Sabine Loudcher Rabaséda, Omar Boussaid, Rokia Missaoui	Enhanced mining of association rules from data cubes.	DOLAP	2006	DBLP DOI BibTeX RDF	association rules, OLAP, data cubes
44	Igor Timko, Curtis E. Dyreson, Torben Bach Pedersen	Pre-aggregation with probability distributions.	DOLAP	2006	DBLP DOI BibTeX RDF	pre-aggregation, location-based services, OLAP, data warehousing, probability distributions, approximate query processing, aggregation queries, incomplete data
44	Alfredo Cuzzocrea	Overcoming Limitations of Approximate Query Answering in OLAP.	IDEAS	2005	DBLP DOI BibTeX RDF	Approximatee Query Answering, Dimensionality Reduction, OLAP, Probabilistic Guarantees
44	Matthew Scotch, Bambang Parmanto	SOVAT: Spatial OLAP Visualization and Analysis Tool.	HICSS	2005	DBLP DOI BibTeX RDF	community health assessment, GIS, OLAP
44	Juan Manuel Pérez, Rafael Berlanga Llavori, María José Aramburu, Torben Bach Pedersen	A relevance-extended multi-dimensional model for a data warehouse contextualized with documents.	DOLAP	2005	DBLP DOI BibTeX RDF	text-rich XML documents, OLAP
44	Ricky W. K. Leung, Henry C. W. Lau, C. K. Kwong 0001	An Intelligent System to Monitor the Chemical Concentration of Electroplating Process: An Integrated OLAP and Fuzzy Logic Approach.	Artif. Intell. Rev.	2004	DBLP DOI BibTeX RDF	knowledge learning, machine learning, fuzzy logic, On-Line Analytical Processing (OLAP)
44	Mehmet Kaya, Reda Alhajj	Utilizing Fuzzy OLAP Mining Towards Novel Approach to Multiagent Modular Reinforcement Learning.	IAT	2004	DBLP DOI BibTeX RDF	data mining, reinforcement learning, multiagent systems, OLAP, fuzziness, data cube
44	Emiel Caron, Hennie Daniels	Automated business diagnosis in the OLAP context.	OR	2004	DBLP DOI BibTeX RDF	OLAP, Explanation, Business Intelligence, Datamining
44	Mark Sifer	A visual interface technique for exploring OLAP data with coordinated dimension hierarchies.	CIKM	2003	DBLP DOI BibTeX RDF	interface, OLAP, hierarchies, data exploration
44	Yannis Sismanis, Antonios Deligiannakis, Yannis Kotidis, Nick Roussopoulos	Hierarchical dwarfs for the rollup cube.	DOLAP	2003	DBLP DOI BibTeX RDF	dwarf cube, prefix elimination, structural redundancy, suffix coalescing, indexing, aggregation, OLAP, granularity, data cubes, materialization, warehouses
44	Seigo Muto, Masaru Kitsuregawa	A Dynamic Load Balancing Strategy for Parallel Datacube Computation.	DOLAP	1999	DBLP DOI BibTeX RDF	parallel processing, OLAP, dynamic load balancing, datacube
44	Véronique Cariou, Jérôme Cubillé, Christian Derquenne, Sabine Goutier, Françoise Guisnel, Henri Klajnmic	Built-In Indicators to Discover Interesting Drill Paths in a Cube.	DaWaK	2008	DBLP DOI BibTeX RDF	Olap Mining, Oracle 10g, Data Mining, OLAP, Data cube
44	Véronique Cariou, Jérôme Cubillé, Christian Derquenne, Sabine Goutier, Françoise Guisnel, Henri Klajnmic	Built-In Indicators to Automatically Detect Interesting Cells in a Cube.	DaWaK	2007	DBLP DOI BibTeX RDF	Olap Mining, Atypical Values, Test-value, Oracle 10g, Data Mining, OLAP, Data cube, Chi-Square
43	Yannis Sismanis, Ling Wang, Ariel Fuxman, Peter J. Haas, Berthold Reinwald	Resolution-Aware Query Answering for Business Intelligence.	ICDE	2009	DBLP DOI BibTeX RDF
43	Houssem Jerbi, Franck Ravat, Olivier Teste, Gilles Zurfluh	Management of context-aware preferences in multidimensional databases.	ICDIM	2008	DBLP DOI BibTeX RDF
43	Todd Eavis, George Dimitrov, Ivan Dimitrov, David Cueva, Alex Lopez, Ahmad Taleb	Sidera: A Cluster-Based Server for Online Analytical Processing.	OTM Conferences (2)	2007	DBLP DOI BibTeX RDF
43	Huei-Huang Chen, Kuo-Wei Ho	Implementing Data Cubes via Subcubes.	IDEAS	2004	DBLP DOI BibTeX RDF
43	Jane Zhao, Hui Ma 0001	Quality-Assured Design of On-Line Analytical Processing Systems using Abstract State Machines.	QSIC	2004	DBLP DOI BibTeX RDF	Quality Design, Data Warehouse, Abstract State Machine, On-Line Analytical Processing
43	Jian Pei	A General Model for Online Analytical Processing of Complex Data.	ER	2003	DBLP DOI BibTeX RDF
43	Jeffrey Scott Vitter, Min Wang 0001	Approximate Computation of Multidimensional Aggregates of Sparse Data Using Wavelets.	SIGMOD Conference	1999	DBLP DOI BibTeX RDF
41	Kamel Aouiche, Daniel Lemire	A comparison of five probabilistic view-size estimation techniques in OLAP.	DOLAP	2007	DBLP DOI BibTeX RDF	random hashing, view-size estimation, data warehouse, OLAP, materialized views
41	John Horner, Il-Yeol Song, Peter P. Chen	An analysis of additivity in OLAP systems.	DOLAP	2004	DBLP DOI BibTeX RDF	metadata, data warehouse, OLAP, summarization, additivity
41	Mathurin Body, Maryvonne Miquel, Yvan Bédard, Anne Tchounikine	A multidimensional and multiversion structure for OLAP applications.	DOLAP	2002	DBLP DOI BibTeX RDF	conceptual model, data warehouse, OLAP, temporal evolution
41	Karl Hahn, Carsten Sapia, Markus Blaschka	Automatically Generating OLAP Schemata from Conceptual Graphical Models.	DOLAP	2000	DBLP DOI BibTeX RDF	graphical multidimensional modeling notation, multidimensional schema generation, data warehouse, OLAP, conceptual design
41	Torsten Priebe, Günther Pernul	Towards OLAP Security Design - Survey and Research Issues.	DOLAP	2000	DBLP DOI BibTeX RDF	security, design, access control, data warehouse, OLAP
41	Barbara Dinter, Carsten Sapia, Gabriele Höfling, Markus Blaschka	The OLAP Market: State of the Art and Research Issues.	DOLAP	1998	DBLP DOI BibTeX RDF	MOLAP, ROLAP, market survey, data warehouse, OLAP, state of the art, research issues
40	Benjamin Leonhardi, Bernhard Mitschang, Rubén Pulido de los Reyes, Christoph Sieb, Michael Wurst	Augmenting OLAP exploration with dynamic advanced analytics.	EDBT	2010	DBLP DOI BibTeX RDF
40	Bernhard Jaecksch, Wolfgang Lehner, Franz Faerber	A plan for OLAP.	EDBT	2010	DBLP DOI BibTeX RDF
40	Weiji Xiao, Jianqing Xi	CCBitmaps: A Space-Time Efficient Index Structure for OLAP.	ADMA	2009	DBLP DOI BibTeX RDF	Quotient Cube, Closed Cube, QC-Trees, CC-Bitmaps, CCListsIntersection
40	Jiawei Han 0001, Xifeng Yan, Philip S. Yu	Scalable OLAP and mining of information networks.	EDBT	2009	DBLP DOI BibTeX RDF
40	Alfredo Cuzzocrea	Multiple-Objective Compression of Data Cubes in Cooperative OLAP Environments.	ADBIS	2008	DBLP DOI BibTeX RDF
40	Ronnie Alves, Orlando Belo, Fabio Costa	Effective OLAP Mining of Evolving Data Marts.	IDEAS	2007	DBLP DOI BibTeX RDF
40	Svetlana Mansmann, Thomas Neumuth, Marc H. Scholl	OLAP Technology for Business Process Intelligence: Challenges and Solutions.	DaWaK	2007	DBLP DOI BibTeX RDF
40	Jorge Loureiro, Orlando Belo	A Metamorphosis Algorithm for the Optimization of a Multi-node OLAP System.	EPIA Workshops	2007	DBLP DOI BibTeX RDF
40	Svetlana Vinnik, Florian Mansmann	From Analysis to Interactive Exploration: Building Visual Hierarchies from OLAP Cubes.	EDBT	2006	DBLP DOI BibTeX RDF
40	Mehmet Kaya, Reda Alhajj	Fuzzy OLAP association rules mining-based modular reinforcement learning approach for multiagent systems.	IEEE Trans. Syst. Man Cybern. Part B	2005	DBLP DOI BibTeX RDF
40	John Horner, Il-Yeol Song	A Taxonomy of Inaccurate Summaries and Their Management in OLAP Systems.	ER	2005	DBLP DOI BibTeX RDF
40	Lin Yuan, Hengming Zou, Zhanhuai Li	A Solution to Ragged Dimension Problem in OLAP.	ICNC (3)	2005	DBLP DOI BibTeX RDF
40	Camille Furtado, Alexandre A. B. Lima, Esther Pacitti, Patrick Valduriez, Marta Mattoso	Physical and Virtual Partitioning in OLAP Database Clusters.	SBAC-PAD	2005	DBLP DOI BibTeX RDF
40	Elzbieta Malinowski, Esteban Zimányi	OLAP Hierarchies: A Conceptual Perspective.	CAiSE	2004	DBLP DOI BibTeX RDF
40	Lingyu Wang 0001, Sushil Jajodia, Duminda Wijesekera	Securing OLAP Data Cubes Against Privacy Breaches.	S&P	2004	DBLP DOI BibTeX RDF
40	Carlos A. Hurtado, Claudio Gutierrez 0001	Equivalence of OLAP Dimension Schemas.	FoIKS	2004	DBLP DOI BibTeX RDF
40	Elaheh Pourabbas, Arie Shoshani	Answering Joint Queries from Multiple Aggregate OLAP Databases.	DaWaK	2003	DBLP DOI BibTeX RDF
40	Fuat Akal, Klemens Böhm, Hans-Jörg Schek	OLAP Query Evaluation in a Database Cluster: A Performance Study on Intra-Query Parallelism.	ADBIS	2002	DBLP DOI BibTeX RDF
40	Torsten Priebe, Günther Pernul	A Pragmatic Approach to Conceptual Modeling of OLAP Security.	ER	2001	DBLP DOI BibTeX RDF
40	Nikos Karayannidis, Aris Tsois, Panos Vassiliadis, Timos K. Sellis	Design of the ERATOSTHENES OLAP Server.	Panhellenic Conference on Informatics	2001	DBLP DOI BibTeX RDF
40	Qiming Chen, Meichun Hsu, Umeshwar Dayal	A Data-Warehouse/OLAP Framework for Scalable Telecommunication Tandem Traffic Analysis.	ICDE	2000	DBLP DOI BibTeX RDF
40	Andrey Balmin, Yannis Papakonstantinou, Thanos Papadimitriou	Optimization of Hypothetical Queries in an OLAP Environment.	ICDE	2000	DBLP DOI BibTeX RDF
40	Qiming Chen, Umeshwar Dayal, Meichun Hsu	An OLAP-based Scalable Web Access Analysis Engine.	DaWaK	2000	DBLP DOI BibTeX RDF
40	Qiming Chen, Umeshwar Dayal, Meichun Hsu	OLAP-based Scalable Profiling of Customer Behavior.	DaWaK	1999	DBLP DOI BibTeX RDF
40	Shin-Chung Shao	Multivariate and Multidimensional OLAP.	EDBT	1998	DBLP DOI BibTeX RDF
40	Surajit Chaudhuri, Umeshwar Dayal	An Overview of Data Warehousing and OLAP Technology.	SIGMOD Rec.	1997	DBLP DOI BibTeX RDF
39	Chun Kit Chui, Eric Lo 0001, Ben Kao, Wai-Shing Ho	Supporting ranking pattern-based aggregate queries in sequence data cubes.	CIKM	2009	DBLP DOI BibTeX RDF	query processing, OLAP, sequence, data cube, top-k
39	Alejandro A. Vaisman, Esteban Zimányi	A multidimensional model representing continuous fields in spatial data warehouses.	GIS	2009	DBLP DOI BibTeX RDF	GIS, query languages, OLAP
39	Ping Wu, Yannis Sismanis, Berthold Reinwald	Towards keyword-driven analytical processing.	SIGMOD Conference	2007	DBLP DOI BibTeX RDF	ranking, data warehouse, aggregation, OLAP, keyword search
39	Frank K. H. A. Dehne, Todd Eavis, Andrew Rau-Chaplin	Parallel Multi-Dimensional ROLAP Indexing.	CCGRID	2003	DBLP DOI BibTeX RDF	Management of large scale distributed data, Parallel ROLAP Indexing, Cluster and Grid Applications, OLAP, Datacube
39	Torben Bach Pedersen, Christian S. Jensen, Curtis E. Dyreson	Supporting Imprecision in Multidimensional Databases Using Granularities.	SSDBM	1999	DBLP DOI BibTeX RDF	Data Imprecision, OLAP, Granularities, Multidimensional databases
36	Carlos A. Hurtado, Alberto O. Mendelzon, Alejandro A. Vaisman	Updating OLAP Dimensions.	DOLAP	1999	DBLP DOI BibTeX RDF
36	Elaheh Pourabbas, Maurizio Rafanelli	Characterization of Hierarchies and Some Operators in OLAP Environment.	DOLAP	1999	DBLP DOI BibTeX RDF
36	Ho Jin Woo, Se Jung Shin, Woo Sock Yang, Won Suk Lee	DS-Cuber: an integrated OLAP environment for data streams.	CIKM	2009	DBLP DOI BibTeX RDF	data streams, OLAP, data cube
36	Bin Zhou 0002, Daxin Jiang, Jian Pei, Hang Li	OLAP on search logs: an infrastructure supporting data-driven applications in search engines.	KDD	2009	DBLP DOI BibTeX RDF	query session, OLAP, suffix tree, search log
36	Octavio Glorio, Juan Trujillo 0001	Designing Data Warehouses for Geographic OLAP Querying by Using MDA.	ICCSA (1)	2009	DBLP DOI BibTeX RDF	Spatial data warehousing, GIS-OLAP, MDA
36	Houssem Jerbi, Franck Ravat, Olivier Teste, Gilles Zurfluh	Applying Recommendation Technology in OLAP Systems.	ICEIS	2009	DBLP DOI BibTeX RDF	Decision-support analysis, OLAP, Recommendations, Preferences
36	Sergio Di Martino, Sandro Bimonte, Michela Bertolotto, Filomena Ferrucci	Integrating Google Earth within OLAP Tools for Multidimensional Exploration and Analysis of Spatial Data.	ICEIS	2009	DBLP DOI BibTeX RDF	Spatial Decision Support Systems, Data Visualization, Spatial Data Warehouses, Spatial OLAP
36	Torben Bach Pedersen, Il-Yeol Song	Report on the Tenth ACM International Workshop on Data Warehousing and OLAP (DOLAP'07).	SIGMOD Rec.	2008	DBLP DOI BibTeX RDF	data warehousing, on-line analytical processing (OLAP)
36	Cyrus Shahabi, Mehrdad Jahangiri, Farnoush Banaei Kashani	ProDA: An End-to-End Wavelet-Based OLAP System for Massive Datasets.	Computer	2008	DBLP DOI BibTeX RDF	online query processing, range aggregate queries, OLAP tools, wavelet transformation, database management, scientific applications, data-intensive computing, information technology and systems
36	Nikos Karayannidis, Timos K. Sellis	Hierarchical clustering for OLAP: the CUBE File approach.	VLDB J.	2008	DBLP DOI BibTeX RDF	CUBE File, Physical data clustering, OLAP, Hierarchical clustering, Data cube
36	Alfredo Cuzzocrea, Domenico Saccà	H-IQTS: a semantics-aware histogram for compressing categorical OLAP data.	IDEAS	2008	DBLP DOI BibTeX RDF	data cube compression, semantics, OLAP, histograms
36	Carlos Blanco 0001, Eduardo Fernández-Medina, Juan Trujillo 0001, Mario Piattini	Implementing Multidimensional Security into OLAP Tools.	ARES	2008	DBLP DOI BibTeX RDF	SQL Server Analysis Services 2008, security, MDA, Data Warehouses, OLAP, multidimensional modeling
36	Jesús Pardillo, Jose-Norberto Mazón, Juan Trujillo 0001	Model-Driven Metadata for OLAP Cubes from the Conceptual Modelling of Data Warehouses.	DaWaK	2008	DBLP DOI BibTeX RDF	conceptual modelling, data warehouse, OLAP, model-driven engineering, multidimensional modelling, customisation
36	Leticia I. Gómez, Alejandro A. Vaisman, Sebastián Zich	Piet-QL: a query language for GIS-OLAP integration.	GIS	2008	DBLP DOI BibTeX RDF	GIS, query languages, OLAP
36	Kamel Aouiche, Daniel Lemire, Robert Godin	Web 2.0 OLAP: From Data Cubes to Tag Clouds.	WEBIST (Selected Papers)	2008	DBLP DOI BibTeX RDF	Data warehouse, OLAP, Business intelligence, Social web, Tag cloud
36	Rokia Missaoui, Cyril Goutte, Anicet Kouomou Choupo, Ameur Boujenoui	A probabilistic model for data cube compression and query approximation.	DOLAP	2007	DBLP DOI BibTeX RDF	non-negative multi-way array factorization, data mining, approximation, compression, OLAP, data warehousing, data cubes, log-linear modeling
36	Bing Liu 0001, Kaidi Zhao, Jeffrey Benkler, Weimin Xiao	Rule interestingness analysis using OLAP operations.	KDD	2006	DBLP DOI BibTeX RDF	diagnostic data mining, general impressions, interestingness analysis, OLAP, class association rules
36	Hongzhi Wang 0001, Jianzhong Li 0001, Zhenying He, Hong Gao 0001	OLAP for XML Data.	CIT	2005	DBLP DOI BibTeX RDF	GXaggregation, XCube, XML, OLAP
36	Frank K. H. A. Dehne, Todd Eavis, Andrew Rau-Chaplin	Parallel querying of ROLAP cubes in the presence of hierarchies.	DOLAP	2005	DBLP DOI BibTeX RDF	parallelization, caching, indexing, aggregation, OLAP, hierarchies, granularity, data cubes, materialization
36	Wen-Yang Lin, I-Chung Kuo	A Genetic Selection Algorithm for OLAP Data Cubes.	Knowl. Inf. Syst.	2004	DBLP DOI BibTeX RDF	Genetic algorithms, Data warehouse, OLAP, Data cubes, Multidimensional database, Greedy method
36	John R. Smith, Chung-Sheng Li, Anant Jhingran	A Wavelet Framework for Adapting Data Cube Views for OLAP.	IEEE Trans. Knowl. Data Eng.	2004	DBLP DOI BibTeX RDF	multidimensional data management, Databases, wavelets, decision support, OLAP, data cubes, data organization
36	Thomas P. Nadeau, Toby J. Teorey	A Pareto Model for OLAP View Size Estimation.	Inf. Syst. Frontiers	2003	DBLP DOI BibTeX RDF	view size estimation, materialized view selection, OLAP, Pareto distribution
36	Alberto Abelló, José Samos, Fèlix Saltor	Implementing operations to navigate semantic star schemas.	DOLAP	2003	DBLP DOI BibTeX RDF	OLAP operations, drill-across, SQL, semantic relationships, star schema
36	Robert M. Bruckner, Tok Wang Ling, Oscar Mangisengi, A Min Tjoa	A Framework for a Multidimensional OLAP Model using Topic Maps.	WISE (2)	2001	DBLP DOI BibTeX RDF	Ontologies, XML, Interoperability, Data Warehouse, OLAP, Topic Maps
36	Volker Markl, Frank Ramsak, Rudolf Bayer	Improving OLAP Performance by Multidimensional Hierarchical Clustering.	IDEAS	1999	DBLP DOI BibTeX RDF	relational OLAP, aggregation, hierarchies, hierarchical clustering, data warehousing, UB-Tree, multidimensional access methods
36	Xiaofang Zhou 0001, David Truffet, Jiawei Han 0001	Efficient Polygon Amalgamation Methods for Spatial OLAP and Spatial Data Mining.	SSD	1999	DBLP DOI BibTeX RDF	polygon amalgamation, spatial databases, spatial indexing, on-line analytical processing (OLAP)
34	Alfredo Cuzzocrea	CAMS: OLAPing Multidimensional Data Streams Efficiently.	DaWaK	2009	DBLP DOI BibTeX RDF
34	Zhixian Niu, Lili Zong, Qingwei Yan, Zhenxing Zhao	Auto-recognizing DBMS Workload Based on C5.0 Algorithm.	WKDD	2009	DBLP DOI BibTeX RDF
34	Cindy Xide Lin, Bolin Ding, Jiawei Han 0001, Feida Zhu 0001, Bo Zhao 0001	Text Cube: Computing IR Measures for Multidimensional Text Database Analysis.	ICDM	2008	DBLP DOI BibTeX RDF
34	Frank K. H. A. Dehne, Michael Lawrence	Cooperative Caching for Grid Based DataWarehouses.	CCGRID	2007	DBLP DOI BibTeX RDF
34	Dehui Zhang, Shaohua Tan, Dongqing Yang, Shiwei Tang, Xiuli Ma, Lizheng Jiang	Dynamic Construction of User Defined Virtual Cubes.	NGITS	2006	DBLP DOI BibTeX RDF
34	Songting Chen, Elke A. Rundensteiner	GPIVOT: Efficient Incremental Maintenance of Complex ROLAP Views.	ICDE	2005	DBLP DOI BibTeX RDF
34	Yu Li, Aijun An	Representing UML Snowflake Diagram from Integrating XML Data Using XML Schema.	DEEC	2005	DBLP DOI BibTeX RDF
34	Jane Zhao	A Formal Approach to the Design of Distributed Data Warehouses.	ICCSA (2)	2005	DBLP DOI BibTeX RDF
34	Dennis Pedersen, Torben Bach Pedersen, Karsten Riis	The Decoration Operator: A Foundation for On-Line Dimensional Data Integration.	IDEAS	2004	DBLP DOI BibTeX RDF