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*Data Mining: Concepts and Techniques*Data Mining: Concepts and Techniques Chapter 2 Jiawei HanDepartment of Computer Science University of Illinois at Urbana-Champaignwww.cs.uiuc.edu/~hanj2006 Jiawei Han and Micheline Kamber, All rights reserved

Data Mining: Concepts and Techniques

*Data Mining: Concepts and Techniques*


*Data Mining: Concepts and Techniques*Chapter 2: Data PreprocessingWhy preprocess the data?Descriptive data summarizationData cleaning Data integration and transformationData reductionDiscretization and concept hierarchy generationSummary


*Data Mining: Concepts and Techniques*Why Data Preprocessing?Data in the real world is dirtyincomplete: lacking attribute values, lacking certain attributes of interest, or containing only aggregate datae.g., occupation= noisy: containing errors or outlierse.g., Salary=-10inconsistent: containing discrepancies in codes or namese.g., Age=42 Birthday=03/07/1997e.g., Was rating 1,2,3, now rating A, B, Ce.g., discrepancy between duplicate records


*Data Mining: Concepts and Techniques*Why Is Data Dirty?Incomplete data may come fromNot applicable data value when collectedDifferent considerations between the time when the data was collected and when it is analyzed.Human/hardware/software problemsNoisy data (incorrect values) may come fromFaulty data collection instrumentsHuman or computer error at data entryErrors in data transmissionInconsistent data may come fromDifferent data sourcesFunctional dependency violation (e.g., modify some linked data)Duplicate records also need data cleaning


*Data Mining: Concepts and Techniques*Why Is Data Preprocessing Important?No quality data, no quality mining results!Quality decisions must be based on quality datae.g., duplicate or missing data may cause incorrect or even misleading statistics.Data warehouse needs consistent integration of quality dataData extraction, cleaning, and transformation comprises the majority of the work of building a data warehouse


*Data Mining: Concepts and Techniques*Multi-Dimensional Measure of Data QualityA well-accepted multidimensional view:AccuracyCompletenessConsistencyTimelinessBelievabilityValue addedInterpretabilityAccessibilityBroad categories:Intrinsic, contextual, representational, and accessibility

Data Mining: Concepts and Techniques*

*Data Mining: Concepts and Techniques*Major Tasks in Data PreprocessingData cleaningFill in missing values, smooth noisy data, identify or remove outliers, and resolve inconsistenciesData integrationIntegration of multiple databases, data cubes, or filesData transformationNormalization and aggregationData reductionObtains reduced representation in volume but produces the same or similar analytical resultsData discretizationPart of data reduction but with particular importance, especially for numerical data


*Data Mining: Concepts and Techniques*Forms of Data Preprocessing


*Data Mining: Concepts and Techniques*Mining Data Descriptive CharacteristicsMotivationTo better understand the data: central tendency, variation and spreadData dispersion characteristics median, max, min, quantiles, outliers, variance, etc.Numerical dimensions correspond to sorted intervalsData dispersion: analyzed with multiple granularities of precisionBoxplot or quantile analysis on sorted intervalsDispersion analysis on computed measuresFolding measures into numerical dimensionsBoxplot or quantile analysis on the transformed cube


*Data Mining: Concepts and Techniques*Measuring the Central TendencyMean (algebraic measure) (sample vs. population):Weighted arithmetic mean:Trimmed mean: chopping extreme valuesMedian: A holistic measureMiddle value if odd number of values, or average of the middle two values otherwiseEstimated by interpolation (for grouped data):ModeValue that occurs most frequently in the dataUnimodal, bimodal, trimodalEmpirical formula:


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*Data Mining: Concepts and Techniques* Symmetric vs. Skewed DataMedian, mean and mode of symmetric, positively and negatively skewed data


*Data Mining: Concepts and Techniques*Measuring the Dispersion of DataQuartiles, outliers and boxplotsQuartiles: Q1 (25th percentile), Q3 (75th percentile)Inter-quartile range: IQR = Q3 Q1 Five number summary: min, Q1, M, Q3, maxBoxplot: ends of the box are the quartiles, median is marked, whiskers, and plot outlier individuallyOutlier: usually, a value higher/lower than 1.5 x IQRVariance and standard deviation (sample: s, population: )Variance: (algebraic, scalable computation)

Standard deviation s (or ) is the square root of variance s2 (or 2)


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*Data Mining: Concepts and Techniques*Properties of Normal Distribution CurveThe normal (distribution) curveFrom to +: contains about 68% of the measurements (: mean, : standard deviation) From 2 to +2: contains about 95% of itFrom 3 to +3: contains about 99.7% of it


*Data Mining: Concepts and Techniques* Boxplot AnalysisFive-number summary of a distribution:

Minimum, Q1, M, Q3, MaximumBoxplotData is represented with a boxThe ends of the box are at the first and third quartiles, i.e., the height of the box is IRQThe median is marked by a line within the boxWhiskers: two lines outside the box extend to Minimum and Maximum


*Data Mining: Concepts and Techniques*Visualization of Data Dispersion: Boxplot Analysis


*Data Mining: Concepts and Techniques*Histogram AnalysisGraph displays of basic statistical class descriptionsFrequency histograms A univariate graphical methodConsists of a set of rectangles that reflect the counts or frequencies of the classes present in the given data


*Data Mining: Concepts and Techniques*Quantile PlotDisplays all of the data (allowing the user to assess both the overall behavior and unusual occurrences)Plots quantile informationFor a data xi data sorted in increasing order, fi indicates that approximately 100 fi% of the data are below or equal to the value xi


*Data Mining: Concepts and Techniques*Quantile-Quantile (Q-Q) PlotGraphs the quantiles of one univariate distribution against the corresponding quantiles of anotherAllows the user to view whether there is a shift in going from one distribution to another


*Data Mining: Concepts and Techniques*Scatter plotProvides a first look at bivariate data to see clusters of points, outliers, etcEach pair of values is treated as a pair of coordinates and plotted as points in the plane


*Data Mining: Concepts and Techniques*Loess CurveAdds a smooth curve to a scatter plot in order to provide better perception of the pattern of dependenceLoess curve is fitted by setting two parameters: a smoothing parameter, and the degree of the polynomials that are fitted by the regression


*Data Mining: Concepts and Techniques*Positively and Negatively Correlated Data


*Data Mining: Concepts and Techniques* Not Correlated Data


*Data Mining: Concepts and Techniques*Graphic Displays of Basic Statistical DescriptionsHistogram: (shown before)Boxplot: (covered before)Quantile plot: each value xi is paired with fi indicating that approximately 100 fi % of data are xi Quantile-quantile (q-q) plot: graphs the quantiles of one univariant distribution against the corresponding quantiles of anotherScatter plot: each pair of values is a pair of coordinates and plotted as points in the planeLoess (local regression) curve: add a smooth curve to a scatter plot to provide better perception of the pattern of dependence


*Data Mining: Concepts and Techniques*Data CleaningImportanceData cleaning is one of the three biggest problems in data warehousingRalph KimballData cleaning is the number one problem in data warehousingDCI surveyData cleaning tasksFill in missing valuesIdentify outliers and smooth out noisy data Correct inconsistent dataResolve redundancy caused by data integration


*Data Mining: Concepts and Techniques*Missing DataData is not always availableE.g., many tuples have no recorded value for several attributes, such as customer income in sales dataMissing data may be due to equipment malfunctioninconsistent with other recorded data and thus deleteddata not entered due to misunderstandingcertain data may not be considered important at the time of entrynot register history or changes of the dataMissing data may need to be inferred.


*Data Mining: Concepts and Techniques*How to Handle Missing Data?Ignore the tuple: usually done when class label is missing (assuming the tasks in classificationnot effective when the percentage of missing values per attribute varies considerably.Fill in the missing value manually: tedious + infeasible?Fill in it automatically witha global constant : e.g., unknown, a new class?! the attribute meanthe attribute mean for all samples belonging to the same class: smarterthe most probable value: inference-based such as Bayesian formula or decision tree


*Data Mining: Concepts and Techniques*Noisy DataNoise: random error or variance in a measured variableIncorrect attribute values may due tofaulty data collection instrumentsdata entry problemsdata transmission problemstechnology limitationinconsistency in naming convention Other data problems which requires data cleaningduplicate recordsincomplete datainconsistent data


*Data Mining: Concepts and Techniques*How to Handle Noisy Data?Binningfirst sort data and partition into (equal-frequency) binsthen one can smooth by bin means, smooth by bin median, smooth by bin boundaries, etc.Regressionsmooth by fitting the data into regression functionsClusteringdetect and remove outliersCombined computer and human inspectiondetect suspicious values and check by human (e.g., deal with possible outliers)


*Data Mining: Concepts and Techniques*Simple Discretization Methods: BinningEqual-width (distance) partitioningDivides the range into N intervals of equal size: uniform gridif A and B are the lowest and highest values of the attribute, the width of intervals will be: W = (B A)/N.The most straightforward, but outliers may dominate presentationSkewed data is not handled wellEqual-depth (frequency) partitioningDivides the range into N intervals, each containing approximately same number of samplesGood data scalingManaging categorical attributes can be tricky


*Data Mining: Concepts and Techniques*Binning Methods for Data SmoothingSorted data for price (in dollars): 4, 8, 9, 15, 21, 21, 24, 25, 26, 28, 29, 34* Partition into equal-frequency (equi-depth) bins: - Bin 1: 4, 8, 9, 15 - Bin 2: 21, 21, 24, 25 - Bin 3: 26, 28, 29, 34* Smoothing by bin means: - Bin 1: 9, 9, 9, 9 - Bin 2: 23, 23, 23, 23 - Bin 3: 29, 29, 29, 29* Smoothing by bin boundaries: - Bin 1: 4, 4, 4, 15 - Bin 2: 21, 21, 25, 25 - Bin 3: 26, 26, 26, 34


*Data Mining: Concepts and Techniques*Regression

xyy = x + 1X1Y1Y1


*Data Mining: Concepts and Techniques*Cluster Analysis


*Data Mining: Concepts and Techniques*Data Cleaning as a ProcessData discrepancy detectionUse metadata (e.g., domain, range, dependency, distribution)Check field overloading Check uniqueness rule, consecutive rule and null ruleUse commercial toolsData scrubbing: use simple domain knowledge (e.g., postal code, spell-check) to detect errors and make correctionsData auditing: by analyzing data to discover rules and relationship to detect violators (e.g., correlation and clustering to find outliers)Data migration and integrationData migration tools: allow transformations to be specifiedETL (Extraction/Transformation/Loading) tools: allow users to specify transformations through a graphical user interfaceIntegration of the two processesIterative and interactive (e.g., Potters Wheels)


*Data Mining: Concepts and Techniques*Chapter 2: Data PreprocessingWhy preprocess the data?Data cleaning Data integration and transformationData reductionDiscretization and concept hierarchy generationSummary


*Data Mining: Concepts and Techniques*Data IntegrationData integration: Combines data from multiple sources into a coherent storeSchema integration: e.g., A.cust-id B.cust-#Integrate metadata from different sourcesEntity identification problem: Identify real world entities from multiple data sources, e.g., Bill Clinton = William ClintonDetecting and resolving data value conflictsFor the same real world entity, attribute values from different sources are differentPossible reasons: different representations, different scales, e.g., metric vs. British units


*Data Mining: Concepts and Techniques*Handling Redundancy in Data IntegrationRedundant data occur often when integration of multiple databasesObject identification: The same attribute or object may have different names in different databasesDerivable data: One attribute may be a derived attribute in another table, e.g., annual revenueRedundant attributes may be able to be detected by correlation analysisCareful integration of the data from multiple sources may help reduce/avoid redundancies and inconsistencies and improve mining speed and quality


*Data Mining: Concepts and Techniques*Correlation Analysis (Numerical Data)Correlation coefficient (also called Pearsons product moment coefficient)

where n is the number of tuples, and are the respective means of A and B, A and B are the respective standard deviation of A and B, and (AB) is the sum of the AB cross-product.If rA,B > 0, A and B are positively correlated (As values increase as Bs). The higher, the stronger correlation.rA,B = 0: independent; rA,B < 0: negatively correlated


*Data Mining: Concepts and Techniques*Correlation Analysis (Categorical Data)2 (chi-square) test

The larger the 2 value, the more likely the variables are relatedThe cells that contribute the most to the 2 value are those whose actual count is very different from the expected countCorrelation does not imply causality# of hospitals and # of car-theft in a city are correlatedBoth are causally linked to the third variable: population


*Data Mining: Concepts and Techniques*Chi-Square Calculation: An Example

2 (chi-square) calculation (numbers in parenthesis are expected counts calculated based on the data distribution in the two categories)

It shows that like_science_fiction and play_chess are correlated in the group

Play chessNot play chessSum (row)Like science fiction250(90)200(360)450Not like science fiction50(210)1000(840)1050Sum(col.)30012001500


*Data Mining: Concepts and Techniques*Data TransformationSmoothing: remove noise from dataAggregation: summarization, data cube constructionGeneralization: concept hierarchy climbingNormalization: scaled to fall within a small, specified rangemin-max normalizationz-score normalizationnormalization by decimal scalingAttribute/feature constructionNew attributes constructed from the given ones


*Data Mining: Concepts and Techniques*Data Transformation: NormalizationMin-max normalization: to [new_minA, new_maxA]

Ex. Let income range $12,000 to $98,000 normalized to [0.0, 1.0]. Then $73,000 is mapped to Z-score normalization (: mean, : standard deviation):

Ex. Let = 54,000, = 16,000. ThenNormalization by decimal scaling

Where j is the smallest integer such that Max(||) < 1


*Data Mining: Concepts and Techniques*Data Reduction StrategiesWhy data reduction?A database/data warehouse may store terabytes of dataComplex data analysis/mining may take a very long time to run on the complete data setData reduction Obtain a reduced representation of the data set that is much smaller in volume but yet produce the same (or almost the same) analytical resultsData reduction TechniquesData cube aggregation:Dimensionality reduction e.g., remove unimportant attributesData CompressionNumerosity reduction e.g., fit data into modelsDiscretization and concept hierarchy generation


*Data Mining: Concepts and Techniques*Data Cube AggregationAggregation operations are applied to the data in construction of a data cube.Data cubes store multidimensional aggregated information.The lowest level of a data cube (base cuboid)The aggregated data for an individual entity of interestE.g., a customer in a phone calling data warehouseMultiple levels of aggregation in data cubesFurther reduce the size of data to deal with


Reference appropriate levelsUse the smallest representation which is enough to solve the taskQueries regarding aggregated information should be answered using data cube, when possible



*DW/DM: Data cube Computation*A Data Cube

Cor1Cor2Cam1Cam2Lex1Lex2DammamJeddahRiyadhAllAllBranchProductAggregate cellBase cellApex CuboidProduct cuboidBranch cuboidBase cuboid

101112310111969671298573

474844

332926172311

139

DW/DM: Data cube Computation

*Data Mining: Concepts and Techniques*Attribute Subset Selectionattribute subset selection:Select a minimum set of features such that the probability distribution of different classes given the values for those features is as close as possible to the original distribution given the values of all featuresreduce # of patterns in the patterns, easier to understandHeuristic methods (due to exponential # of choices):Step-wise forward selectionStep-wise backward eliminationCombining forward selection and backward eliminationDecision-tree induction


*Data Mining: Concepts and Techniques*Example of Decision Tree InductionInitial attribute set:{A1, A2, A3, A4, A5, A6}

A4 ?

A1?A6?

Class 1Class 2Class 1Class 2

Reduced attribute set: {A1, A4, A6}


*Data Mining: Concepts and Techniques*Heuristic Feature Selection MethodsThere are 2d possible sub-features of d featuresSeveral heuristic feature selection methods:Best single features under the feature independence assumption: choose by significance testsBest step-wise feature selection: The best single-feature is picked firstThen next best feature condition to the first, ...Step-wise feature elimination:Repeatedly eliminate the worst featureBest combined feature selection and eliminationOptimal branch and bound:Use feature elimination and backtracking


*Data Mining: Concepts and Techniques*Data CompressionString compressionThere are extensive theories and well-tuned algorithmsTypically losslessBut only limited manipulation is possible without expansionAudio/video compressionTypically lossy compression, with progressive refinementSometimes small fragments of signal can be reconstructed without reconstructing the wholeTime sequence is not audioTypically short and vary slowly with time


*Data Mining: Concepts and Techniques*Data CompressionOriginal DataCompressed DatalosslessOriginal DataApproximated lossy


*Data Mining: Concepts and Techniques*Dimensionality Reduction:Wavelet Transformation Discrete wavelet transform (DWT): linear signal processing, multi-resolutional analysisCompressed approximation: store only a small fraction of the strongest of the wavelet coefficientsSimilar to discrete Fourier transform (DFT), but better lossy compression, localized in spaceMethod:Length, L, must be an integer power of 2 (padding with 0s, when necessary)Each transform has 2 functions: smoothing, differenceApplies to pairs of data, resulting in two set of data of length L/2Applies two functions recursively, until reaches the desired length


*Data Mining: Concepts and Techniques*DWT for Image CompressionImage

Low Pass High Pass

Low Pass High Pass

Low Pass High Pass


*Data Mining: Concepts and Techniques*Given N data vectors from n-dimensions, find k n principal components that can be best used to represent data StepsNormalize input data: Each attribute falls within the same rangeCompute k orthonormal (unit) vectors, i.e., principal componentsEach input data (vector) is a linear combination of the k principal component vectorsThe principal components are sorted in order of decreasing significance or strengthSince the components are sorted, the size of the data can be reduced by eliminating the weak components, i.e., those with low variance. (i.e., using the strongest principal components, it is possible to reconstruct a good approximation of the original dataWorks for numeric data onlyUsed when the number of dimensions is large

Dimensionality Reduction: Principal Component Analysis (PCA)



X1X2Y1Y2Principal Component Analysis


*Data Mining: Concepts and Techniques*Numerosity ReductionReduce data volume by choosing alternative, smaller forms of data representationParametric methodsAssume the data fits some model, estimate model parameters, store only the parameters, and discard the data (except possible outliers)Example: Log-linear modelsobtain value at a point in m-D space as the product on appropriate marginal subspaces Non-parametric methods Do not assume modelsMajor families: histograms, clustering, sampling


*Data Mining: Concepts and Techniques*Data Reduction Method (1): Regression and Log-Linear ModelsLinear regression: Data are modeled to fit a straight lineOften uses the least-square method to fit the lineMultiple regression: allows a response variable Y to be modeled as a linear function of multidimensional feature vectorLog-linear model: approximates discrete multidimensional probability distributions


Linear regression: Y = w X + bTwo regression coefficients, w and b, specify the line and are to be estimated by using the data at handUsing the least squares criterion to the known values of Y1, Y2, , X1, X2, .Multiple regression: Y = b0 + b1 X1 + b2 X2.Many nonlinear functions can be transformed into the aboveLog-linear models:The multi-way table of joint probabilities is approximated by a product of lower-order tablesProbability: p(a, b, c, d) = ab acad bcd

Regress Analysis and Log-Linear Models

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*Data Mining: Concepts and Techniques*Data Reduction Method (2): HistogramsDivide data into buckets and store average (sum) for each bucketPartitioning rules:Equal-width: equal bucket rangeEqual-frequency (or equal-depth)V-optimal: with the least histogram variance (weighted sum of the original values that each bucket represents)MaxDiff: set bucket boundary between each pair for pairs have the 1 largest differences


*Data Mining: Concepts and Techniques*Data Reduction Method (3): ClusteringPartition data set into clusters based on similarity, and store cluster representation (e.g., centroid and diameter) onlyCan be very effective if data is clustered but not if data is smearedCan have hierarchical clustering and be stored in multi-dimensional index tree structuresThere are many choices of clustering definitions and clustering algorithmsCluster analysis will be studied in depth in Chapter 7


*Data Mining: Concepts and Techniques*Data Reduction Method (4): SamplingSampling: obtaining a small sample s to represent the whole data set NAllow a mining algorithm to run in complexity that is potentially sub-linear to the size of the dataChoose a representative subset of the dataSimple random sampling may have very poor performance in the presence of skewDevelop adaptive sampling methodsStratified sampling: Approximate the percentage of each class (or subpopulation of interest) in the overall database Used in conjunction with skewed dataNote: Sampling may not reduce database I/Os (page at a time)


*Data Mining: Concepts and Techniques*Sampling: with or without ReplacementSRSWOR(simple random sample without replacement)SRSWR


*Data Mining: Concepts and Techniques*Sampling: Cluster or Stratified Sampling

Raw Data Cluster/Stratified Sample


*Data Mining: Concepts and Techniques*DiscretizationThree types of attributes:Nominal values from an unordered set, e.g., color, professionOrdinal values from an ordered set, e.g., military or academic rank Continuous real numbers, e.g., integer or real numbersDiscretization: Divide the range of a continuous attribute into intervalsSome classification algorithms only accept categorical attributes.Reduce data size by discretizationPrepare for further analysis


*Data Mining: Concepts and Techniques*Discretization and Concept HierarchyDiscretization Reduce the number of values for a given continuous attribute by dividing the range of the attribute into intervalsInterval labels can then be used to replace actual data valuesSupervised vs. unsupervisedSplit (top-down) vs. merge (bottom-up)Discretization can be performed recursively on an attributeConcept hierarchy formationRecursively reduce the data by collecting and replacing low level concepts (such as numeric values for age) by higher level concepts (such as young, middle-aged, or senior)


*Data Mining: Concepts and Techniques*Discretization and Concept Hierarchy Generation for Numeric DataTypical methods: All the methods can be applied recursivelyBinning (covered above)Top-down split, unsupervised, Histogram analysis (covered above)Top-down split, unsupervisedClustering analysis (covered above)Either top-down split or bottom-up merge, unsupervisedEntropy-based discretization: supervised, top-down splitInterval merging by 2 Analysis: unsupervised, bottom-up mergeSegmentation by natural partitioning: top-down split, unsupervised


*Data Mining: Concepts and Techniques*Entropy-Based DiscretizationGiven a set of samples S, if S is partitioned into two intervals S1 and S2 using boundary T, the information gain after partitioning is

Entropy is calculated based on class distribution of the samples in the set. Given m classes, the entropy of S1 is

where pi is the probability of class i in S1The boundary that minimizes the entropy function over all possible boundaries is selected as a binary discretizationThe process is recursively applied to partitions obtained until some stopping criterion is metSuch a boundary may reduce data size and improve classification accuracy


*Data Mining: Concepts and Techniques*Interval Merge by 2 AnalysisMerging-based (bottom-up) vs. splitting-based methodsMerge: Find the best neighboring intervals and merge them to form larger intervals recursivelyChiMerge [Kerber AAAI 1992, See also Liu et al. DMKD 2002]Initially, each distinct value of a numerical attr. A is considered to be one interval2 tests are performed for every pair of adjacent intervalsAdjacent intervals with the least 2 values are merged together, since low 2 values for a pair indicate similar class distributionsThis merge process proceeds recursively until a predefined stopping criterion is met (such as significance level, max-interval, max inconsistency, etc.)


*Data Mining: Concepts and Techniques*Segmentation by Natural PartitioningA simply 3-4-5 rule can be used to segment numeric data into relatively uniform, natural intervals.If an interval covers 3, 6, 7 or 9 distinct values at the most significant digit, partition the range into 3 equi-width intervalsIf it covers 2, 4, or 8 distinct values at the most significant digit, partition the range into 4 intervalsIf it covers 1, 5, or 10 distinct values at the most significant digit, partition the range into 5 intervals


*Data Mining: Concepts and Techniques*Example of 3-4-5 Rule

(-$400 -$5,000)Step 4:


*Data Mining: Concepts and Techniques*Concept Hierarchy Generation for Categorical DataSpecification of a partial/total ordering of attributes explicitly at the schema level by users or expertsstreet < city < state < countrySpecification of a hierarchy for a set of values by explicit data grouping{Urbana, Champaign, Chicago} < IllinoisSpecification of only a partial set of attributesE.g., only street < city, not othersAutomatic generation of hierarchies (or attribute levels) by the analysis of the number of distinct valuesE.g., for a set of attributes: {street, city, state, country}


*Data Mining: Concepts and Techniques*Automatic Concept Hierarchy GenerationSome hierarchies can be automatically generated based on the analysis of the number of distinct values per attribute in the data set The attribute with the most distinct values is placed at the lowest level of the hierarchyExceptions, e.g., weekday, month, quarter, year


*Data Mining: Concepts and Techniques*SummaryData preparation or preprocessing is a big issue for both data warehousing and data miningDiscriptive data summarization is need for quality data preprocessingData preparation includesData cleaning and data integrationData reduction and feature selectionDiscretizationA lot a methods have been developed but data preprocessing still an active area of research


*Data Mining: Concepts and Techniques*ReferencesD. P. Ballou and G. K. Tayi. Enhancing data quality in data warehouse environments. Communications of ACM, 42:73-78, 1999T. Dasu and T. Johnson. Exploratory Data Mining and Data Cleaning. John Wiley & Sons, 2003T. Dasu, T. Johnson, S. Muthukrishnan, V. Shkapenyuk. Mining Database Structure; Or, How to Build a Data Quality Browser. SIGMOD02. H.V. Jagadish et al., Special Issue on Data Reduction Techniques. Bulletin of the Technical Committee on Data Engineering, 20(4), December 1997D. Pyle. Data Preparation for Data Mining. Morgan Kaufmann, 1999E. Rahm and H. H. Do. Data Cleaning: Problems and Current Approaches. IEEE Bulletin of the Technical Committee on Data Engineering. Vol.23, No.4V. Raman and J. Hellerstein. Potters Wheel: An Interactive Framework for Data Cleaning and Transformation, VLDB2001T. Redman. Data Quality: Management and Technology. Bantam Books, 1992Y. Wand and R. Wang. Anchoring data quality dimensions ontological foundations. Communications of ACM, 39:86-95, 1996R. Wang, V. Storey, and C. Firth. A framework for analysis of data quality research. IEEE Trans. Knowledge and Data Engineering, 7:623-640, 1995




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missing data

data preprocessingwhy

data cubes

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incomplete data

data dirty

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data warehousedata mining