UNIT 4 Characterization and Comparison

Transcription

1 UNIT 4 Characterization and Comparison Lecture Topic ************************************************* Lecture 22 Lecture 23 Lecture 24 Lecture 25 Lecture 26 What is concept description? Data generalization and summarization based characterization Analytical characterization: Analysis of attribute relevance Mining class comparisons: Discriminating between different classes Mining descriptive statistical measures in large databases 1

2 Lecture 22 What is Concept Description? 2

3 What is Concept Description? Descriptive vs. predictive data mining Descriptive mining: describes concepts or task relevant data sets in concise, summarative, informative, discriminative forms Predictivemining: Basedon data and analysis, constructs models for the database, and predicts the trend and properties of unknown data Concept description: Characterization: provides a concise and succinct summarization ation of the given collection of data Comparison: provides descriptions comparing two or more collections of data 3 Lecture 22 What is Concept Description?

4 Concept Description vs. OLAP Concept description: can handle complex data types of the attributes and their aggregations a more automated t process OLAP: restricted to a small number of dimension and measure types user controlled process 4 Lecture 22 What is Concept Description?

5 Lecture 23 Data generalization and summarizationbased characterization 5

6 Data Generalization and Summarization based Characterization Dt Data generalization A process which abstracts a large set of task relevant data in a database from a lowconceptual levels to higher ones Approaches: Data cube approach(olap approach) Attribute oriented induction approach 4 5 Conceptual levels Lecture 23 Data generalization and summarization based characterization 6

7 Characterization: Data Cube Approach Perform computations and store results in data cubes Strength An efficient implementation of data generalization Computation of various kinds of measures count( ), sum( ), average( g(), max( ) Generalization and specialization can be performed on a data cube by roll up and drill down Limitationsit ti handle only dimensions of simple nonnumeric data and measures of simple aggregated numeric values. Lack of intelligent analysis, can t tell which dimensions should be used and what levels should the generalization reach 7 Lecture 23 Data generalization and summarization based characterization

8 Attribute Oriented Induction Proposed din 1989 (KDD 89 workshop) kh Not confined to categorical data nor particular measures. How it is done? Collect the task relevant data( initial relation) using a relational database query Perform generalization by attribute removal or attribute generalization. Apply aggregation by merging identical, generalized tuples and accumulating their respective counts. Interactive presentation with users. 8 Lecture 23 Data generalization and summarization based characterization

9 Data focusing Basic Principles of Attribute Oriented Induction task relevant data, including dimensions, andtheresult is theinitial relation. Attribute removal remove attribute A if there is a large set of distinct values for A but (1) there is no generalization operator on A, or (2) A s higher h level lconcepts are expressed in terms of other attributes. t 9 Lecture 23 Data generalization and summarization based characterization

10 Basic Principles of Attribute Oriented Induction Attribute generalization If there is a large set of distinct values for A, and there exists a set of generalization operators on A, then select an operator and generalize A. Attribute threshold h control Generalized relation threshold control control the final relation/rule size. 10 Lecture 23 Data generalization and summarization based characterization

11 Basic Algorithm for Attribute Oriented e tedinduction Initial Relation Query processing of task relevant data, deriving the initial relation. Pre Generalization Basedonthe analysis of the number of distinct values in each attribute, determine generalization plan for each attribute: removal? or how high to generalize? 11 Lecture 23 Data generalization and summarization based characterization

12 Basic Algorithm for Attribute Oriented Induction Prime Generalization Based on the PreGen plan, perform generalization to the right level to derive a prime generalized relation, accumulating the counts. Presentation User interaction: (1) adjust levels by drilling, (2) pivoting, (3) mapping into rules, cross tabs, visualization presentations. 12 Lecture 23 Data generalization and summarization based characterization

13 13 Example DMQL: Describe general characteristics of graduate students in the Big University database use Big_University_DB mine characteristics as Science_Students in relevance to name, gender, major, birth_place, birth_date, residence, phone#, gpa from student where status in graduate Corresponding SQL statement: Select name, gender, major, birth_place, birth_date, residence, phone#, gpa from student where status in { Msc, MBA, PhD } Lecture 23 Data generalization and summarization based characterization

14 Class Characterization: An Example Initial Relation Name Gender Major Birth-Place Birth_date Residence Phone # GPA Jim M CS Vancouver,BC, Main St., Woodman Canada Richmond Scott M CS Montreal, Que, st Ave., Lachance Canada Richmond Laura Lee F Physics Seattle, WA, USA Austin Ave., Burnaby Removed Retained Sci,Eng, Bus Country Age range City Removed Excl, VG,.. Gender Major Birth_region Age_range Residence GPA Count i M Science Canada Richmond Very-good 16 F Science Foreign Burnaby Excellent 22 Prime Generalized Relation 14 Gender Birth_Region Canada Foreign Total M F Total Lecture 23 Data generalization and summarization based characterization

15 Generalized relation Presentation of Generalized Results Relations where some or all attributes are generalized, with counts or other aggregation values accumulated. ltd Cross tabulation Mapping results into cross tabulation form (similar to contingency tables). Visualization techniques: Pie charts, bar charts, curves, cubes, and other visual forms. Quantitative characteristic rules Mapping generalized result into characteristic rules with quantitative information associated withit it, 15 grad ( x) male( x) birth _ region( x) " Canada"[ t:53%] birth _ region( x) " foreign"[ t:47%]. Lecture 23 Data generalization and summarization based characterization

16 Presentation Generalized Relation 16 Lecture 23 Data generalization and summarization based characterization

17 Presentation Crosstab 17 Lecture 23 Data generalization and summarization based characterization

18 Implementation by Cube Technology Construct a data cube on the fly for the given data mining query Facilitate efficient drill down analysis May increase the response time A balanced solution: precomputation of subprime relation Use a predefined & precomputed data cube Construct a data cube beforehand Facilitate not only the attribute oriented induction, but also attribute relevance analysis, dicing, slicing, roll up and drill down Cost of cube computation and the nontrivial storage overhead 18 Lecture 23 Data generalization and summarization based characterization

19 Lecture 24 Analytical characterization: Analysis of attribute relevance 19

20 Similarity: Characterization vs. OLAP Presentation ti of dt data summarization at multiple l levels l of abstraction. Interactivedrilling drilling, pivoting, slicing and dicing. Differences: Automated desired level allocation. Dimension relevance analysis and ranking when there are many relevant dimensions. Sophisticated typing on dimensions and measures. Analytical characterization: data dispersion analysis. 20 Lecture 24 Analytical characterization: Analysis of attribute relevance

21 Why? Attribute Relevance Analysis Which dimensions should be included? How high level of generalization? Automatic vs. interactive Reduce # attributes; easy to understand patterns What? statistical method for preprocessing data filter out irrelevant or weakly relevant attributes retain orrankrank therelevant attributes relevance related to dimensions and levels analytical characterization, analytical comparison 21 Lecture 24 Analytical characterization: Analysis of attribute relevance

22 Attribute relevance analysis Data Collection Analytical Generalization Use information gain analysis to identify highly relevant dimensions and levels. Relevance Analysis Sort and select the most relevant dimensions and levels. Attribute oriented Induction for class description Onselected dimension/level OLAP operations (drilling, slicing) on relevance rules 22 Lecture 24 Analytical characterization: Analysis of attribute relevance

23 Relevance Measures Quantitative relevance measure determines the classifying i power of an attribute within ihi a set of data. Methods information gain (ID3) gain ratio (C4.5) gini index 2 contingency table statistics uncertainty coefficient 23 Lecture 24 Analytical characterization: Analysis of attribute relevance

24 Decision tree Information Theoretic Approach each internal node tests an attribute each branch corresponds to attribute value each leaf node assigns a classification ID3 algorithm build decision tree based on training objects with known class labels to classify testing objects rank attributes with information gain measure minimal height the least number of tests to classify an object 24 Lecture 24 Analytical characterization: Analysis of attribute relevance

25 Top Down Induction of Decision Tree Attributes = {Outlook, Temperature, Humidity, Wind} PlayTennis = {yes, no} Outlook sunny overcast rain high Humidity normal yes strong Wind weak no yes no yes 25 Lecture 24 Analytical characterization: Analysis of attribute relevance

26 Entropy and Information Gain S contains s i tuples of class C i for i = {1,, m} Informationmeasuresmeasures info required to classifyany any arbitrary tuple m si si Entropy of attribute I( s1,s2,...,s A mwith ) values log 2 {a 1,a 2,,a v } i 1 s s v s... s 1j mj E(A) I( s1 j,...,s mj) Informationgained j 1 by s branching on attribute A Gain(A) I(s 1,s 2,..., sm) E(A) 26 Lecture 24 Analytical characterization: Analysis of attribute relevance

27 Task Example: Analytical Characterization Mine general characteristics describing graduate students using analytical characterization Given attributes name, gender, major, birth_place, birth_date, phone#, and gpa Gen(a i ) = concept hierarchies on a i U i = attribute analytical thresholds for a i T i = attribute generalization thresholds for a i R = attribute relevance threshold 27 Lecture 24 Analytical characterization: Analysis of attribute relevance

28 Example: Analytical Characterization 1. Data collection target class: graduate student contrasting class: undergraduate student 2. Analytical generalization using U i attribute removal remove name and phone# attribute generalization generalize major, birth_place, birth_date andgpa accumulate counts candidate relation: gender, major, birth_country, age_range and gpa 28 Lecture 24 Analytical characterization: Analysis of attribute relevance

29 Example: Analytical characterization gender major birth_country age_range gpa count M Science Canada Very_good 16 F Science Foreign Excellent 22 M Engineering Foreign Excellent 18 F Science Foreign Excellent 25 M Si Science Canada Excellent 21 F Engineering Canada Excellent 18 Candidate relation for Target class: Graduate students ( =120) gender major birth_country age_range gpa count M Science Foreign <20 Very_good 18 F Business Canada <20 Fair 20 M Business Canada <20 Fair 22 F Science Canada Fair 24 M Engineering Foreign Very_good 22 F Engineering Canada <20 Excellent Candidate relation for Contrasting class: Undergraduate students ( =130) Lecture 24 Analytical characterization: Analysis of attribute relevance

30 Example: Analytical characterization 3. Relevance analysis Calculate expected info required to classify an arbitrary tuple I(s ) I( 120, 130 ) log 2 log ,s 2. Calculate entropy of each attribute: e.g. major For major= Science : S 11 =84 S 21 =42 I(s 11,s 21 )= For major= Engineering : S 12 =36 S 22 =46 I(s 12,s 22 )= For major= Business : S 13 =0 S 23 =42 I(s 13,s 23 )=0 Number of grad students t in Science Number of undergrad students in Science 30 Lecture 24 Analytical characterization: Analysis of attribute relevance

31 Example: Analytical Characterization Calculate expected info required to classify a given sample if S is partitioned according to the attribute E(major) I( s Gain(major) 82 ) I( s ) I( s ,s21 12,s22 13,s23. I(s 1,s 2 ) E(major) ) Calculate information gain for each attribute Information gain for all attributes Gain(gender) = Gain(birth_country) = Gain(major) = Gain(gpa) = Gain(age_range) = Lecture 24 Analytical characterization: Analysis of attribute relevance

32 Example: Analytical characterization 4. Initial working relation (W 0 0) derivation R = 0.1 remove irrelevant/weakly relevant attributes from candidate relation => drop gender,, birth_country remove contrasting class candidate relation major age_range gpa count Science Very_good 16 Science Excellent 47 Science Excellent 21 Engineering Excellent 18 Engineering Excellent 18 Initial target class working relation W 0 : Graduate students 5. Perform attribute oriented induction on W 0 using T i 32 Lecture 24 Analytical characterization: Analysis of attribute relevance

33 Lecture 25 Mining class comparisons: Discriminating between different classes 33

34 Comparison Mining Class Comparisons Comparing two or more classes. Method Partition the set of relevant data into the target class and the contrasting classes Generalize both classes to the same high level concepts Compare tuples with the same high level descriptions Lecture 25 Mining class comparisons: Discriminating between different classes 34

35 Mining Class Comparisons Present for every tuple its description and two measures: support distribution within single class comparison distribution between classes Highlight the tuples with strong discriminant features Relevance Analysis Find attributes (features) which best distinguish different classes. Lecture 25 Mining class comparisons: Discriminating between different classes 35

36 Example: Analytical comparison Task Comparegraduate and undergraduate students using discriminant rule. DMQL query use Big_University_DB mine comparison as grad_vs_undergrad_students in relevance to name, gender, major, birth_place, birth_date, residence, phone#, gpa for graduate_students where status in graduate versus undergraduate_students where status in undergraduate analyze count% from student t Lecture 25 Mining class comparisons: Discriminating between different classes 36

37 Given Example: Analytical comparison attributes name, gender, major, birth_place, birth_date, residence, phone# and gpa Gen(a i ) = concept hierarchies on attributes a i U i = attribute analytical thresholds for attributes a i T i = attribute generalization thresholds for attributes a i R = attribute relevance threshold Lecture 25 Mining class comparisons: Discriminating between different classes 37

38 Example: Analytical comparison 1. Data collection target and contrasting classes 2. Attribute relevance analysis remove attributes name, gender, major, phone# 3. Synchronous generalization controlled by user specified dimension thresholds prime target and contrasting classes relations/cuboids Lecture 25 Mining class comparisons: Discriminating between different classes 38

39 Example: Analytical comparison Birth_country Age_range Gpa Count% Canada Good 5.53% Canada Good 2.32% Canada Over_30 Very_good 5.86% Other Over_30 Excellent 4.68% Prime generalized relation for the target class: Graduate students Birth_country Age_range Gpa Count% Canada Fair 5.53% Canada Good 4.53% Canada Good 5.02% Other Over_30 Excellent 068% 0.68% Prime generalized relation for the contrasting class: Undergraduate students Lecture 25 Mining class comparisons: Discriminating between different classes 39

40 Example: Analytical comparison 4. Drill down, roll up and other OLAP operations on target and contrasting classes to adjust levels of abstractions of resulting description 5. Presentation as generalized relations, crosstabs, bar charts, pie charts, or rules contrasting measures to reflect comparison between target and contrasting classes count% Lecture 25 Mining class comparisons: Discriminating between different classes 40

41 Quantitative Discriminant Rules Cj = target class q a = a generalized tuple covers some tuples of class but can also cover some tuples of contrasting class d weight range: [0, 1] d weight ih count(q a C j ) quantitative discriminant i i rule form m i 1 count(q a C i ) X, target_class(x) condition(x) [d : d_weight] Lecture 25 Mining class comparisons: Discriminating between different classes 41

42 Example: Quantitative Discriminant Rule Status Birth_country Age_range Gpa Count Graduate Canada Good 90 Undergraduate Canada Good 210 Count distribution ib i between graduate and undergraduate d students for a generalized tuple Quantitative discriminant rule X, graduate_ student( X) birth_ country ( X ) " Canada" age_ range ( X ) "25 30" gpa ( X ) " good" where 90/(90+120) = 30% [ d :30%] Lecture 25 Mining class comparisons: Discriminating between different classes 42

43 Class Description Quantitative characteristic rule X, target_class(x) necessary condition(x) Quantitative discriminant rule X, target_class(x) condition(x) sufficient i Quantitative description rule X, condition target_cla ss(x) necessary and sufficient [t : t_weight] [d : d_weight] (X)[t : w 1,d : w 1]... condition n(x) [t : w n, d : w n] 1 Lecture 25 Mining class comparisons: Discriminating between different classes 43

44 Example: Quantitative Description Rule Location/item TV Computer Both_items Count t-wt d-wt Count t-wt d-wt Count t-wt d-wt Europe 80 25% 40% % 30% % 32% N_Am % 60% % 70% % 68% Both_ regions % 100% % 100% % 100% Crosstab showing associated t-weight, d-weight values and total number (in thousands) of TVs and computers sold at AllElectronics in 1998 Quantitative a description rule for target class Europe uope X,Europe(X) (item(x) " TV" ) [t : 25%,d : 40%] (item(x) " computer" ) [t : 75%,d :30%] Lecture 25 Mining class comparisons: Discriminating between different classes 44

45 Lecture 26 Mining descriptive statistical measures in large databases 45

46 Mining Data Dispersion Characteristics Motivation To better understand the data: central tendency, variation and spread Data dispersion characteristics median, max, min, quantiles, outliers, variance, etc. Numerical dimensions correspond to sorted intervals Data dispersion: analyzed with multiple granularities of precision Boxplot or quantile analysis on sorted intervals Dispersion analysis on computed measures Folding measures into numerical dimensions Boxplot or quantile analysis on the transformed cube 46 Lecture 26 Mining descriptive statistical measures in large databases

47 Measuring the Central Tendency 1 Mean x n n i 1 x i Weighted arithmetic mean Median: A holistic measure x n i 1 n i 1 w i w x i i Middle value if odd number of values, or average of the middle two values otherwise estimated by interpolation Mode Value that occurs most frequently in the data n / 2 ( f ) l median L1 ( ) c f median Unimodal, bimodal, trimodal Empirical formula: mean mode 3 ( mean median ) 47 Lecture 26 Mining descriptive statistical measures in large databases

48 Measuring the Dispersion of Data Quartiles, outliers and boxplots Quartiles: Q th th 1 (25 percentile), Q 3 (75 percentile) Inter quartile range: IQR = Q 3 Q 1 Five number summary: min, Q 1, M, Q 3, max Boxplot: ends of the box are the quartiles, median is marked, whiskers, and plot outlier individually Outlier: usually, a value higher/lower than1 1.5 x IQR Variance and standard deviation Variance s 2 : (algebraic, scalable computation) s 2 n 1 1 n i 1 ( x i x ) 2 n n 2 x i ( i 1 n i 1 Standard deviation s is the square root of variance s 2 n 1 1 [ 1 x i ) 2 ] 48 Lecture 26 Mining descriptive statistical measures in large databases

49 Boxplot Analysis Five number summaryof a distribution: Boxplot Minimum, Q1, M, Q3, Maximum Data is represented with a box The ends of the box are at the first and third quartiles, i.e., the height of the box is IRQ The median is marked by a line within the box Whiskers: two lines outside the box extend to Minimum i and Maximum 49 Lecture 26 Mining descriptive statistical measures in large databases

50 A Boxplot A boxplot 50 Lecture 26 Mining descriptive statistical measures in large databases

51 Visualization of Data Dispersion: Boxplot Analysis 51 Lecture 26 Mining descriptive statistical measures in large databases

52 Mining Descriptive Statistical Measures in Large Databases Variance s 2 1 n 1 i i n 1 i 1 n 1 n ( x x) x x i 2 Standarddeviation: deviation: the square root of the variance Measures spread about the mean It is zero if and only if all the values are equal Both the deviation and the variance are algebraic 52 Lecture 26 Mining descriptive statistical measures in large databases

53 Histogram Analysis Graph displays of basic statistical class descriptions Frequency histograms A univariate graphical method Consists of a set of rectangles that reflect the counts or frequencies of the classes present in the given data 53 Lecture 26 Mining descriptive statistical measures in large databases

54 Quantile Plot Displays all of the data (allowing the user to assess both the overall behavior and unusual occurrences) Plots quantile information For a data x i data sorted in increasing order, f i indicates that approximately 100 f i % of the data are below or equal to the value x i 54 Lecture 26 Mining descriptive statistical measures in large databases

55 Quantile Quantile (Q Q) Plot Graphs the quantiles of one univariate distribution against the corresponding quantiles of another Allows the user to view whether h there is a shift in going from one distribution to another Lecture 26 Mining descriptive statistical measures in large databases 55

56 Scatter plot Provides a first look at bivariate data to see clusters of points, outliers, etc Each pair of values is treated as a pair of coordinates and plotted as points in the plane 56 Lecture 26 Mining descriptive statistical measures in large databases

57 Loess Curve Adds a smooth curve to a scatter plot in order to provide better perception of the pattern of dependence Loess curve is fitted by setting two parameters: a smoothing parameter, and the degree of the polynomials that are fitted by the regression 57 Lecture 26 Mining descriptive statistical measures in large databases

58 Histogram Boxplot Graphic Displays of Basic Statistical Descriptions Quantile plot: each value x i is paired with f i indicating that approximately 100 f i % of data are x i Quantile quantile (q q) plot: graphs the quantiles of one univariant distribution against the corresponding quantiles of another Scatter plot: each pair of values is a pair of coordinates and plotted as points in the plane Loess (local regression) curve: add a smoothcurve to a scatter plot to provide better perception of the pattern of dependence 58 Lecture 26 Mining descriptive statistical measures in large databases

59 AO Induction vs. Learning from example Paradigm Difference inphilosophies and basic assumptions Positive and negative samples in learning from example: positive used for generalization, negative for specialization Positive ii samples only in data mining: i hence generalization based, i to drill down backtrack the generalization to a previous state Difference in methods of generalizations Machine learning generalizes on a tuple by tuple basis Data mining generalizes on an attribute by attribute basis 59 Lecture 26 Mining descriptive statistical measures in large databases

60 Comparison of Entire vs. Factored Version Space 60 Lecture 26 Mining descriptive statistical measures in large databases

61 Incremental and Parallel Mining of Concept tdescription Incremental mining: revision based on newly added data DB Generalize DB to the same level of abstraction in the generalized relation R to derive R Union R U R, i.e., merge counts and other statistical information to produce a new relation R Similar philosophy can be applied to data sampling, parallel and/or distributed mining, etc. 61 Lecture 26 Mining descriptive statistical measures in large databases