CSE5230 - Data Mining, 2001Lecture 8.1 Data Mining - CSE5230 Data Mining and Information Visualization CSE5230/DMS/2001/8

CSE5230 - Data Mining, 2001 Lecture 8.1

Data Mining - CSE5230

Data Mining and Information Visualization

CSE5230/DMS/2001/8


Lecture Outline

Overview of information visualization The role of visualization in the process of data

mining The patterns being sought: clusters and outliers Issues when visualizing higher dimensional

relationships Criteria for comparison A range of visualization techniques for

exploratory data analysis


Information Visualization

A conjunction of a number of fields: Data Mining Cognitive Science Graphic Design Interactive Computer Graphics

Information Visualization attempts to use visual approaches and dynamic controls to provide understanding and analysis of multidimensional data

The data may have no inherent 2D or 3D semantics and may be abstract in nature. There is no underlying physical model. Much of the data in databases is of this type


Role of Information Visualization

Acts as an exploratory tool Useful for identifying subsets of the data Structures, trends and outliers may be

identified Statistical tests tend incorporate isolated

instances into a broader model as they attempt to formulate global features

There is no requirement for an hypothesis, but the techniques can also support the formulation of hypotheses if wanted


Integrating Visualization withData Mining

There are four possible approaches: Use the visualization technique to present the results of

the data mining process Use visualization techniques as complements to the

data mining process. They complement and increase understanding in a passive way.

Use visualization techniques to steer the data mining process. The visualization aids in deciding the appropriate data mining technique to use and appropriate subsets of the data to consider.

Apply data mining techniques to the visualization rather than directly to the data. The idea is to capture the essential semantics visually then apply the data mining tools.


The Process of Knowledge Discovery in Databases (a.k.a. Data Mining)

Data Cleaning & Enrichment

Coding Data mining Reportingselection

-domain consistency- clustering

- segmentation-de-duplication - prediction-disambiguation

Requirement Action

Feedback

Operational data External data

The Knowledge Discovery in Databases (KDD) process (AdZ1996)

Information


Visualization in the Context of theData Mining Process

Visualization tools can potentially be used at a number of steps in the DM process. But: the same tools may not be appropriate at each step how they will be used may be different

In general, it is not important whether data visualization is the first step in the process or not the feedback loop which moves the process forward may be

commenced by either a visualization or a query

some visualizations, (e.g. see slide 25) require an initial query to generate a visualization this is an example of a complementary approach

» questions generate visualizations, which may prompt further questions or generate hypotheses


Motivations for Visualization

The human visual system is extremely good at recognizing patterns it is quicker and easier to understand visual representations than to

absorb information from language or formal notations.

Exploratory visualization assists in: identifying areas of interest identifying questions which might usefully be asked

i.e. a relevant or revealing visualization of either part or all of a data set, may suggest useful questions and/or hypotheses to the analyst. These can then be confirmed by more rigorous approaches e.g. some clustering techniques require an initial estimate of the

number of clusters present in the data

» visualization techniques can assist in this estimation


Criteria for Comparison of Visualization Tools

Number of dimensions that can be represented Number of data items that can be handled Ability to handle categorical and other non-

numeric data types Ability to reveal patterns Ease of use Learning Curve (to what degree is the technique

intuitive)


Examples - Scatterplot

Each pair of features (i.e. fields of records) in a multidimensional database is graphed as a point in two dimensions (2D) This straightforward graphing procedure produces a

simple scatterplot - a projection of the multidimensional data into 2D

The scatterplots of all pair-wise combinations of features are arranged in a matrix The figure on the following slide illustrates a scatter plot

matrix of 3D from a study of abrasion loss in tyres. The features are hardness, tensile-strength, abrasion-loss [Tie1989]

Each “sub-graph” gives insight into the relationship between a pair of features


Scatterplot Matrix

Scatterplot matrix of abrasion loss data [Tie1989]


Possible Problems with Scatterplots

Everitt [Eve78, p. 5] gives two reasons why scatter plots can prove unsatisfactory: if number of features is greater than ~10, the number of

plots to be examined is very large

» this is just as likely to lead to confusion as to knowledge of the structures in the data.

structures existing in multidimensional data set do not necessarily appear in the 2D projections of the features represented in scatterplots (see next slide)

Despite these potential problems, variations on the scatterplot approach are the most commonly used of all the visualization techniques


Scatterplots: recognizing high-dimensional structures - 1

A structure which appears as a cluster in a 2D projection may in fact be a “pipe” in 3D a pipe is a structure in 3D that looks like a rod or pipe when viewed

in a 3D representation

While the pipe is easily identifiable in a 3D display only projections of it will appear in the 2D components of the scatterplot matrix depending of the orientation of the pipe in 3D, it may not appear as

an obvious cluster, if at all

Equivalent structures can exist in higher dimensions, e.g. a cluster in 5D might be a “pipe” in 6D the appearance of high-D structures in lower-D projections

depends on the luck and skill of the analyst in choosing the projections, and on the alignment of the structures to the axes


Scatterplots: recognizing high-dimensional structures - 2

Random(Uniform) May be a plane in 3D

A cluster in 2D May be a pipe in 3D(or a cluster in 3D)


Example Tool: Spotfirehttp://www.spotfire.com/


Example Tool: Spotfirehttp://www.spotfire.com/

The user interacts with data by choosing which features will form the horizontal and vertical axes

Other features can represented by color this is an example of using the richness of visual representations

to provide more information to the user. As well as 2D spatial position, other modes such as colour, size, shape and even sound can be used to convey information about high-dimensional data

On the previous slide, the data set contains a 3D cluster in a 4D space (i.e. there are four features) There are also some background “noise” instances

The cluster can seen, with its centre at around (20, 74) all the points in the cluster are red, showing that it’s a 3D cluster


Example Tool: DBMinerhttp://www.dbminer.com/


Example Tool: DBMinerhttp://www.dbminer.com/

DBMiner is an integrated data mining tool It employs a data visualization known as a “data

cube” (see On-Line Analytic Processing - OLAP) After creating a data cube, user can apply a

variety of data mining techniques to analyze the data further, including: association, classification, prediction and clustering,

etc.

The figure on the preceding slide shows a data cube for a data set which has 3D cluster of data instances in a 3D space


Examples: Parallel Coordinates - 1

Uses the idea of mapping a point in a multidimensional feature space on to a number of parallel axes

Each feature is mapped one axis as many axes as need can be lined up side to side there is no limit to the number of dimensions that can

be represented

A single polygonal line connects the individual coordinate mappings for each point

The technique has been applied in air traffic control, robotics, computer vision and computational geometry



Parallel axes for RN. The polygonal line shown represents the point C= (C1, .... , C i-1, Ci, Ci+1, ... , Cn)

C1Cn

X1 X2 X3 Xi-1 Xn

Ci-1

Ci-1

Ci



The Parallel Coordinates visualization technique is employed in the software WinViz http://www.computer.org/intelligent/ex1996/x5069abs.htm

The main advantage of the technique is that it can represent unlimited numbers of dimensions

When many points are represented using the parallel coordinates, the overlap of the polygonal lines can make it difficult to identify structures in the data.

Certain structures, such as clusters, can often be identified but others are hidden due to the overlap.


Two Clusters In WinViz


Examples: Stick Figures

The stick figure technique is intended to make use of the user’s low-level perceptual processes [PGL1995], such as perception of: texture, color, motion, and depth

The hope is that the user will “automatically” try to make physical sense of the pictures of the data created

Visualizations which represent multidimensional feature spaces by using a number of subspaces of 3D or less (e.g. scatterplots) rely more on our cognitive abilities than our perceptual abilities

Stick figures avoid this, and present all variables and data points in a single representation.


Iconographic display using stick figures -

US Census Data

http://ivpr.cs.uml.edu/gallery/


Examples: Pixel-based techniqueshttp://www.dbs.informatik.uni-muenchen.de/dbs/projekt/visdb/visdb.html

Query-Dependent Pixel-based Techniques based on a query, a “semantic distance” is calculated

between each of the query feature values and the features of each instance in the DB.

overall distance between the data values for a specific instance and the data attribute values used in the predicate of the query is also calculated

if an feature value for a specific instance matches the query it is assigned a colour indicating a match

» e.g. a sequence of colours starting from yellow and ending in black could be used, where black is assigned if none of the instance features match

Instances are arranged on the screen, with the data items with highest relevance in the centre of the display, and then proceeding outwards in a spiral


Examples: Worlds within Worldshttp://www.cs.columbia.edu/graphics/projects/AutoVisual/AutoVisual.html

Employs virtual reality devices to represent an nD virtual world in 3D or 4D-Hyperworlds basic approach to reducing the complexity of a

multidimensional function is to hold one or more of its independent variables constant

» equivalent to taking an infinitely thin slice of the world perpendicular to the constant variable’s axis

can be repeated until there are 3 dimensions and the resulting slice can be manipulated and displayed with conventional 3D graphics hardware

After reducing the higher-dimensional space to 3 dimensions the additional dimensions can be added back, by adding additional 3D worlds within the first 3D world


Dynamic Techniques

Allow interaction with the visualization to explore the data more effectively. Can potentially be applied to all visualization techniques Dynamic linking of the data attributes to the parameters

of the visualization. Filtering Linking and “brushing” between multiple visualizations Zooming Details on demand


Other Techniques

Keim and Kriegel’s query independent approach Chernoff faces

http://www.fas.harvard.edu/~stats/Chernoff/Hcindex.htm

Cone trees Perspective walls Visualization Spreadsheet A number of techniques especially developed for

web pages and their links


References [AdZ1996] P. Adriaans and D. Zantinge. Data Mining. Addison-Wesley, 1996. [BeS1997] A. Berson & S. J. Smith, Data Warehousing, Data Mining and OLAP,

McGraw-Hill, 1997 [Eve1978] B. S. Everitt, Graphical Techniques for Multivariate Data, Heinemann

Educational Books Ltd., London, 1978 [Thu1999] B. Thuraisingham, Data Mining: Technologies, Techniques, Tools, and

Trends, CRC Press LLC, Boca Raton, Florida 1999 [Tie1989] L. Tierney, XLISP-STAT: A Statistical Environment Based on the XLISP

Language (Version 2.0), University of Minnesota School of Statistics, Technical Report Number 528, July 1989

[PGL1995] R. M. Pickett, G. Grinstein,H. Levkowitz and S. Smith, Harnessing Preattentive Perceptual Processes in Visualization, pp. 9-21 in Perceptual Issues in Visualization(Eds. G. Grinstein & H. Levkowitz), Springer-Verlag, Berlin, 1995

[WGL1996] Database issues for data visualization, Proceedings of the IEEE Visualization '95 Workshop, A. Wierse, G. G. Grinstein and U. Lang, (eds), Atlanta, Georgia, USA, October 28, 1995

[LeG1993] Database issues for data visualization, Proceedings of the IEEE Visualization '93 Workshop, J. P. Lee and G. G. Grinstein, (eds), San Jose, California, USA, October 26, 1993

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CSE5230 - Data Mining, 2001Lecture 8.1 Data Mining - CSE5230 Data Mining and Information Visualization CSE5230/DMS/2001/8