Non-traditional Analysis The traditional statistical approach is based on a hypothesize-and-test paradigm. In other words, a hypothesis is proposed, an experiment is designed to gather the data, and then the data is analyzed with respect to the hypothesis. Unfortunately, this process is extremely labor- intensive. Current data analysis tasks often require the generation and evalu- ation of thousands of hypotheses, and consequently, the development of some data mining techniques has been motivated by the desire to automate the process of hypothesis generation and evaluation. Furthermore, the data sets analyzed in data mining are typically not the result of a carefully designed
6 Chapter 1 Introduction
experiment and often represent opportunistic samples of the data, rather than
random samples. Also, the data sets frequently involve non-traditional types
of data and data distributions.
1.3 The Origins of Data Mining
Brought together by the goal of meeting the challenges of the previous sec-
tion, researchers from different disciplines began to focus on developing more
efficient and scalable tools that could handle diverse types of data. This work,
which culminated in the field of data mining, built upon the methodology and
algorithms that researchers had previously used. In particular, data mining
draws upon ideas, such as (1) sampling, estimation, and hypothesis testing
from statistics and (2) search algorithms, modeling techniques, and learning
theories from artificial intelligence, pattern recognition, and machine learning.
Data mining has also been quick to adopt ideas from other areas, including
optimization, evolutionary computing, information theory, signal processing,
visualization, and information retrieval. A number of other areas also play key supporting roles. In particular,
database systems are needed to provide support for efficient storage, index-
ing, and query processing. Techniques from high performance (parallel) com-
puting are often important in addressing the massive size of some data sets.
Distributed techniques can also help address the issue of size and are essential
when the data cannot be gathered in one location. Figure 1.2 shows the relationship of data mining to other areas.
Figure 1.2. Data mining as a conlluence of many disciplines.
Data Mining Tasks 7
Data mining tasks are generally divided into two major categories:
Predictive tasks. The objective of these tasks is to predict the value of a par- ticular attribute based on the values of other attributes. The attribute to be predicted is commonly known as the target or dependent vari- able, while the attributes used for making the prediction are known as the explanatory or independent variables.
Descriptive tasks. Here, the objective is to derive patterns (correlations, trends, clusters, trajectories, and anomalies) that summarize the un- derlying relationships in data. Descriptive data mining tasks are often exploratory in nature and frequently require postprocessing techniques to validate and explain the results.
Figure 1.3 illustrates four of the core data mining tasks that are described in the remainder of this book.
Four of the core data mining tasks.
L.4
I
Figure 1.3.
8 Chapter 1 Introduction
Predictive modeling refers to the task of building a model for the target
variable as a function of the explanatory variables. There are two types of
predictive modeling tasks: classification, which is used for discrete target
variables, and regression, which is used for continuous target variables. For
example, predicting whether a Web user will make a purchase at an online
bookstore is a classification task because the target variable is binary-valued.
On the other hand, forecasting the future price of a stock is a regression task
because price is a continuous-valued attribute. The goal of both tasks is to
learn a model that minimizes the error between the predicted and true values
of the target variable. Predictive modeling can be used to identify customers
that will respond to a marketing campaign, predict disturbances in the Earth’s
ecosystem, or judge whether a patient has a particular disease based on the
results of medical tests.
Example 1.1 (Predicting the Type of a Flower). Consider the task of
predicting a species of flower based on the characteristics of the flower. In
particular, consider classifying an Iris flower as to whether it belongs to one
of the following three Iris species: Setosa, Versicolour, or Virginica. To per-
form this task, we need a data set containing the characteristics of various
flowers of these three species. A data set with this type of information is
the well-known Iris data set from the UCI Machine Learning Repository at
http: /hrurw.ics.uci.edu/-mlearn. In addition to the species of a flower,
this data set contains four other attributes: sepal width, sepal length, petal
length, and petal width. (The Iris data set and its attributes are described
further in Section 3.1.) Figure 1.4 shows a plot of petal width versus petal
length for the 150 flowers in the Iris data set. Petal width is broken into the
categories low, med’ium, and hi’gh, which correspond to the intervals [0′ 0.75),
[0.75, 1.75), [1.75, oo), respectively. Also, petal length is broken into categories
low, med,’ium, and hi,gh, which correspond to the intervals [0′ 2.5), [2.5,5), [5′ oo), respectively. Based on these categories of petal width and length, the
following rules can be derived:
Petal width low and petal length low implies Setosa. Petal width medium and petal length medium implies Versicolour. Petal width high and petal length high implies Virginica.
While these rules do not classify all the flowers, they do a good (but not
perfect) job of classifying most of the flowers. Note that flowers from the
Setosa species are well separated from the Versicolour and Virginica species
with respect to petal width and length, but the latter two species overlap
somewhat with respect to these attributes. I
r Setosa . Versicolour o Virginica
L.4 Data Mining Tasks I
l – – – – a – – f o – – – – – – – i l a o r , f t f o o t o a i : o o o I I
‘ t 0 f 0 a o 0?oo r a a r f I
? 1 . 7 5 E() r 1 . 5 E
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1 2 2 . 5 3 4 5 ( Petal Length (cm)
Figure 1.4. Petal width versus petal length for 1 50 lris flowers,
Association analysis is used to discover patterns that describe strongly as- sociated features in the data. The discovered patterns are typically represented in the form of implication rules or feature subsets. Because of the exponential size of its search space, the goal of association analysis is to extract the most interesting patterns in an efficient manner. Useful applications of association analysis include finding groups of genes that have related functionality, identi- fying Web pages that are accessed together, or understanding the relationships between different elements of Earth’s climate system.
Example 1.2 (Market Basket Analysis). The transactions shown in Ta- ble 1.1 illustrate point-of-sale data collected at the checkout counters of a grocery store. Association analysis can be applied to find items that are fre- quently bought together by customers. For example, we may discover the rule {Diapers} —–* {lt:.ft}, which suggests that customers who buy diapers also tend to buy milk. This type of rule can be used to identify potential cross-selling opportunities among related items. I
Cluster analysis seeks to find groups of closely related observations so that observations that belong to the same cluster are more similar to each other
10 Chapter 1 Introduction
Table 1 .1. Market basket data.
Tlansaction ID Items 1 2 3 4 r
o 7 8 9 10
{Bread, Butter, Diapers, Milk}
{Coffee, Sugar, Cookies, Sakoon}
{Bread, Butter, Coffee, Diapers, Milk, Eggs}
{Bread, Butter, Salmon, Chicken}
{fgg”, Bread, Butter}
{Salmon, Diapers, Milk}
{Bread, Tea, Sugar, Eggs}
{Coffee, Sugar, Chicken, Eggs}
{Bread, Diapers, Mi1k, Salt}
{Tea, Eggs, Cookies, Diapers, Milk}
than observations that belong to other clusters. Clustering has been used to
group sets of related customers, find areas of the ocean that have a significant
impact on the Earth’s climate, and compress data.
Example 1.3 (Document Clustering). The collection of news articles
shown in Table 1.2 can be grouped based on their respective topics. Each
article is represented as a set of word-frequency pairs (r, “),
where tu is a word
and c is the number of times the word appears in the article. There are two
natural clusters in the data set. The first cluster consists of the first four ar-
ticles, which correspond to news about the economy, while the second cluster
contains the last four articles, which correspond to news about health care. A
good clustering algorithm should be able to identify these two clusters based
on the similarity between words that appear in the articles.
Table 1.2. Collection of news articles.
Article Words I 2 .) A
r J
o
7 8
dollar: 1, industry: 4, country: 2, loan: 3, deal: 2, government: 2
machinery: 2, labor: 3, market: 4, industry: 2, work: 3, country: 1 job: 5, inflation: 3, rise: 2, jobless: 2, market: 3, country: 2, index: 3
domestic: 3, forecast: 2, gain: 1, market: 2, sale: 3, price: 2 patient: 4, symptom: 2, drug: 3, health: 2, clinic: 2, doctor: 2 pharmaceutical:2, company: 3, drug: 2,vaccine:1, f lu: 3
death: 2, cancer: 4, drug: 3, public: 4, health: 3, director: 2
medical: 2, cost: 3, increase: 2, patient: 2, health: 3, care: 1
1.5 Scope and Organization of the Book 11
