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780 Mohamed Medhat Gaber, Arkady Zaslavsky, and Shonali Krishnaswamy
constrained device that generates or receive streams of information. AOG has three
main stages. Mining followed by adaptation to resources and data stream rates repre-
sent the first two stages. Merging the generated knowledge structures when running
out of memory represents the last stage. AOG has been used in clustering, classifica-
tion and frequency counting (Gaber et al., 2005).
Figure 39.8 shows a flowchart of AOG-mining process. It shows the sequence of
the three stages of AOG.
Fig. 39.8. AOG Approach
Definitions, advantages and disadvantages of all of the above task-based ap-
proaches are given in Table 39.3.
39.8 Related Work
The last few years have witnessed the emergence of data management strategies
focusing on data stream issues (Babcock et al., 2002). Querying and summarizing
data that could be stored for further analysis are the main processing tasks studied
in data stream management systems. Extension of query languages, query planning,
scheduling, and optimization are the major research activities conducted in this area.
Aurora (Abadi et al., 2003), COUGAR (Yao and Gehrke, 2002), Gigascope (Cra-
nor et al., 2003), STREAM (Arasu et al., 2003), TelegraphCQ (Krishnamurthy et
al., 2003) represent the first generation of data stream management systems. In this
section, a brief description of each one is given as follows:
• STREAM: STanford stREam datA Manager (STREAM) (Arasu et al., 2003) is a
data stream management system that handles multiple continuous data streams
and supports long-running continuous queries. The intermediate results of a con-
tinuous query are stored in a data structure termed Scratch Store. The results of a
query could be a data stream transferred to the user or it could be a relation that
also could be stored for re-processing. To support continuous queries over data
streams, a continuous query language termed as CQL has been developed as part
of the system. The language supports relation-to-relation, stream-to-relation, and
relation-to-stream operators.
• Gigascope: is a specialized data stream management system (Cranor et al., 2003)


for the application of network monitoring. It has its own SQL-like query language
termed as GSQL. Unlike CQL, the input and output of this language are only
39 Data Stream Mining 781
Table 39.3. Task-based Techniques
Technique Definition Pros Cons
Approximation Al-
gorithms
Design algorithms
that approximate
mining results with
error bounds.
• Efficiency in
running time.
• the problem
of data rates
with regard
to the avail-
able resources
could not be
solved using
approximation
algorithms.
Sliding Window Analyzing the most
recent data streams
• Applicable
to most of
data stream
applications.
• don’t provide
a model for

the whole data
stream.
Algorithm Output
Granularity
Adapting the
algorithm param-
eters according
to data stream
rate and memory
consumption
• Generic ap-
proach that
could be
used with
any mining
technique with
no or minor
modifications
• It has an over-
head when run-
ning for long
period of time
data streams. GSQL supports merge, selection, join and aggregation operations
on data streams. Query optimization and performance considerations have been
addressed in developing the language. The system serves a number of network
related applications including intrusion detection and traffic analysis.
• TelegraphCQ: is a continuous query processing system (Krishnamurthy et al.,
2003) built on the basis of PostgreSQL open source query language. The system
supports creating data streams, sources, wrappers and queries.
• COUGAR: is a data stream management system (Yao and Gehrke, 2002) de-

signed for sensor networks. Motivated by the fact that local computation in sen-
sor networks is cheaper than transferring data generated from sensors over wire-
less connections, a loosely coupled distributed architecture has been proposed to
answer in-network queries.
• Aurora: is a data stream management system (Abadi et al., 2003) that has the
optimization features for load shedding, real-time query scheduling and QoS as-
sessment. It is mainly designed to deal with very large numbers of data streams.
782 Mohamed Medhat Gaber, Arkady Zaslavsky, and Shonali Krishnaswamy
Queries over data streams have some similarities with data stream mining in
terms of research issues and challenges. The two main constraints for querying
data streams are the unbounded memory requirement and the high data rate. Thus,
the computation time per data element/record should be less than the data rate or
the sampling rate. Furthermore, the unbounded memory requirement compounds
the challenge by necessitating approximate rather than exact results. Significant re-
search efforts have been conducted to approximate the query results (Babcock et al.,
2002, Garofalakis et al., 2002b).
The data stream mining algorithms have used some of the techniques introduced
in the data stream management research. Sampling and load shedding (Muthukrish-
nan, 2003) are among the basic techniques that have been introduced in querying
data streams and extended to the data mining process.
39.9 Future Directions
The field of data stream mining is in a nascent stage of evolution. The last few years
have witnessed increased attention to this area of research due to the dissemination
of data stream sources. Based on the state-of-the-art in the area and demands of data
streaming applications, we can identify the future directions of research as follows:
• Developing data mining algorithms for wireless sensor networks to serve a num-
ber of real-time critical applications.
• Online medical, scientific and biological data stream mining using data generated
from medical, biological instruments and various tools employed in scientific
laboratories.

• Hardware solutions to small devices emitting or receiving data streams in order
to enable high performance computation on small devices.
• Developing software architectures that serve data streaming applications.
39.10 Summary
In this chapter, a review of the state of the art in mining data streams has been pre-
sented. Clustering, classification, frequency counting, time series analysis techniques
have been discussed. Different systems that use data stream mining techniques have
been also presented. Generalization of the approaches used in developing data stream
mining techniques is given. The approaches have been broadly classified into data-
based and task-based strategies. Sampling, load shedding, sketching, synopsis data
structure creation and aggregation represent the data-based approaches. Approxi-
mation algorithms, sliding window and algorithm output granularity are the two ap-
proaches that form the task-based approaches. The chapter is concluded with pointers
to future research directions in the area.
39 Data Stream Mining 783
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40
Mining Concept-Drifting Data Streams
Haixun Wang
1
, Philip S. Yu
2
, and Jiawei Han
3
1
IBM T. J. Watson Research Center


2
IBM T. J. Watson Research Center

3
University of Illinois, Urbana Champaign

Summary. Knowledge discovery from infinite data streams is an important and difficult task.
We are facing two challenges, the overwhelming volume and the concept drifts of the stream-
ing data. In this chapter, we introduce a general framework for mining concept-drifting data
streams using weighted ensemble classifiers. We train an ensemble of classification models,
such as C4.5, RIPPER, naive Bayesian, etc., from sequential chunks of the data stream. The
classifiers in the ensemble are judiciously weighted based on their expected classification ac-
curacy on the test data under the time-evolving environment. Thus, the ensemble approach
improves both the efficiency in learning the model and the accuracy in performing classifica-
tion. Our empirical study shows that the proposed methods have substantial advantage over
single-classifier approaches in prediction accuracy, and the ensemble framework is effective
for a variety of classification models.
Key words: Data Mining, concept learning, classifier design and evaluation
40.1 Introduction
Knowledge discovery on streaming data is a research topic of growing interest (Bab-
cock et al., 2002, Chen et al., 2002, Domingos and Hulten, 2000, Hulten et al.,
2001). The fundamental problem we need to solve is the following: given an infi-
nite amount of continuous measurements, how do we model them in order to capture
time-evolving trends and patterns in the stream, and make time-critical predictions?
Huge data volume and drifting concepts are not unfamiliar to the Data Min-
ing community. One of the goals of traditional Data Mining algorithms is to
learn models from large databases with bounded-memory. It has been achieved
by several classification methods, including Sprint (Shafer et al., 1996), BOAT
(Gehrke et al., 1999), etc. Nevertheless, the fact that these algorithms require multi-

ple scans of the training data makes them inappropriate in the streaming environment
where examples are coming in at a higher rate than they can be repeatedly analyzed.
O. Maimon, L. Rokach (eds.), Data Mining and Knowledge Discovery Handbook, 2nd ed.,
DOI 10.1007/978-0-387-09823-4_40, © Springer Science+Business Media, LLC 2010

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