A Temporal Self-Organizing Neural Network for
Adaptive Sub-sequence Clustering and Case Studies
Dong Wang
∗
, Yanfang Long
∗
, Zhu Xiao
∗
, Zhiyang Xiang
∗
and Wenjie Chen
†
∗
Colledge of Computer Science and Electronics Engineering,
Hunan University, Changsha, China
Email: {wangd,hndx
lyf,zhxiao,z xiang}@hnu.edu.cn
†
Business college, Central South University of Forestry and Technology
Email: wendychen711@126.com
Abstract—Temporal neural networks such as Temporal Koho-
nen Map (TKM) and Recurrent Self-Organizing Map (RSOM)
are popular for their incremental and explicit learning abilities.
However, for sub-sequence clustering TKM and RSOM may
generate many fragments whose classification membership is
hard to decide. Besides they have stability issues in multivari-
ate time series processing because they model the historical
neuron activities on each variable independently. To overcome
the drawbacks, we propose an adaptive sub-sequence clustering
method based on single layered Self-Organizing Incremental
Neural Network (SOINN). A recurrent filter is proposed to model
the quantizations of neuron activations each as a scalar instead
of a vector like in TKM and RSOM. Then it is integrated
with the single layered SOINN for adaptive clustering where
fragmented clusters in TKM and RSOM is replaced by a
smoothed clustering result. Experiments are carried out on
two datasets, namely a traffic flow dataset from open Caltrans
performance measurement systems and a part of the KDD Cup
99 intrusion detection dataset. Experimental results show that
the proposed method outperforms the conventional methods by
21.3% and 9.1% on the two datasets respectively.
Index Terms—Recurrent neural network, sub-sequence clus-
tering, adaptive clustering, self-organizing incremental neural
network
I. INTRODUCTION
Sub-sequence clustering algorithms are effective time series
data analysis techniques. Applications such as atmosphere
engineering [1], traffic flow predictions [2] depends heavily
on time series sub-sequence analysis techniques. Visualization
of time series data enables visual analysis which is a unique
way to combine expert experiences and automated knowledge
discovery. Moreover, time series clustering is related to an
important set of problems in data mining, namely the data
stream mining. Time domain mining is crucial for concept
drift detection in data stream environments. However, despite
the large amount of research on spatial clustering, time series
clusterings are given far less attention.
Through clustering a generalization of the data is obtained,
usually in the form of clustering centers. More detailed anal-
ysis involves classification of the clustering centers. Unfor-
tunately, the classification of clustering centers are proved
expensive and time consuming even they are much smaller
in number than the original data. Adaptive clustering is an
effort that can minimize the number of clustering centers that
require expert knowledge to classify.
Adaptive clustering methods work under assumptions of the
data distribution, which is similar to semi-supervised learning
(SSL) [3]. In terms of SSL, data are said to be distributed
under the smooth assumption if the samples that are similar to
each other are more likely to be classified the same. Adaptive
learning based on self-organizing incremental neural network
(SOINN) [4] propagates labels from clustering centers to
similar ones so that only one of the neurons labeled the same
needs expert inspections. Hierarchical methods for adaptive
clustering such as [5], are in fact assuming clustering centers
distributing under the smooth assumption and low density
assumption. In the low density assumption data separated by
low density areas are considered belonging to different models.
Segmentation methods that split time series data into seg-
ments each with its own properties are closely related to time
series sub-sequence clustering. The sliding window solution is
widely used to transform time series patterns into a geometric
space, then the clustering tasks are carried out by conventional
clustering methods [6]. The learning is implicit and is different
from recurrent neural network’s explicit learning. In time
series analysis, the drawback of sliding window technique is
that the dimensionality of transformed data is increased. Such
dimension increase compromises both the performance and
efficiency of the conventional clustering methods.
Temporal Self-Organizing Map (SOM) including Tempo-
ral Kohonen Map (TKM) [7], Recurrent SOM (RSOM) [8]
and Recursive SOM [9] are time series clustering methods
without sliding window model. In TSOM a recurrent filter
is introduced to synthesize an input with the current sample
and its relationship with historical samples. RSOM always
functions as a solution of nonlinear prediction of time series
[8], [10]. Nevertheless, for sub-sequence clustering it produces
fragments too many and their inter similarity is difficult to
measure. In other words, RSOM is ineffective in terms of
adaptive sub-sequence clustering. Except for sub-sequence
clustering, RSOM is the most widely used method for time se-
ries visualization [10]. Recursive growing neural gas (RGNG)
learns the topology in a self-organized manner so that the
limitation of a pre-defined neighborhood function is RSOM
is remedied. However, RGNG inherits the endless growing of
neurons drawback of growing neural gas.
In this paper we propose a neural network approach for
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