Clustering based text classification

Systems and methods for clustering-based text classification are described. In one aspect text is clustered as a function of labeled data to generate cluster(s). The text includes the labeled data and unlabeled data. Expanded labeled data is then generated as a function of the cluster(s). The expanded label data includes the labeled data and at least a portion of unlabeled data. Discriminative classifier(s) are then trained based on the expanded labeled data and remaining ones of the unlabeled data.

TECHNICAL FIELD

This disclosure relates to data mining, and more particularly to text clustering and text classification.

BACKGROUND

Text classification is a supervised learning task of assigning natural language text documents to one or more predefined categories or classes according to their contents. While it is a classical problem in the field of information retrieval for a half century, it is currently attracting an increased amount of attention due to an ever-expanding amount of text documents available in digital data format. Text classification is used in numerous fields including, for example, auto-processing of emails, filtering of junk emails, cataloguing Web pages and news articles, etc.

Text classification algorithms that utilize supervised learning typically require sufficient training data so that an obtained classification model can be used for sufficient generalization. As the amount of training data for each class decreases, the classification accuracy of traditional text classification algorithms dramatically degrades. In practical applications, labeled documents are often very sparse because manually labeling data is tedious and costly, while there are often abundant unlabeled documents. As a result, there is much interest in exploiting unlabeled data in text classification. The general problem of exploiting unlabeled data in supervised learning leads to a semi-supervised learning or labeled-unlabeled problem in different context.

The problem, in the context of text classification, could be formalized as follows. Each sample text document is represented by a vector x∈d. We are given two datasets Dland Du. Dataset Dlis a labeled dataset, consisting of data samples (xi, ti), where 1≦i≦n, and tiis the class label with 1≦ti≦c. Dataset Duis an unlabeled dataset, consisting of unlabeled sample data xi, n+1≦i≦n+m. The semi-supervised learning task is to construct a classifier with small generalization error on unseen data based on both Dland Du. There have been a number of work reported in developing semi-supervised text classification recently.

While it has been reported that those methods obtain considerable improvement over other supervised methods when the size of training dataset is relatively small, these techniques are substantially limited when the labeled dataset is relatively small, for instance, when it contains less than ten (10) labeled examples in each class. This is not unexpected, since these conventional techniques (e.g. co-training, TSVM and EM) typically utilize a similar iterative approach to train an initial classifier. This iterative approach is heavily based on the distribution presented in the labeled data. When the labeled data includes a very small number of samples that are distant from corresponding class centers (e.g., due to high dimensionality), these techniques will often have a poor starting point. As a result, these techniques will generally accumulate more errors during respective iterations.

In view of the above, semi-supervised learning methods construct classifiers using both labeled and unlabeled training data samples. While unlabeled data samples can help to improve the accuracy of trained models to certain extent, existing methods still face difficulties when labeled data is not sufficient and biased against the underlying data distribution.

SUMMARY

Systems and methods for clustering-based text classification are described. In one aspect text is clustered as a function of labeled data to generate cluster(s). The text includes the labeled data and unlabeled data. Expanded labeled data is then generated as a function of the cluster(s). The expanded label data includes the labeled data and at least a portion of unlabeled data. Discriminative classifier(s) are then trained based on the expanded labeled data and remaining ones of the unlabeled data.

DETAILED DESCRIPTION

Overview

The following systems and methods for clustering based text classification (CBC) utilize both labeled and unlabeled data in semi-supervised learning operations. The systems and methods first cluster training data, which includes labeled and unlabeled data, with guidance of the labeled data. At least a portion of the unlabeled data is then labeled based on the obtained clusters to generate an expanded labeled dataset. In one implementation, discriminative classifiers are then trained with the expanded labeled dataset. In this manner, the systems and methods provide for semi-supervised learning treated as clustering aided by labeled data. Such labeled data may provide important information for latent class variables, assisting in the determination of parameters associated with clustering operations to affect final clustering results. By latent class variables we mean that the variables used to generate the data samples.

For instance, if we use X to represent the latent variables and Y to represent the observed data sample, then we can describe the data dependency by the conditional probability P(Y|X). We often try as much as possible to model this probability distribution by some simplified distributions such as polynomial or Gaussian so as to simplify the parameter estimations. Additionally, in one implementation, label information is propagated to unlabeled data according to clustering results. Expanded labeled data can be used in subsequent discriminative classifiers to obtain a substantially low generalization error on unseen data. Because of these operations, CBC outperforms existing algorithms when the size of labeled dataset is very small.

CBC implements the semi-supervised learning by clustering aided by labeled data, while existing methods implement it by classification aided by unlabeled data.

As discussed above, the systems and methods for semi-supervised CBC uses both the labeled dataset Dland the unlabeled dataset Duto construct a classification model. However, how the unlabeled data could help in classification is not a trivial problem. Different methods were proposed according to different view of unlabeled data.

Expectation-Maximization (EM) has a long history in semi-supervised learning. The motivation of EM is as follows. Essentially, any classification method is to learn a conditional probability model P(t|x,θ), from a certain model family to fit the real joint distribution P(x, t). With unlabeled data, a standard statistical approach to assessing the fitness of learned models P(t|x,θ) is

∑x∈Dl⁢log⁢⁢P⁡(x|ti,θ)⁢P⁡(ti)+∑x∈Du⁢log⁢⁢∑t⁢P⁡(x|t,θ)⁢P⁡(t)(1)
where the latent labels of unlabeled data are treated as missing variables. Given Eq. 1, a Maximum Likelihood Estimation (MLE) process can be conducted to find an optimal θ. Because the form of likelihood often makes it difficult to maximize by partial derivatives, Expectation-Maximization (EM) algorithm is generally used to find a local optimal θ. Theoretically if a θ close to the global optima could be found, the result will also be optimal under the given model family. However, the selection of a plausible model family is difficult, and the local optima problem is serious especially when given a poor starting point. For example, in one approach, EM is initialized by Naive Bayes classifiers on labeled data, which may be heavily biased when there is no sufficient labeled data.

Co-Training and Transductive Support Vector Machine (TSVM) methods show sometimes superior performance over EM. For instance, a Co-Training method splits the feature set by x=(x1, x2) and trains two classifiers θ1and θ2each of which is sufficient for classification, with the assumption of compatibility, i.e. P(t|x1,θ1)=P(t|x2,θ2). Co-Training uses unlabeled data to place an additional restriction on the model parameter distribution P(θ), thus improving the estimation of real θ. The algorithm initially constructs two classifiers based on labeled data, and mutually selects several confident examples to expand the training set. This is based on the assumptions that an initial “weak predictor” could be found and the two feature sets are conditional independent. However, when labeled dataset is small, it is often heavily biased against the real data distribution. The above assumptions will be seriously violated.

TSVM adopts a totally different way of exploiting unlabeled data. TSVM maximizes margin over both the labeled data and the unlabeled data. TSVM works by finding a labeling tN+1, tn+2, . . . , tn+mof the unlabeled data Duand a hyperplane <w, b> which separates both Dland Duwith maximum margin. TSVM expects to find a low-density area of data and constructs a linear separator in this area. Although empirical results indicate the success of the method, there is a concern that the large margin hyperplane over the unlabeled data is not necessary to be the real classification hyperplane. In text classification, because of the high dimensionality and data sparseness, there are often many low-density areas between positive and negative labeled examples.

For purposes of discussion, we briefly describe concepts of high dimensionality, data sparseness, and positive and negative labeled examples. If we represent each data example as a vector (in text domain, a vector is composed of TF*IDF values for each keywords), then it can be denoted by a point in a high-dimensional space (because there are typically several hundreds of thousands of vocabularies for text document, each of which is a component of the vector). In such a high dimensional space, one data example is often far from another example. This is called the data sparseness. SVM-like classifiers treat the multi-class problem as a combination of multiple binary classification problem (in which data examples can only be labeled as either positive or negative), so it seeks to find a hyperplane to separate the two examples.

Instead of using two conditional independent features in the co-training setting, two SVM classifiers can be co-trained using two feature spaces from different views. One is the original feature space and the other is derived from clustering the labeled and unlabeled data. Two hybrid algorithms have been proposed, co-EM and self-training, using two randomly split features in co-training setting. This technique has determined that co-training is better than non-co-training algorithms such as self-training.

As a summary, existing semi-supervised methods still work in the supervised fashion, that is, they pay more attention to the labeled dataset, and rely on the distribution presented in the labeled dataset heavily. With the help of the unlabeled data, extra information on data distribution can help to improve the generalization performance. However, if the number of samples contained in the labeled data is extremely small, such existing algorithms may not work well as the labeled data can hardly represent the distribution in unseen data from the beginning. This is often the case for text classification where the dimensionality is very high and a labeled dataset of small size just represents a few isolated points in a huge space.

FIG. 1shows results of applying two algorithms to a text classification problem, wherein the number of classes is equal to 5 and the number of training samples equal 4000. The X-axis is the number of samples in each class, and the Y-axis is their performance in terms of FMicro, that as defined below. We can see that the performance of both algorithms degrades dramatically when the number of samples in each class dropped to less than a threshold number, which is this example, is 16. InFIG. 1, we depict another line, the dotted line, to indicate the performance using a clustering method, K-means, to cluster the same set of training data. In the experiments, we ignore the labels; hence in contrast to the algorithms used to generate data for the other two lines, the dotted line represents performance of unsupervised learning. It is interesting to see that when the number of labeled data in each class is less than 4, unsupervised learning in fact gives better performance than both semi-supervised learning algorithms. Results such as this indicate that a clustering based approach to the problem of semi-supervised learning would be useful.

Clustering Based Classification

FIG. 2illustrates an exemplary system200for clustering based text classification. System200includes computing device202, including program module(s)204and program data206. Program modules include, for example, cluster based text classification (CBC) module208for clustering training dataset210. Exemplary data sets210, may comprise data relating to any activity or subject matter. In one implementation, the data set210included material from commonly used datasets such as 20-Newsgroups, Reuters-21578, and Open Directory Project (ODP) web pages. CBC module208clusters unlabeled data212with the guidance of labelled data214to generate clusters216. CBC module208expands the labeled data214according to the clustering result. To this end, CBC module208determines that at least a portion of the unlabeled data212can be viewed as labeled dataset214with high confidence. It is this portion that represents expanded label dataset218. Criteria for determining when unlabeled data can be used as labeled data for the expanded label dataset218are described below.

The expanded labeled dataset218is used to construct the final classification model. CBC module208trains classifiers220with the label data214, which now includes expanded labeled dataset218and the remaining unlabeled data212(i.e., the unlabeled data minus the unlabeled data that is not being treated as part of the expanded label dataset218).

FIG. 3shows exemplary results of a conventional clustering approach with original labeled data. The black points and grey points in the Figure represent data samples of two different classes. We have very small number of labeled data, e.g. one for each class, represented by the points with “+” and “−” signs. A classification algorithm trained with these two points will most likely find line “A” as shown in as the class boundary; and it's also rather difficult to discover the real boundary B even with the help of the unlabeled data points. Firstly, this is because the initial labeled samples are highly biased, they will cause poor starting points for iterative reinforcement algorithms such as Co-Training and EM. Moreover, TSVM algorithm may also result in line A because it happens to lie in a low density area. In fact in a feature space with high dimensionality, a single sample is often highly biased; and many low density areas will exist.

FIGS. 4 and 5show exemplary results of the systems and methods for clustering based text classification. For purposes of discussion, aspects ofFIGS. 2 and 3are discussed with respect to the features ofFIG. 2. The left-most digit of a component reference number identifies the particular Figure in which the component first appears. As described above, CBC module208applies a clustering algorithm to training dataset210. In these examples, these clustering operations result in two clusters. The black and gray data points are unlabeled examples. The big “+” and “−” are two initially labeled example, and small “+” and “−” are examples expanded by clustering. CBC module208propagates the labels of the labeled data samples214to the unlabeled samples212which are closest to cluster centroids to generate expanded label dataset218. As a result, we have more labeled data samples214, as shown inFIG. 4. CBC module208uses the expanded labeled data214and remaining unlabeled data212to train a classifier220. As the result, CBC module208identifies a substantially better class boundary, as shown inFIG. 5.

This approach combines merits of both clustering and classification methods. Clustering operations reduce the impact of any bias caused by initial sparse labeled data. With sufficient expanded labeled data, the CBC module208uses discriminative classifiers to achieve better generalization performance than pure clustering methods. More particularly, clustering methods are more robust to the bias caused by the initial sparse labeled data. Let us take k-means, the most popular clustering algorithm as an example. In essence, k-means is a simplified version of EM working on spherical Gaussian distribution models. They can be approximately described by MLE of k spherical Gaussian distributions, where the means μ1, . . . , μkand the identical covariances Σ are latent variables. Thus with the aid of labeled data, the objective is to find an optimal θ=<μ1, . . . , μk, Σ> to maximize the log-likelihood of Eq. 1 where the P(x|ti, θ) equals to

1(2⁢π)d/2·Σ1/2·exp⁡(-12⁢(x-μi)T⁢⁢Σ-1⁡(x-μi))(2)
When the number of labeled examples is small, the bias of labeled example will not affect much the likelihood estimation and the finding of the optimal θ.

Second, methodology of CBC module208represents a generative classifier, i.e., it constructs a classifier derived from the generative model of its data P(x|t,θ). The generative classifier and discriminative classifier (such as logistic regression, which is a general form of SVM) has been theoretically and empirically analyzed with respect to asymptotic performance. This analysis shows that generative classifiers reach their asymptotic performance faster than discriminative classifiers. For at least these reasons, CBC module208clustering operations are more effective with small training data, and make it easier to achieve high performance when labeled data is sparse. To address the problem that generative classifiers usually lead to higher asymptotic error than discriminative classifiers, discriminative classification method such as TSVM can be used in the second step of our approach, i.e., after clustering unlabeled data and expanding the labeled data set.

CBC module208clustering is guided by labeled data. Generally, clustering methods address the issue of finding a partition of available data which maximizes a certain criterion, e.g. intra-cluster similarity and inter-cluster dissimilarity. The labeled data is used to modify the criterion. There are also some parameters associated with each clustering algorithm, e.g. the number k in k-means, or split strategy of dendrogram in hierarchical clustering. The labeled data can also be used to guide the selection of these parameters. In this implementation, CBC module208uses a soft-constraint version of k-means algorithm for clustering, where k is equal to the number of classes in the given labeled data set. The labeled data points are used to obtain the initial labeled centroids, which are used in the clustering process to constraint the cluster result.

Combining Clustering with Classification

Two-step clustering based classification, i.e., clustering followed by classification, can be viewed as a conceptual approach. Another strategy of combining clustering and classification is through iterative reinforcement. That is, we first train a clustering model L1based on all available data, obtaining an approximately correct classifier. Afterwards, we select from unlabeled data examples that are confidently classified by L1(i.e. examples with high likelihood) and combine them with original labeled data to train a new model L2. Because more labeled data are used, the obtained L2is expected to be more accurate and can provide more confident training examples for L1. We use the new labeled dataset to train L1again. This process is iterated until all examples are labeled.

We now describe how the labeled dataset214is expanded. In principle, we can just assign the label to the most confident p % of examples from each of the resulting clusters. If we choose p=100% after first clustering process, we actually have a two-step approach. First, we determine the value of p. The selection of p is a tradeoff between the number of labeled samples and possible noise introduced by the labeling error. Obviously, with higher p, a large labeled dataset will be obtained. In general, a classifier with higher accuracy can be obtained with more training samples. On the other hand, when we expand more samples, we might introduce incorrectly labeled samples into the labeled dataset, which become noise and will degrade the performance of a classification algorithm. Furthermore, small p means more iteration in the reinforcement process.

We choose “confident examples” of unlabeled data212for expanding the labeled dataset214. Note that any learned model is an estimation of the real data model P(x,t). We can find examples that are confidently classified by a given model if a slightly change of θ has no impact on them. When more examples are given, the model estimation will become more accurate, and the number of confident examples will grow. As illustrated inFIGS. 4 and 5, even when some of the data points are wrongly classified, the most confident data points, i.e. the ones with largest margin under classification model and the ones nearest to the centroid under clustering model, are confidently classified. That is, a slightly change of the decision boundary or centroid will not affect the label of these data.

We assume that class labels t are uniformly distributed. Since the Gaussian is spherical, the log-likelihood of a given data point and the estimated label is
log(P(x*,t*|θ))=log(P(x*|t*,θ)P(t*|θ)=−c1∥x−μ*∥2+c2(3)
where c1and c2are positive constants. The most probable points in a single Gaussian distribution are the points that are nearest to the distribution mean.

To get the most confident examples from the result of TSVM, we draw a probabilistic view of the TSVM. Let us take logistic regression as an example, which is a general form of discriminative methods. The objective is to maximize

∑i⁢log⁢11+ⅇ-yi⁢f⁡(xi,θ)(4)
where f(xi,θ) is some linear function depending on the parameter θ. θ is typically a linear combination of training examples. Under the margin maximization classifier such as SVM, the likelihood of a given point x* and its label t*=+ can be derived from the above equation:

P⁡(x*,+)=P⁡(x)⁢(1-11+exp(∑j⁢tj(∑k⁢βjk)⁢(xj·x)+b))(5)
which considers points with largest margin the most probable.
An Exemplary Procedure

FIG. 6shows an exemplary procedure600for clustering based text classification of system200ofFIG. 2. For purposes of discussion, aspects of procedure600are discussed with respect to the features ofFIG. 2. The left-most digit of a component reference number identifies the particular Figure in which the component first appears. In this implementation, the detailed algorithm of CBC module208, is applied to text data (training dataset210), which is generally represented by sparse term vectors in a high dimensional space.

At block602, CBC module208tokenizes all documents of data set210into terms and constructs one component for each distinct term. Such tokenized information and resulting vectors are shown by respective portions of “other data”222ofFIG. 2. Thus each document is represented by a vector (wi1, wi2, . . . , wid) where wijis weighted by TFIDF, i.e. wij=TFij×log(N/DFj), where N s total number of documents. The term vectors are normalized.

At block604, CBC module208clusters the tokenized terms with the help of labeled data214to generate cluster(s)216. In this implementation, CBC module208implements an iterative reinforcement strategy. During each iteration, a soft-constrained version of k-means is used for clustering. We compute the centroids of the labeled data for each class (which is called “labeled centroids”) and use them as the initial centroids for k-means. (Such computed centroids are shown as a respective portion of “other data”222). The k value is set to the number of classes in the labeled data214. CBC module208runs k-means on both labeled214and unlabeled data212. The iterative loop is terminated when clustering result doesn't change anymore, or just before a labeled centroid being assigned to a wrong cluster. This sets “soft constraints” on clustering because the constraints are not based on exact examples but on their centroid. The constraints will reduce bias in the labeled examples. Finally, at least a portion of unlabeled data212are assigned labels as labeled centroid in the same cluster.

Exemplary operations of block604are described in greater detail, wherein input includes: labeled data set Dl, unlabeled data set Du, the full labeled set Dl′=Dl+(Du, Tu*). The current labeled and unlabeled data sets are initialized as Dl′=Dl, Du′=Du. These clustering operations are repeated until Du′=Ø (cluster result doesn't change any more).1. Calculate initial centroids

oi*=∑∀j,tj=i⁢⁢xj,
i=1 . . . c, xj∈Dl+Du.3. From each cluster, select p % examples xi∈Du′ which is nearest to oi*, and add them to Dl′.

In this implementation, a cosine function is used as a similarity measure for two documents:

sim⁡(docj,dock)=∑i=1d⁢⁢wij·wik.
This measure is also used in the clustering algorithm to calculate the distance from an example to a centroid (which is also normalized). This simple representation is efficient for supervised learning, e.g. in most tasks they are linear separatable.

At block606, CBC module208selects substantially most confident examples (i.e. examples nearest to cluster centroids) to form a new labeled set214, which includes expanded label dataset218, together with remaining unlabeled data212, to train a TSVM classifier220.

At block608, CBC module208trains discriminative classifier(s)220based on Dl′ and Du′. In this implementation, CBC module208uses a TSVM classifier with a linear kernel. At block610, it is determined whether all examples have class labels. If so, then the classifier(s)220are ready to be used to classify text. At block612, text is classified using the classifier(s)220. For purposes of illustration, text to be classified and classified text is shown as a respective portion of “other data”122ofFIG. 1. If there are still unlabeled examples, clustering module604continues at block614, to cluster vectors with the help of the new labeled data. To this end, from each resulting cluster or class (see “other data”122ofFIG. 2), clustering module604or classification module608selects p % confident examples xi∈Du′ (i.e., examples with minimum distance to cluster centroids or examples with substantially maximum classification confidence), and adds them to Dl′. At this point, the procedure continues at block604as described above.

An Exemplary Operating Environment

Although not required, the systems and methods for clustering based text classification are described in the general context of computer-executable instructions (program modules) being executed by a personal computer. Program modules generally include routines, programs, objects, components, data structures, etc., that perform particular tasks or implement particular abstract data types. While the systems and methods are described in the foregoing context, acts and operations described hereinafter may also be implemented in hardware.

FIG. 7illustrates an example of a suitable computing environment for clustering based text classification may be fully or partially implemented. Exemplary computing environment700is only one example of a suitable computing environment and is not intended to suggest any limitation as to the scope of use or functionality of systems and methods the described herein. Neither should computing environment700be interpreted as having any dependency or requirement relating to any one or combination of components illustrated in computing environment700.

The methods and systems described herein are operational with numerous other general purpose or special purpose computing system, environments or configurations. Examples of well-known computing systems, environments, and/or configurations that may be suitable for use include, but are not limited to, personal computers, server computers, multiprocessor systems, microprocessor-based systems, network PCs, minicomputers, mainframe computers, distributed computing environments that include any of the above systems or devices, and so on. Compact or subset versions of the framework may also be implemented in clients of limited resources, such as handheld computers, or other computing devices. The invention is practiced in a distributed computing environment where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules may be located in both local and remote memory storage devices.

With reference toFIG. 7, an exemplary system for clustering based text classification includes a general purpose computing device in the form of a computer710implementing, for example, system200ofFIG. 2. The following described aspects of computer710are exemplary implementations of client computing device202ofFIG. 2. Components of computer710may include, but are not limited to, processing unit(s)720, a system memory730, and a system bus721that couples various system components including the system memory to the processing unit720. The system bus721may be any of several types of bus structures including a memory bus or memory controller, a peripheral bus, and a local bus using any of a variety of bus architectures. By way of example and not limitation, such architectures may include Industry Standard Architecture (ISA) bus, Micro Channel Architecture (MCA) bus, Enhanced ISA (EISA) bus, Video Electronics Standards Association (VESA) local bus, and Peripheral Component Interconnect (PCI) bus also known as Mezzanine bus.

System memory730includes computer storage media in the form of volatile and/or nonvolatile memory such as read only memory (ROM)731and random access memory (RAM)732. A basic input/output system733(BIOS), containing the basic routines that help to transfer information between elements within computer710, such as during start-up, is typically stored in ROM731. RAM732typically contains data and/or program modules that are immediately accessible to and/or presently being operated on by processing unit720. By way of example and not limitation,FIG. 7illustrates operating system734, application programs735, other program modules736, and program data738.

The computer710may also include other removable/non-removable, volatile/nonvolatile computer storage media. By way of example only,FIG. 7illustrates a hard disk drive741that reads from or writes to non-removable, nonvolatile magnetic media, a magnetic disk drive751that reads from or writes to a removable, nonvolatile magnetic disk752, and an optical disk drive755that reads from or writes to a removable, nonvolatile optical disk756such as a CD ROM or other optical media. Other removable/non-removable, volatile/nonvolatile computer storage media that can be used in the exemplary operating environment include, but are not limited to, magnetic tape cassettes, flash memory cards, digital versatile disks, digital video tape, solid state RAM, solid state ROM, and the like. The hard disk drive741is typically connected to the system bus721through a non-removable memory interface such as interface740, and magnetic disk drive751and optical disk drive755are typically connected to the system bus721by a removable memory interface, such as interface750.

The drives and their associated computer storage media discussed above and illustrated inFIG. 7, provide storage of computer-readable instructions, data structures, program modules and other data for the computer710. InFIG. 7, for example, hard disk drive741is illustrated as storing operating system744, application programs745, other program modules746, and program data748. Note that these components can either be the same as or different from operating system734, application programs735, other program modules736, and program data738. Application programs735includes, for example CBC module208ofFIG. 2. Program data738includes, for example, training data set210, cluster(s)216, classifier(s)220, and other data222. Operating system744, application programs745, other program modules746, and program data748are given different numbers here to illustrate that they are at least different copies.

A user may enter commands and information into the computer710through input devices such as a keyboard762and pointing device761, commonly referred to as a mouse, trackball or touch pad. Other input devices (not shown) may include a microphone, joystick, game pad, satellite dish, scanner, or the like. These and other input devices are often connected to the processing unit720through a user input interface760that is coupled to the system bus721, but may be connected by other interface and bus structures, such as a parallel port, game port or a universal serial bus (USB).

A monitor791or other type of display device is also connected to the system bus721via an interface, such as a video interface790. In addition to the monitor, computers may also include other peripheral output devices such as speakers798and printer796, which may be connected through an output peripheral interface795.

The computer710operates in a networked environment using logical connections to one or more remote computers, such as a remote computer780. The remote computer780may be a personal computer, a server, a router, a network PC, a peer device or other common network node, and as a function of its particular implementation, may include many or all of the elements described above relative to the computer710, although only a memory storage device781has been illustrated inFIG. 7. The logical connections depicted inFIG. 7include a local area network (LAN)781and a wide area network (WAN)783, but may also include other networks. Such networking environments are commonplace in offices, enterprise-wide computer networks, intranets and the Internet.

When used in a LAN networking environment, the computer710is connected to the LAN781through a network interface or adapter780. When used in a WAN networking environment, the computer710typically includes a modem782or other means for establishing communications over the WAN783, such as the Internet. The modem782, which may be internal or external, may be connected to the system bus721via the user input interface760, or other appropriate mechanism. In a networked environment, program modules depicted relative to the computer710, or portions thereof, may be stored in the remote memory storage device. By way of example and not limitation,FIG. 7illustrates remote application programs785as residing on memory device781. The network connections shown are exemplary and other means of establishing a communications link between the computers may be used.

CONCLUSION

Although the systems and methods for clustering based text classification have been described in language specific to structural features and/or methodological operations or actions, it is understood that the implementations defined in the appended claims are not necessarily limited to the specific features or actions described. For instance, in one implementation, other clustering methods can be used and/or adjustments of the similarity measure with the aid of labeled examples. In yet another implementation, validity of two general classifiers is evaluated in the described CBC framework of system200, confidence assessment, and noise control is also considered for additional performance improvements. Accordingly, the specific features and actions are disclosed as exemplary forms of implementing the claimed subject matter.