Data mining. Textbook. Vadim Shmal

and the frequency of deviation. It can also provide a link to the main rejection process. This information can be used to understand the root cause of the deviation. A higher data rejection rate provides valuable insight into the rejection process. In such a situation, the risk of deviation is likely to be detected and necessary process changes can be assessed.

      Many studies are conducted on the analysis of data anomalies to identify factors that contribute to the occurrence of data anomalies. Some of these factors relate to processes that require frequent process changes. Some of these factors can be used to identify processes that may be abnormal. Many parameters can be found in systems providing process performance.

      Association Rule Learning

      Association rule learning is a rule-based machine learning technique for discovering interesting relationships between variables in large sample databases. This technique is inspired by the auditory system, where we learn the association rules of an auditory stimulus and that stimulus alone.

      Sometimes when working with a dataset, we are not sure if the rows in the dataset are relevant to the training task, and if so, which ones. We may want to skip those rows in the dataset that don’t matter. Therefore, associations are usually determined by non-intuitive criteria, such as the order in which these variables appear in a sequence of examples, or duplicate values in these data rows.

      This problematic aspect of learning association rules can be eliminated in the form of an anomaly detection algorithm. These algorithms attempt to detect non-standard patterns in large datasets that may represent unusual relationships between data features. These anomalies are often detected by pattern recognition algorithms, which are also part of statistical inference algorithms. For example, the study of naive Bayes rules can detect anomalies in the study of association rules based on a visual inspection of the presented examples.

      In a large dataset, a feature space can represent an area of an image as a set of numbers, in which each image pixel has a certain number of pixels. The characteristics of an image can be represented as a vector, and we can place this vector in the feature space. If the attribute space is not empty, the attribute will be the number of pixels in the image that belong to a particular color.

      Clustering

      Clustering is the task of discovering groups and structures in data that are «similar» to some extent, not by using known structures in the data, but by learning from what is already there.

      In particular, clustering is used in such a way that new data points are only added to existing clusters, without changing their shape to fit the new data. In other words, clusters are formed before data is collected, rather than fixed after all data is collected.

      Given a set of parameters for data that is (mostly) variable, and their «collinearity», clustering can be thought of as a hierarchical algorithm for finding clusters of data points that satisfy a set of criteria. Parameters can be grouped into one of two categories: parameter values that define the spatial arrangement of clusters, and parameter values that define relationships between clusters.

      Given a set of parameters for a dataset, clustering can be thought of as discovering those clusters. What parameters do we use for this? The implicit clustering method, which finds the nearest clusters (or, in some versions, clusters more similar to each other) with the least computational cost, is probably the simplest and most commonly used method for doing this. In clustering, we aim to keep the clusters as closely related to each other as possible – whether we do this by taking more measurements or by using only a certain technique to collect data.

      But what is the difference between clustering and splitting data into one or more datasets?

      The methods of implicit clustering and managed clustering are actually very similar. The only difference is that we use different parameters to determine in which direction we should split the data. Take as an example a set of points on a sphere that define an interconnected network. Both methods aim to keep the network as close as possible to the network defined by the two nearest points. This is because we don’t care if we are very far from one or the other. So, using the implicit clustering algorithm (cluster distance), we will divide the sphere into two parts that define very different networks: one will be the network defined by the two closest points, and the other will be the network defined by the two farthest points. The result is two completely separate networks. But this is not a good approach, because the further we move away from the two closest points, the smaller the distance between the points, the more difficult it will be to find connections between them – since there is a limited number of points that are connected by a small distance.

      On the other hand, the method of controlled clustering (cluster distance) would require us to measure the length between each pair of points, and then perform calculations that make the networks closest to each other the smallest distance possible. The result is likely to be two separate networks that are close to each other but not exactly the same. Since we need two networks to be similar to each other in order to detect a relationship, it is likely that this method will not work – instead, the two clusters will be completely different.

      The difference between these two methods comes down to how we define a «cluster». The point is that in the first method (cluster distance) we define a cluster as a set of points belonging to a network similar to a network defined by two nearest points. By this definition, networks will always be connected (they will be the same distance apart) no matter how many points we include in the definition. But in the second method (clustering control), we define clusters as pairs of points that are the same distance from all other points in the network. This definition can make finding connected points very difficult because it requires us to find every point that is similar to other points in the network. However, this is an understandable compromise. By focusing on finding clusters with the same distance from each other, we are likely to get more useful data, because if we find connections between them, we can use this information to find the relationship between them. This means that we have more opportunities to find connections, which will make it easier to identify relationships. By defining clusters using distance measurements, we ensure that we can find a relationship between two points, even if there is no way to directly measure the distance between them. But this often results in very few connections in the data.

      Looking at the example of creating two datasets – one for implicit clustering and one for managed clustering – we can easily see the difference between the two methods. In the first example, the results may be the same in one case and different in another. But if the method is good for finding interesting relationships (as it usually is), it will give us useful information about the overall structure of the data. However, if the technique is not good at identifying relationships, then it will give us very little information.

      Let’s say we are developing a system for determining the direction of a new product and want to identify similar products. Since it is not possible to measure the direction of a product outside the system, we will have to find relationships between products based on information about their names. If there is a good rule that we can use to establish relationships between similar products, then this information is very useful as it allows us to find interesting relationships (by identifying similar products that appear close to each other). However, if the relationship between two products isn’t very obvious, it’s likely that it’s just an unrelated relationship – which means the feature detection method we choose may not matter much. On the other hand, if the relationship is not very obvious but extremely useful (as in the example above), then we can start to learn how the product name is related to the process the product went through. This is an example of how different methods can produce very different results.

      Unlike the characteristics of different methods, you also have different possible techniques. For example, when I say that my system uses image recognition, it doesn’t necessarily mean that the process the product goes through uses image recognition. If there are product images that we have taken in the past, or if we have captured