Contents
What is a collective anomaly?
Collective Anomalies. If a collection of related data instances is anomalous with respect to the entire data set, it is termed as a collective anomaly. The individual data instances in a collective anomaly may not be anomalies by themselves, but their occurrence together as a collection is anomalous.
What is time series data anomalies?
In time series data, an anomaly or outlier can be termed as a data point which is not following the common collective trend or seasonal or cyclic pattern of the entire data and is significantly distinct from rest of the data.
What is a point anomaly?
If a single instance in a given dataset is different from others with respect to its attributes, it is called a point anomaly. If the data is anomalous in some context, it is called contextual anomaly. In the absence of a context, all the data points look normal.
How do you detect collective anomaly?
Olsson et al. [15] proposed an unsupervised approach for detecting collective anomaly. In order to detect a group of the anomalous examples, the “anomalous score” of the group of data points was probabilistically aggregated from the contribution of each individual examples.
What’s the difference between a point anomaly and a collective anomaly?
In contrast, occurrence of contextual anomalies depends on the availability of context attributes in the data. A point anomaly or a collective anomaly can also be a contextual anomaly if analyzed with respect to a context.
When do point anomalies occur in a data set?
It should be noted that while point anomalies can occur in any data set, collective anomalies can occur only in data sets in which data instances are related. In contrast, occurrence of contextual anomalies depends on the availability of context attributes in the data.
Which is a use case for collective anomalies?
Collective anomalies: A set of data instances collectively helps in detecting anomalies. Business use case: Someone is trying to copy data form a remote machine to a local host unexpectedly, an anomaly that would be flagged as a potential cyber attack.
What is the definition of contextual and collective anomalies?
Contextual and collective anomalies are defined as follows ( source ): Contextual Anomalies. If a data instance is anomalous in a specific context (but not otherwise), then it is termed as a contextual anomaly (also referred to as conditional anomaly Collective Anomalies.