  An edge stream is a common form of presentation of dynamic networks. It can
evolve with time, with new types of nodes or edges being continuously added.
Existing methods for anomaly detection rely on edge occurrence counts or
compare pattern snippets found in historical records. In this work, we propose
Isconna, which focuses on both the frequency and the pattern of edge records.
The burst detection component targets anomalies between individual timestamps,
while the pattern detection component highlights anomalies across segments of
timestamps. These two components together produce three intermediate scores,
which are aggregated into the final anomaly score. Isconna does not actively
explore or maintain pattern snippets; it instead measures the consecutive
presence and absence of edge records. Isconna is an online algorithm, it does
not keep the original information of edge records; only statistical values are
maintained in a few count-min sketches (CMS). Isconna's space complexity
$O(rc)$ is determined by two user-specific parameters, the size of CMSs. In
worst case, Isconna's time complexity can be up to $O(rc)$, but it can be
amortized in practice. Experiments show that Isconna outperforms five
state-of-the-art frequency- and/or pattern-based baselines on six real-world
datasets with up to 20 million edge records.
