Integration of Machine Learning Algorithms with Knowledge Bases
Funded by Computing Research Association - Women (CRA-W)
About the project
Due to recent advances in computing power and availability of high amounts of labeled and unlabeled data, applications of Machine Learning (ML) have emerged as the dominant form of data-driven, applied Artificial Intelligence (AI). This transformation, which has brought AI out of academic labs, has reshaped it into an area where progress is driven by applications that are of interest to society. Significant advancements have been achieved in research in classification, regression and clustering problems on different application domains like computer vision and natural language processing. However, integration of reasoning capabilities with these data driven approaches remains an open problem. Solving this problem can potentially create AI systems that produce correct decisions based on what the machine has learned from big data, while being guided by commonsense or domain specific reasoning. A common approach is to use graphical data structures known as knowledge bases to store concepts, their relationships and facts known to humans. This CREU project will provide students a project-based learning experience and equip them with research skills in integrating knowledge bases and machine learning algorithms. The project will investigate the following three domain-specific problems using this general approach: detection of attacks in computer networks as captured in honeypot data using knowledge about network traffic patterns; recognizing air traffic patterns (or other movement patterns e.g. of shipping and land vehicles) using knowledge about geopolitical events and characteristics of time of the year; automatically correcting or supporting statements that makes factual claims by learning from related & co-occurring visual data (images & videos) and natural language text (such as found in Wikipedia entries). These areas of the CREU project are highly relevant to the current events in the US and the world and will remain important as technology becomes increasingly complex.
Problem statement and research approach
In many potential application areas of machine learning data can come in many forms from multiple sources. There must be some structural commonality, though, and alignment points for possible data integration. In addition, generally during the preparation of data for machine learning assumes that the models are built based on and for the individual observations/events. In many application areas, however, e.g. cybersecurity, analysis of multiple related observations/events from multiple sources may be necessary. That practically means that there is a need to integrate and aggregate data to build proper machine learning models.
There are challenges with choosing the proper aggregations of data. The groups of events corresponding to aggregations should have appropriate size to differentiate between various categories. With a small group, the sparsity of micro-events may be insufficiently to provide a reliable machine-learning model. With the larger group the machine learning model might be more reliable. At the same time if the group is too large it might not properly reflect the typical individual categories. As we move out to wider groups, these more local effects will have reduced impact on the averages. Hence, there is a tradeoff between sparsity and specificity.
In our project various aggregations will be used for appropriate aggregation of observations/events for machine learning. An aggregation is a way of collecting observations/events into a macro-event and typically assigning some aggregate value to that macro-event, such as count. Many possible ways to aggregate events will be considered. The typical aggregations are by some attribute value, e.g. aggregating events by the same event code. For some time-related data analysis, the machine-learning model might need to be very sensitive to the temporal aberrations. In such case the time limits are typically imposed on at least some aggregations e.g. by a fixed time window or by a fixed number of events.
One of the fundamental operations for a data warehouse is the summarization of the data from a fact table to create new tables. These tables can be obtained by various aggregations of observations/events in the fact table. These new tables are, referred to as summary tables. Summary tables in machine learning applications can also contain information about machine learning models characteristics. It is important, therefore, to develop a systematic method for the design of the hierarchy of summary tables, which results in a systematic method to optimize machine-learning models.
In general, the hierarchy of summary tables can be modeled as a directed acyclic graph (DAG). Let us look at an example of hierarchy of summary tables obtained from our fact table (T01). Level zero is for the fact table itself, which describes all observations/events. The first level consists of summary tables containing information about aggregations obtained from the fact table by reducing it by a single index attribute. We can consider the second level as the one consisting of summary tables containing information about aggregations obtained from the first level by reducing it by an additional index attribute. The reduce operator, referred to as R, is used to indicate what type of the grouping will be used for summarization. The R operator can be represented graphically as a label on the link between the tables e.g. from table T01 to T11. It determines what index attribute will be dropped in the newly created summary table. The second argument for the R operator is the grouping method. For the main summary graph only the simple grouping method based on removing one index attribute will be allowed. This simple grouping method is denoted as "index based".
In general, the number of summarization levels in the summarization graph is equal to the number of index attributes and the number of summary tables on each level can be computed based on all possible combinations for the corresponding subset of index attributes. The highest level corresponds to a single attribute table that contains the maximum summarization. The directed links are showing possible transformations from one table to another. The levels of the summarization graph correspond to various granularities for grouping. The first summarization level corresponds to the least coarse (finest) grouping; the next (second) summarization level corresponds to coarser grouping, etc.
The steps described above can also result in new attributes for each table. These attributes describe the properties of newly created groups. Each group can have various properties assigned to it, e.g. Count property can store the number of events. In our example of the summary table T11, the Count property can be computed by simply counting the number of events in each group. In our project we will describe summary tables and their attributes graphically. The number of groups is determined by possible values of the summary table index attributes. The R operator specifies how each grouping is created. The computation of the property is determined by a computation method. The "Count" computation method allows computing values of the Count property by simply counting the number of events in each group. The "Sum" computation method allows computing values of the CountAll attribute by adding count property for each group. This is equivalent to counting all events in the fact table. It is important to notice that the summary table does store the actual sequence of events (or sequence of sequences of events, etc.) but rather it stores an information summary for an implicit group of events (identified by its index attributes). This information summary is stored in the form of each group's properties.
In our project we will experiment with the general hierarchy graph with its main summary tables using nodes and simple reductions (by one index attribute) as directed links. In the case of time-dependent data, the specific aggregation method can be time window based or event proximity based. In our investigation, while addressing window-based aggregation, we will have different types of windows with two most obvious: fixed-time window and fixed-number-of-events window. We can model a sliding fixed number-of-events window by extending R operator to denote this aggregation properly. The extension is based on requirement that more complex aggregation of events should be here performed i.e. aggregation of all events within the window. Additionally, each window needs to be uniquely identified since we want to perform various window-based computations. The beginning or ending time of window can be used for that purpose.
Deciding about the overlap of sliding windows requires some attention since it will affect the number of aggregations. The extreme case of associating a window with each event is not practical because of the large amount of computations and data (no data reduction), while single events would not affect the total count that much. Another extreme case of making window disjoint is not sufficient since the burst of events divided into two windows might not trigger the anomaly detector. Practically, some overlapping factor needs to be selected, e.g. 50%. As a result, the data contain many redundancies since the same event will be present in many groupings. For the window-overlapping factor 50% the replication that will be close to the replication factor 2.
The information about window-based aggregations can be also stored in a summary table. This new table does not belong to main summarization hierarchy since a complex aggregation was used. It will be placed in the new layer of the node T01. In general, any newly introduced complex aggregation will result in the creation of the new table and new layer of the summarization hierarchy. The new table is placed in that layer in the same node as the main summary table with the same index attributes. The newly created table can be a starting node of a new hierarchy placed in the new layer. Other tables of the new hierarchy would also correspond to main summary tables that have the same index attributes.