Statistical Relational Artificial Intelligence. Luc De Raedt

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1.4 APPLICATIONS OF STARAI

      StarAI has been successfully applied to problems in citation analysis, web mining, natural language processing, robotics, medicine bio- and chemo-informatics, electronic games, and activity recognition, among others. Let us illustrate using a few examples.

      Example 1.2 Mining Electronic Health Records (EHRs) As of today, EHRs hold over 50 years of recorded patient information and, with increased adoption and high levels of population coverage, are becoming the focus of public health analyses. Mining EHR data can lead to improved predictions and better disease characterization. For instance, Coronary Heart Disease (CHD) is a major cause of death worldwide. In the U.S., CHD is responsible for approximated 1 in every 6 deaths with a coronary event occurring every 25 s and about 1 death every minute based on data current to 2007. Although a multitude of cardiovascular risks factors have been identified, CHD actually reflects complex interactions of these factors over time. Thus, early detection of risks will help in designing effective treatments targeted at youth in order to prevent cardiovascular events in adulthood and to dramatically reduce the costs associated with cardiovascaular dieases.

      Figure 1.3: Electronic Health Records (EHRs) are relational databases capturing noisy and missing information with probabilistic dependencies (the black arrows) within and across tables.

      Doing so, however, calls for StarAI. As illustrated in Fig. 1.3, EHR data consists of several diverse features (e.g., demographics, psychosocial, family history, dietary habits) that interact with each other in many complex ways making it relational. Moreover, like most data sets from biomedical applications, EHR data contains missing values, i.e., all data are not collected for all individuals. And, EHR data is often collected as part of a longitudinal study, i.e., over many different time periods such as 0, 5, 10 years, etc., making it temporal. Natarajan et al. [2013] demonstrated that StarAI can uncover complex interactions of risk factors from EHRs. The learned probabilistic relational model performed significantly better than traditional non-relational approaches and conforms to some known or hypothesized medical facts. For instance, it is believed that females are less prone to cardiovascular issues than males. The relational model identifies sex as the most important feature. Similarly, in men, it is believed that the low- and high-density lipoprotein cholesterol levels are very predictive, and the relational model confirms this. For instance, the risk interacts with a (low-density lipoprotein) cholesterol level in year 0 (of the study) for a middle-aged male in year 7, which can result in a relational conditional probability

      Figure 1.4: Populating a knowledge base with probabilistic facts (or assertions) extracted from dark data (e.g., text, audio, video, tables, diagrams, etc.) and background knowledge.

      The model also identifies complex interaction between risk factors at different years of the longitudinal study. For instance, smoking in year 5 interacts with cholesterol level in later years in the case of females, and the triglyceride level in year 5 interacts with the cholesterol level in year 7 for males. Finally, using data such as the age of the children, whether the patients owns or rents a home, their employment status, salary range, their food habits, their smoking and alcohol history, etc., revealed striking socio-economic impacts on the health state of the population.

      Example 1.3 Extracting value from dark data Many companies’ databases include natural language comments buried in tables and spreadsheets. Similarly, there are often tables and figures embedded in documents and web pages. Like dark matter, dark data is this great mass of data buried in text, tables, figures, and images, which lacks structure and so is essentially unprocessable by traditional methods. StarAI helps bring dark data to light (see, e.g., [Niu et al., 2012, Venugopal et al., 2014]), making the knowledge base construction, as illustrated in Fig. 1.4 feasible. The resulting relational probabilistic models are richly structured with many different entity types with complex interactions.

      To carry out such a task, one starts with transforming the dark data such as text documents into relational data. For example, one may employ standard NLP tools such as logistic regression, conditional random fields and dependency parsers to decode the structure (e.g., part-of-speech tags and parse trees) of the text or run some pattern matching techniques to identify candidate entity mentions and then store them in a database. Then, every tuple in the database or result of an database query is a random variable in a relational probabilistic model. The next step is to determine which of the individuals (entities) are the same as each other and same as the entities that are already known about. For instance, a mention of an entity may correspond to multiple candidate entities known from some other database such as Freebase. To determine which entity is correct, one may use the heuristic that “if the string of a mention is identical to the canonical name of an entity, then this mention is likely to refer to this entity.” In the relational probabilistic model, this may read as the quantified conditional probability statement:

      Given such conditional probabilities, the marginal probability of every tuple in the database as well as all derived tuples such as entityMentioned can be inferred.

      We can also model the relationship between learned features using rich linguistic features for trigger and argument detection and type labeling using weighted logical formulae (defined in Chapter 3) such as:

      For each sentence, this assigns probability to the join of a word at some position in a sentence and the dependency type label that connects the word token to the argument token in the dependency parse tree with the trigger types and argument types of the two tokens. Here, triggerType denotes the prediction from a pre-trained support vector machine for triggering some information extracted from the text. This way, high-dimensional, sophisticated features become available to the relational probabilistic model. Moreover, as with Google’s Knowledge Vault [Dong et al., 2014], the parameters of the relational probabilistic model or even (parts) of its structure can be learned from data.

      Example 1.4 Language modeling The aim of language modeling is to estimate a distribution over words that best represents the text of a corpus. This is central to speech recognition, machine translation, and text generation, among others, and the parameters of language models are commonly used as features or as initialization for other natural language processing approaches. Examples include the word distributions learned by probabilistic topic models, or the word embeddings learned through neural language models. In practice, however, the size of the vocabulary traditionally limited the distributions applicable for this task: specifically, one has to either resort to local optimization methods, such as those used in neural language models, or work with heavily constrained distributions. Jernite et al. [2015] overcame these limitations. They model the entire corpus as an undirected graphical model, whose structure is illustrated in Fig. 1.5. Because of parameter sharing in the model, each of the random variables is indistinguishable and by exploiting this symmetry, Jernite et al. derived an efficient approximation of the partition function using lifted variational inference with complexity СКАЧАТЬ