Mathias Niepert

Leveraging terminological structure for object reconciliation

It has been argued that linked open data is the major benefit of semantic technologies for the web as it provides a huge amount of structured data that can be accessed in a more effective way than web pages. While linked open data avoids many problems connected with the use of expressive ontologies such as the knowledge acquisition bottleneck, data heterogeneity remains a challenging problem. In particular, identical objects may be referred to by different URIs in different data sets. Identifying such representations of the same object is called object reconciliation. In this paper, we propose a novel approach to object reconciliation that is based on an existing semantic similarity measure for linked data. We adapt the measure to the object reconciliation problem, present exact and approximate algorithms that efficiently implement the methods, and provide a systematic experimental evaluation based on a benchmark dataset. As our main result, we show that the use of light-weight ontologies and schema information significantly improves object reconciliation in the context of linked open data.

Probabilistic optimization of semantic process model matching

Business process models are increasingly used by companies, often yielding repositories of several thousand models. These models are of great value for business analysis such as service identification or process standardization. A problem is though that many of these analyses require the pairwise comparison of process models, which is hardly feasible to do manually given an extensive number of models. While the computation of similarity between a pair of process models has been intensively studied in recent years, there is a notable gap on automatically matching activities of two process models. In this paper, we develop an approach based on semantic techniques and probabilistic optimization. We evaluate our approach using a sample of admission processes from different universities.

Log-linear description logics

Log-linear description logics are a family of probabilistic logics integrating various concepts and methods from the areas of knowledge representation and reasoning and statistical relational AI. We define the syntax and semantics of log-linear description logics, describe a convenient representation as sets of first-order formulas, and discuss computational and algorithmic aspects of probabilistic queries in the language. The paper concludes with an experimental evaluation of an implementation of a log-linear DL reasoner.

From encyclopedia to ontology: toward dynamic representation of the discipline of philosophy

The application of digital humanities techniques to philosophy is changing the way scholars approach the discipline. This paper seeks to open a discussion about the difficulties, methods, opportunities, and dangers of creating and utilizing a formal representation of the discipline of philosophy. We review our current project, the Indiana Philosophy Ontology (InPhO) project, which uses a combination of automated methods and expert feedback to create a dynamic computational ontology for the discipline of philosophy. We argue that our distributed, expert-based approach to modeling the discipline carries substantial practical and philosophical benefits over alternatives. We also discuss challenges facing our project (and any other similar project) as well as the future directions for digital philosophy afforded by formal modeling.

ELOG: a probabilistic reasoner for OWL EL

Log-linear description logics are probabilistic logics combining several concepts and methods from the areas of knowledge representation and reasoning and statistical relational AI. We describe some of the implementation details of the log-linear reasoner ELOG. The reasoner employs database technology to dynamically transform inference problems to integer linear programs (ILP). In order to lower the size of the ILPs and reduce the complexity we employ a form of cutting plane inference during reasoning.

Logical and algorithmic properties of stable conditional independence

The logical and algorithmic properties of stable conditional independence (CI) as an alternative structural representation of conditional independence information are investigated. We utilize recent results concerning a complete axiomatization of stable conditional independence relative to discrete probability measures to derive perfect model properties of stable conditional independence structures. We show that stable CI can be interpreted as a generalization of Markov networks and establish a connection between sets of stable CI statements and propositional formulas in conjunctive normal form. Consequently, we derive that the implication problem for stable CI is coNP-complete. Finally, we show that Boolean satisfiability (SAT) solvers can be employed to efficiently decide the implication problem and to compute concise, non-redundant representations of stable CI, even for instances involving hundreds of random variables.

Probabilistic-logical web data integration

The integration of both distributed schemas and data repositories is a major challenge in data and knowledge management applications. Instances of this problem range from mapping database schemas to object reconciliation in the linked open data cloud. We present a novel approach to several important data integration problems that combines logical and probabilistic reasoning. We first provide a brief overview of some of the basic formalisms such as description logics and Markov logic that are used in the framework. We then describe the representation of the different integration problems in the probabilistic-logical framework and discuss efficient inference algorithms. For each of the applications, we conducted extensive experiments on standard data integration and matching benchmarks to evaluate the efficiency and performance of the approach. The positive results of the evaluation are quite promising and the flexibility of the framework makes it easily adaptable to other realworld data integration problems.

A Statistical-Relational Activity Recognition Framework for Ambient Assisted Living Systems

Smart environments with ubiquitous sensing technologies are a promising perspective for reliable and continuous healthcare systems with reduced costs. A primary challenge for such assisted living systems is the automated recognition of everyday activities carried out by humans in their own home. In this work, we investigate the use of Markov Logic Networks as a framework for activity recognition within intelligent home-like environments equippedwith pervasive light-weight sensor technologies. In particular, we explore the ability of MLNs to capture temporal relations and background knowledge for improving the recognition performance.

On the completeness of the semigraphoid axioms for deriving arbitrary from saturated conditional independence statements

Conditional independence (CI) statements occur in several areas of computer science and artificial intelligence, e.g., as embedded multivalued dependencies in database theory, disjunctive association rules in data mining, and probabilistic CI statements in probability theory. Although, syntactically, such constraints can always be represented in the form I(A,B|C), with A, B, and C subsets of some universe S, their semantics is very dependent on their interpretation, and, therefore, inference rules valid under one interpretation need not be valid under another. However, all aforementioned interpretations obey the so-called semigraphoid axioms. In this paper, we consider the restricted case of deriving arbitrary CI statements from so-called saturated ones, i.e., which involve all elements of S. Our main result is a necessary and sufficient condition under which the semigraphoid axioms are also complete for such derivations. Finally, we apply these results to the examples mentioned above to show that, for these semantics, the semigraphoid axioms are both sound and complete for the derivation of arbitrary CI statements from saturated ones.

Thesaurus extension using web search engines

Maintaining and extending large thesauri is an important challenge facing digital libraries and IT businesses alike. In this paper we describe a method building on and extending existing methods from the areas of thesaurus maintenance, natural language processing, and machine learning to (a) extract a set of novel candidate concepts from text corpora and (b) to generate a small ranked list of suggestions for the position of these concept in an existing thesaurus. Based on a modification of the standard tf-idf term weighting we extract relevant concept candidates from a document corpus. We then apply a pattern-based machine learning approach on content extracted from web search engine snippets to determine the type of relation between the candidate terms and existing thesaurus concepts. The approach is evaluated with a largescale experiment using the MeSH and WordNet thesauri as testbed.