Werner Nutt

• Free University of Bozen-Bolzano

This paper studies the completeness of conjunctive queries over a partially complete database and the approximation of incomplete queries. Given a query and a set of completeness rules (a special kind of tuple generating dependencies) that specify which parts of the database are complete, we investigate whether the query can be fully answered, as i...

Construction sites are among the most hazardous workplaces. To reduce accidents, it is required to identify risky situations beforehand, and to describe which countermeasures to put in place. In this paper, we investigate possible techniques to support the identification of risky activities and potential hazards associated with those activities. Mo...

General purpose process modeling approaches are meant to be applicable to a wide range of domains. To achieve this result, their constructs need to be general, thus failing in capturing the peculiarities of a particular application domain. One aspect usually neglected is the representation of the items on which activities are to be executed. As a c...

CoPMod is a proof-of-concept tool for supporting a collaborative construction process modeling approach that has been developed in a research project and tested in real construction projects. In the tests, the approach was applied using a semi-formal graphical modeling language and drawing models on whiteboards. CoPMod is the first IT solution to s...

Digitalization could support the execution of construction processes resulting in a decrease of waste and a better synchronization with the supply chain. However, in construction the level of digitalization is low, also compared to other sectors. This is due to some characteristics of the sector, such as the limited margins of Small and Medium-size...

Knowledge bases (KBs) are not static entities: new information constantly appears and some of the previous knowledge becomes obsolete. In order to reflect this evolution of knowledge, KBs should be expanded with the new knowledge and contracted from the obsolete one. This problem is well-studied for propositional but much less for first-order KBs....

Digitalization could support the execution of construction processes resulting in a decrease of waste and a better synchronization with the supply chain. However, in construction the level of digitalization is low, also compared to other sectors. This is due to some characteristics of the sector, such as the limited margins of Small and Medium-size...

Process modeling has been widely investigated in the literature and several general purpose approaches have been introduced, addressing a variety of domains. However, generality goes to the detriment of the possibility to model details and peculiarities of a particular application domain. As acknowledged by the literature, known approaches predomin...

Completeness is a crucial data quality aspect that deals with the question: do we have all the data we need? The lack of awareness on the completeness state of a knowledge graph (KG) may result in bias or even falsity for any decisions made based on the KG. Given a KG, one may be wondering how its completeness may vary across different topics. In t...

Knowledge bases (KBs) are not static entities: new information constantly appears and some of the previous knowledge becomes obsolete. In order to reflect this evolution of knowledge, KBs should be expanded with the new knowledge and contracted from the obsolete one. This problem is well-studied for propositional but much less for first-order KBs....

Most news summarization techniques are static, and thus do not satisfy user needs in having summaries with specific structures or details. Meanwhile, existing dynamic techniques such as query-based summarization fail to handle content-independent queries that target the type of summary information such as time, location, reasons, and consequences o...

Recent knowledge extraction methods are moving towards ternary and higher-arity relations to capture more information about binary facts. An example is to include the time, the location, and the duration of a specific fact. These relations can be even more complex to extract in advanced domains such as news, where events typically come with differe...

The Semantic Web is commonly interpreted under the open-world assumption, meaning that information available (e.g., in a data source) captures only a subset of the reality. Therefore, there is no certainty about whether the available information provides a complete representation of the reality. The broad aim of this article is to contribute a form...

Summarizing news articles is becoming crucial for allowing quick and concise access to information about daily events. This task can be challenging when the same event is reported with various levels of detail or is subject to diverse view points. A well established technique in the area of news summarization consists in modeling events as a set of...

The collaborative knowledge base Wikidata is the central storage of Wikimedia projects, containing over 45 million data items. It acts as the hub for interlinking Wikipedia pages about a specific item in different languages, automates features such as infoboxes in Wikipedia, and is increasingly used for other applications such as data enrichment an...

Situation faced: Frener and Reifer (F&R) is a leader in engineering, fabricating, and installing facades with non-standard designs. The company was looking for comprehensive, domain-specific approaches to improve the company’s control over facade processes, from design to execution and monitoring. What makes process management particularly challeng...

In knowledge bases such as Wikidata, it is possible to assert a large set of properties for entities, ranging from generic ones such as name and place of birth to highly profession-specific or background-specific ones such as doctoral advisor or medical condition. Determining a preference or ranking in this large set is a challenge in tasks such as...

Compared to other industries the construction industry (CI) is highly fragmented and suffers from a low productivity rate, a weak usage of resources and delays. Due to a poor collaboration, construction processes are inefficient, affecting negatively budget and schedule. Most projects in construction are “one-of-a-kind”, which are characterized by...

In knowledge bases such as Wikidata, it is possible to assert a large set of properties for entities, ranging from generic ones such as name and place of birth to highly profession-specific or background-specific ones such as doctoral advisor or medical condition. Determining a preference or ranking in this large set is a challenge in tasks such as...

Engineer-to-Order (ETO) process chain types with a successive installation on-site are common in plant building and the construction industry. Usually, the core processes Engineering, Fabrication and Installation are disconnected, which creates high levels of Work in Progress (WIP) and long lead-times. Furthermore, up to date information about the...

Nowadays, more and more RDF data is becoming available on the Semantic Web. While the Semantic Web is generally incomplete by nature, on certain topics, it already contains complete information and thus, queries may return all answers that exist in reality. In this paper we develop a technique to check query completeness based on RDF data annotated...

Conjunctive database queries have been extended with a mechanism for object creation to capture important applications such as data exchange, data integration, and ontology-based data access. Object creation generates new object identifiers in the result, that do not belong to the set of constants in the source database. The new object identifiers...

Nowadays, more and more RDF data is becoming available on the Semantic Web. While the Semantic Web is generally incomplete by nature, on certain topics, it already contains complete information and thus, queries may return all answers that exist in reality. In this paper we develop a technique to check query completeness based on RDF data annotated...

Organizations continuously accumulate data, often according to some business processes. If one poses a query over such data for decision support, it is important to know whether the query is stable, that is, whether the answers will stay the same or may change in the future because business processes may add further data. We investigate query stabi...

The paper describes a framework for efficiently organizing and managing construction projects, aimed at reducing time and cost overruns. The approach provides concepts and tools to constantly monitor the actual progress of a project, so as to identify problems early on and to take corrective action by replanning and rescheduling. The framework comb...

News websites give their users the opportunity to participate in discussions about published articles, by writing comments. Typically, these comments are unstructured making it hard to understand the flow of user discussions. Thus, there is a need for organizing comments to help users to (1) gain more insights about news topics, and (2) have an eas...

Data completeness is commonly regarded as one of the key aspects of data quality. With this paper we make two main contributions: (i) we develop techniques to reason about the completeness of a query answer over a partially complete database, taking into account constraints that hold over the database, and (ii) we implement them by an encoding into...

In many applications including loosely coupled cloud databases, collaborative editing and network monitoring, data from multiple sources is regularly used for query answering. For reasons such as system failures, insufficient author knowledge or network issues, data may be temporarily unavailable or generally nonexistent. Hence, not all data needed...

Real-life spatial databases are inherently incomplete. This is in particular the case when data from different sources are combined. An extreme example are volunteered geographical information systems like OpenStreetMap. When querying such databases the question arises how reliable are the retrieved answers. For instance, for positive queries, whic...

RDF data is often treated as incomplete, following the Open-World Assumption. On the other hand, SPARQL, the standard query language over RDF, usually follows the Closed-World Assumption, assuming RDF data to be complete. This gives rise to a semantic gap between RDF and SPARQL. In this paper, we address how to close the semantic gap between RDF an...

With the increased availability of data on the Semantic Web, the question whether data sources offer data of appropriate quality for a given purpose becomes an issue. With CORNER, we specifically address the data quality aspect of completeness. CORNER supports SPARQL BGP queries and can take RDFS ontologies into account in its analysis. If a query...

Databases are traditionally considered either under the closedworld or the open-world assumption. In some scenarios however a middle ground, the partial closed-world assumption, is needed, which has received less attention so far. In this survey we review foundational and work on the partial closed-world assumption and then discuss work done in our...

With thousands of RDF data sources available on the Web covering disparate and possibly overlapping knowledge domains, the problem of providing high-level descriptions (in the form of metadata) of their content becomes crucial. In this paper we introduce a theoretical framework for describing data sources in terms of their completeness. We show how...

We present a system that computes for a query that may be incomplete, complete approximations from above and from below. We assume a setting where queries are posed over a partially complete database, that is, a database that is generally incomplete, but is known to contain complete information about specific aspects of its application domain. Whic...

Geographical databases are often incomplete, especially when built up incrementally and by volunteers. A prominent example is OpenStreetMap. Often such databases contain also metadata saying that certain features are completely captured for certain areas. We show how to use such metadata to analyse in which areas queries return a complete answer. S...

Data completeness is an essential aspect of data quality, and has in turn a huge impact on the effective management of companies. For example, statistics are computed and audits are conducted in companies by implicitly placing the strong assumption that the analysed data are complete. In this work, we are interested in studying the problem of compl...

Data completeness is an essential aspect of data quality, and has in turn a huge impact on the effective management of companies. For example, statistics are computed and audits are conducted in companies by implicitly placing the strong assumption that the analysed data are complete. In this work, we are interested in studying the problem of compl...

With thousands of RDF data sources today available on the Web, cov-ering disparate and possibly overlapping knowledge domains, the problem of pro-viding high-level descriptions (in the form of metadata) of their content becomes crucial. In this paper we introduce a theoretical framework for describing data sources in terms of their completeness. We...

Data completeness is an important aspect of data quality. We consider a setting, where databases can be incomplete in two ways: records may be missing and records may contain null values. We (i) formalize when the answer set of a query is complete in spite of such incompleteness, and (ii) we introduce table completeness statements, by which one can...

MAGIK demonstrates how to use meta-information about the completeness of a database to assess the quality of the answers returned by a query. The system holds so-called table-completeness (TC) statements, by which one can express that a table is partially complete, that is, it contains all facts about some aspect of the domain. Given a query, MAGIK...

Data completeness is an essential aspect of data quality as in many scenarios it is crucial to guarantee the completeness of query answers. Data might be incomplete in two ways: records may be missing as a whole, or attribute values of a record may be absent, indicated by a null. We extend previous work by two of the authors [10] that dealt only wi...

Sources of data uncertainty and imprecision are numerous. A way to handle this uncertainty is to associate probabilistic annotations to data. Many such probabilistic database models have been proposed, both in the relational and in the semi-structured setting. The latter is particularly well adapted to the management of uncertain data coming from a...

Production systems are an established paradigm in knowledge representation, while ontologies are widely used to model and reason about the domain of an application. Description logics, underlying for instance the Web ontology language OWL, are a well-studied formalism to express ontologies. In this work we combine production systems (ps) and Descri...

Data completeness is an important aspect of data quality as in many scenarios it is crucial to guarantee completeness of query answers. We develop techniques to conclude the completeness of query answers from information about the completeness of parts of a generally incomplete database. In our framework, completeness of a database can be described...

We study the problem of query completeness (QC) over partially complete databases. Query completeness is an important goal of data quality assurance. Incomplete databases can occur in many contexts, especially whenever many users are supposed to insert data into the same database. Although the overall data can often not be guaranteed to be complete...

We address the cost of adding value joins to tree-pattern queries and monadic second-order queries over trees in terms of the tractability of query evaluation over two data models: XML and probabilistic XML. Our results show that the data complexity rises from linear, for join-free queries, to intractable, for queries with value joins, while combin...

Biological scientists have made large amounts of data available on the Web, which can be accessed by canned or precomputed queries presented via web forms. To satisfy further information needs, users currently have to have a good understanding of SQL and how the data is stored in the database. While accessing information at the ontological layer se...

We study the problem of evolution for Knowledge Bases (KBs) expressed in Description Logics (DLs) of the DL-Lite family. DL-Lite is at the basis of OWL 2 QL, one of the tractable fragments of OWL 2, the recently proposed revision of the Web Ontology Language. We propose some fundamental principles that KB evolution should respect. We review known m...

We study the problem of instance level (ABox) updates for Knowledge Bases (KBs) represented in Description Logics of the DL-Lite family. DL-Lite is at the basis of OWL 2 QL, one of the tractable fragments of OWL 2, the recently proposed revision of the Web Ontology Language. We examine known works on updates that follow the model-based approach and...

Sources of data uncertainty and imprecision are numerous. A way to handle this uncertainty is to associate probabilistic annotations to data. Many such probabilistic database models have been proposed, both in the relational and in the semi-structured setting. The latter is particularly well adapted to the management of uncertain data coming from a...

We investigate the complexity of performing updates on probabilistic XML data for various classes of probabilistic XML documents of different succinctness. We consider two elementary kinds of updates, insertions and deletions, that are defined with the help of a locator query that specifies the nodes where the update is to be performed. For inserti...

Many kinds of information, such as addresses, crawls of webpages, or academic affiliations, are prone to becoming outdated over time. Therefore, in some applications, updates are performed periodically in order to keep the correctness and usefulness of such information high. As refreshing information usually has a cost, e.g. computation time, netwo...

We study the problem of updates for TBoxes represented in Description Logics of the DL-Lite family. DL-Lite is at the basis of OWL 2 QL, one of the tractable fragments of OWL 2, the recently proposed revision of the Web Ontology Language. In this paper, we address for the first time the problem of updating TBoxes. We propose some principles that TB...

Les sources d'incertitude et d'imprécision des données sont nombreuses. Une ma-nière de gérer cette incertitude est d'associer aux données des annotations probabi-listes. De nombreux modèles de bases de données probabilistes ont ainsi été proposés, dans les cadres relationnel et semi-structuré. Ce dernier est particulièrement adapté à la gestion de...

Answering queries over ontologies is an important issue for the Semantic Web. Aggregate queries were widely studied for relational databases but almost no results are known for aggregate queries over ontologies. In this work we in- vestigate the latter problem. We propose syntax and se- mantics for epistemic aggregate queries over ontologies and st...

Information integration is becoming a critical problem for both businesses and individuals. The data, especially the one that comes from the Web, is naturally incomplete, that is, some data values may be unknown or lost because of communication problems, hidden due to privacy considerations. At the same time research in (virtual) integration in the...

Purpose – Distributed data streams are an important topic of current research. In such a setting, data values will be missed, e.g. due to network errors. This paper aims to allow this incompleteness to be detected and overcome with either the user not being affected or the effects of the incompleteness being reported to the user. Design/methodology...

Equivalence of aggregate queries is investigated for the class of conjunctive queries with comparisons and the aggregate operators count, count-distinct, min, max, and sum. Essentially, this class contains unnested SQL queries with the above aggregate operators, with a where clause con- sisting of a conjunction of comparisons, and without a having...

We study containment of conjunctive queries that are evaluated over databases that may contain tuples with null values. We assume the semantics of SQL for single block queries with a SELECT DISTINCT clause. This problem (“null containment” for short) is different from containment over databases without null values and sometimes more difficult. We s...

In contrast to traditional database queries, a query on stream data is continuous in that it is periodically evaluated over fractions (sliding windows) of the data stream. This introduces challenges beyond those encountered when processing traditional queries. Over a traditional DBMS (Database Management System), the answer to an aggregate query is...

In this work we propose an alternative approach to inference in DL- Lite, based on a reduction to reasoning in an extension of function-free Horn Logic (EHL). We develop a calculus for EHL and prove its soundness and com- pleteness. We also show how to achieve decidability by means of a specific strat- egy, and how alternative strategies can lead t...

There is a wide variety of data, both static and streaming, being published on and about computing Grids. However one aspect of Grid data that has received relatively little attention thus far is that of incompleteness. With potentially many data sources available to choose from, each with its own limitations in terms of coverage of data sets and o...

The problem of rewriting aggregate queries using views is studied for conjunctive queries with arbitrary aggregation functions and built-in predicates. Two types of queries over views are intro- duced for rewriting aggregate queries: pure candidates and aggregate candidates. Pure candidates can be used to rewrite arbitrary aggregate queries. Aggreg...

We study containment of conjunctive queries that are evalu- ated over databases that may contain tuples with null values. We assume the semantics of SQL for single block queries with a SELECT DISTINCT clause. This problem ("null containment" for short) is dierent from containment over databases without null values and sometimes more dif- ficult. We...

Streams of data often originate from many distributed sources. A user wanting to query the streams should not need to know from where each stream originates but should be provided with a global view of the streams. R-GMA is a system that integrates distributed data streams to provide a global view of all the streams for users to query. R-GMA has be...

Over a traditional database management system (DBMS), the answer to an aggregate query is usually much smaller than the answer to a similar non-aggregate query. Therefore, we call such a query "condensative". Current proposals for declarative query languages over data streams do not support such condensative querying. In order to make existing stre...

In data stream applications, streams typically arise from a geographically distributed collection of producers and may be queried by consumers, which may be distributed as well. In such a setting, a query can be seen as a subscription asking to be informed of all tuples that satisfy a specific condition. We propose to support the publishing and que...

R-GMA (Relational Grid Monitoring Architecture) [1] is a grid monitoring and information system that provides a global view of data distributed across a grid system. R-GMA creates the impression of a single centralised repository of information, but in reality the information can be stored at many different locations on the grid. The Registry and S...

We present a publish/subscribe framework for integrating data streams published by distributed producers. We introduce the idea of republishers which merge a set of data streams, either from producers or other republishers. The resulting hierarchy of producers and republishers can then be used to answer consumer queries over the streams. We discuss...

Grids are distributed systems that provide access to computational resources in a transparent fashion. Providing information about the status of the Grid itself is called Grid monitoring. As an approach to this problem, we present the Relational Grid Monitoring Architecture (R-GMA), which tackles Grid monitoring as an information integration proble...

We have developed and implemented the Relational Grid Monitoring Architecture (R-GMA) as part of the DataGrid project, to provide a flexible information and monitoring service for use by other middleware components and applications. R-GMA presents users with a virtual database and mediates queries posed at this database: users pose queries against...

The R-GMA (Relational Grid Monitoring Architecture) was developed within the EU DataGrid project, to bring the power of SQL to an information and monitoring system for the grid. It provides producer and consumer services to both publish and retrieve information from anywhere within a grid environment. Users within a Virtual Organization may define...

We describe how the R-GMA (Relational Grid Monitoring Architecture) can be used to allow for instrument monitoring in a Grid environment. The R-GMA has been developed within the European DataGrid Project (EDG) as a Grid Information and Monitoring System. It is based on the Grid Monitoring Architecture (GMA) from the Global Grid Forum (GGF), which i...

R-GMA is a realization of the Grid Monitoring Architecture (GMA) that also exploits the power of the relational data model and the SQL query language. The biggest challenge during the development of R-GMA was to ensure that it could be scaled to operate in a large grid reliably. The system is being used in areas as diverse as resource discovery, jo...

We describe R-GMA (Relational Grid Monitoring Architecture) which has been developed within the European DataGrid Project as a Grid Information and Monitoring System. Is is based on the GMA from GGF, which is a simple Consumer-Producer model. The special strength of this implementation comes from the power of the relational model. We offer a global...

In F. Baader, D. Calvanese, D. McGuinness, D. Nardi, and P. F. Patel-Schneider, editors.

We describe R-GMA (Relational Grid Monitoring Architecture) which is being developed within the European DataGrid Project as an Grid Information and Monitoring System. Is is based on the GMA from GGF, which is a simple Consumer-Producer model. The special strength of this implementation comes from the power of the relational model. We offer a globa...

Semistructured data occur in situations where information lacks a homogeneous structure and is incomplete. Yet, up to now the incompleteness of information has not been reflected by special features of query languages. Our goal is to investigate the principles of queries that allow for incomplete answers.

We have developed and implemented QUEST---a system for QUErying Semantically Tagged documents on the World-Wide Web. The advent of new markup languages like xml makes it likely that documents on the Web are not simple html documents, but contain in addition objects that represent the semantic structure of the document.

The principles of queries that allow incomplete answers are presented. Partial answers make it necessary to refine the model of query evaluation. The first modification relates to the satisfaction of conditions, under some circumstances, conditions involving unbound variables as satisfied are considered. Second, in order to prevent a proliferation...

Query equivalence is investigated for disjunctive aggregate queries with negated subgoals, constants and comparisons. A full characterization of equivalence is given for the aggregation functions count, max, sum, prod, toptwo and parity. A related problem is that of determining, for a given natural number N, whether two given queries are equivalent...

The problem of deciding containment among aggregate queries is investigated. Containment is reduced to equivalence for queries with expandable aggregation functions. Many common aggregation functions, such as max, cntd (count distinct), count, sum, avg (average), median and stdev (standard deviation) are shown to be expandable. It is shown that eve...

Semistructured data occur in situations where information lacks a homogeneous structure and is incomplete. Yet, up to now the incompleteness of information has not been reflected by special features of query languages. Our goal is to investigate the principles of queries that allow for incomplete answers. We do not present, however, a concrete quer...

EquiX is a search language for XML that combines the power of querying with the simplicity of searching. Requirements for such languages are discussed, and it is shown that EquiX meets the necessary criteria. Both a graph-based abstract syntax and a formal concrete syntax are presented for EquiX queries. In addition, the semantics is defined and an...

Queries involving aggregation are typical in database applications. One of the main ideas to optimize the execution of an aggregate query is to reuse results of previously answered queries. This leads to the problem of rewriting aggregate queries using views. Due to a lack of theory, algorithms for this problem were rather ad-hoc. They were sound,...