Juan Sequeda

University of Texas at Austin | UT · Department of Computer Science

Property graphs have reached a high level of maturity, witnessed by multiple robust graph database systems as well as the ongoing standardization effort aiming at a creating a new standard Graph Query Language (GQL). Yet, despite documented demand, schema support is limited in existing systems. It is anticipated that the second version of the GQL S...

Incomplete data, in the form of null values, has been extensively studied since the inception of the relational model in the 1970s. Anecdotally, one hears that the way in which SQL, the standard language for relational databases, handles nulls creates a myriad of problems in everyday applications of database systems. To the best of our knowledge, h...

SemTab 2021 was the third edition of the Semantic Web Challenge on Tabular Data to Knowledge Graph Matching, successfully collocated with the 20th International Semantic Web Conference (ISWC) and the 16th Ontology Matching (OM) Workshop. SemTab provides a common framework to conduct a systematic evaluation of state-of-the-art systems.

Knowledge graphs (KGs) have emerged as a compelling abstraction for organizing the world's structured knowledge and for integrating information extracted from multiple data sources. They are also beginning to play a central role in representing information extracted by AI systems, and for improving the predictions of AI systems by giving them knowl...

In this article, we provide a comprehensive introduction to knowledge graphs, which have recently garnered significant attention from both industry and academia in scenarios that require exploiting diverse, dynamic, large-scale collections of data. After some opening remarks, we motivate and contrast various graph-based data models, as well as lang...

Organizations across all sectors are increasingly undergoing deep transformation and restructuring towards data-driven operations. The central role of data highlights the need for reliable and clean data. Unreliable, erroneous, and incomplete data lead to critical bottlenecks in processing pipelines and, ultimately, service failures, which are disa...

In this paper we provide a comprehensive introduction to knowledge graphs, which have recently garnered significant attention from both industry and academia in scenarios that require exploiting diverse, dynamic, large-scale collections of data. After a general introduction, we motivate and contrast various graph-based data models and query languag...

In this paper we provide a comprehensive introduction to knowledge graphs, which have recently garnered significant attention from both industry and academia in scenarios that require exploiting diverse, dynamic, large-scale collections of data. After a general introduction, we motivate and contrast various graph-based data models and query languag...

We report on a community effort between industry and academia to shape the future of graph query languages. We argue that existing graph database management systems should consider supporting a query language with two key characteristics. First, it should be composable, meaning, that graphs are the input and the output of queries. Second, the graph...

We report on a community effort between industry and academia to shape the future of graph query languages. We argue that existing graph database management systems should consider supporting a query language with two key characteristics. First, it should be composable, meaning, that graphs are the input and the output of queries. Second, the graph...

Given a source relational database, a target OWL ontology and a mapping from the source database to the target ontology, Ontology-Based Data Access (OBDA) concerns answering queries over the target ontology using these three components. This paper presents the development of UltrawrapOBDA, an OBDA system comprising bidirectional evaluation; that is...

Constitutional design and redesign is constant. Over the last 200 years, countries have replaced their constitutions an average of every 19 years and some have amended them almost yearly. A basic problem in the drafting of these documents is the search and analysis of model text deployed in other jurisdictions. Traditionally, this process has been...

R2RML is used to specify transformations of data available in relational databases into materialised or virtual RDF datasets. SPARQL queries evaluated against virtual datasets are translated into SQL queries according to the R2RML mappings, so that they can be evaluated over the underlying relational database engines. In this paper we describe an e...

Processing large volumes of RDF data requires sophisticated tools. In recent years, much effort was spent on optimizing native RDF stores and on repurposing relational query engines for large-scale RDF processing. Concurrently, a number of new data management systems---regrouped under the NoSQL (for "not only SQL") umbrella---rapidly rose to promin...

QODI is an automatic ontology-based data integration system (OBDI). QODI is distinguished in that the ontology mapping algorithm dynamically determines a partial mapping specific to the reformulation of each query. The query provides application context not available in the ontologies alone; thereby the system is able to disambiguate mappings for d...

The Semantic Web’s promise of web-wide data integration requires the inclusion of legacy relational databases,1 i.e. the execution of SPARQL queries on RDF representation of the legacy relational data. We explore a hypothesis: existing commercial relational databases already subsume the algorithms and optimizations needed to support effective SPARQ...

The Semantic Web is the initiative of the W3C to make information on the Web readable not only by humans but also by machines. RDF is the data model for Semantic Web data, and SPARQL is the standard query language for this data model. RDF also considers a special type of objects to describe anonymous resources, called blank nodes in the RDF data mo...

The W3C Relational Database to RDF (RDB2RDF) standards are positioned to bridge the gap between Relational Databases and the Semantic Web. The standards consist of two interrelated and complementary specifications: Direct Mapping of Relational Data to RDF and R2RML: RDB to RDF Mapping Language. In this paper we present initial results on the formal...

The OWL 2 QL profile, which is based on DL-LiteR, has been designed so that query answering is possible using relational database technology via query rewriting. Unfortunately, given a query Q posed in terms of an OWL 2 QL ontology O, the size of the rewritten query, Q o , which can be evaluated directly on the relational database, is worst case ex...

This paper describes a system, Diamond, which uses the Rete Match algorithm to evaluate SPARQL queries on distributed RDF data in the Linked Data model. In the Linked Data model, as a query is being evaluated, additional linked data can be identified as additional data to be evaluated by the query; the process may re-peat indefinitely. Casting Link...

Diamond is a Rete match based system that evaluates SPARQL queries on Linked Data. The evaluation of SPARQL query predicates is a useful intermediate milestone for a system ultimately intended to sup-port full rule-based inference on Linked Data. A byproduct is the inte-grated graphical rule debugging environment is a first of its kind debug enviro...

Mapping relational databases to RDF is a fundamental problem for the development of the Semantic Web. We present a solution, inspired by draft methods defined by the W3C where relational databases are directly mapped to RDF and OWL. Given a relational database schema and its integrity constraints, this direct mapping produces an OWL ontology, which...

The Semantic Web anticipates integrated access to a large number of information sources on the Internet represented as Resource Description Framework (RDF). Given the large number of websites that are backed by SQL databases, methods that automate the translation of those databases to RDF are crucial. One approach, taken by a number of researchers,...

Research on querying the Web of Data is still in its infancy. In this paper, we provide an initial set of general features that we envision should be considered in order to define a query language for the Web of Data. Furthermore, for each of these features, we pose questions that have not been addressed before in the context of querying the Web of...

Ontologies are commonly used in biomedicine to organize concepts to describe domains such as anatomies, environments, experiment, taxonomies etc. NCBO BioPortal currently hosts about 180 different biomedical ontologies. These ontologies have been mainly expressed in either the Open Biomedical Ontology (OBO) format or the Web Ontology Language (OWL)...

Description: Summary of final mappings, and original independent mappings

In the past two years, the amount of data published in RDF and following the Linked Data principles has increased dramatically. Everyday people are publishing datasets as Linked Data. However, applications that consume Linked Data are not mainstream yet. To overcome this issue, we present a beginners tutorial on consuming Linked Data. We will discu...

Ultrawrap is an automatic wrapping system that synthesizes an OWL ontology from the database's SQL schema and provides SPARQL query services for legacy relational databases. The system intentionally defines triples by using SQL view statements. The benefits of this organization include, the virtualization of the triple table assures real-time consi...

The Open Biomedical Ontology (OBO) format emerged from the Gene Ontology, and now supports many other important ontologies. If we compare OBO to OWL, the ontology language of the Se mantic Web, the latter anticipates integral query languages, rule languages and distributed infrastructure for information interchange. A convenient method for leveragi...

The Semantic Web anticipates rich, integrated access to a large number of information sources on the Internet. Since a large number of websites are backed by SQL databases, methods that automate the integration of these databases with the Semantic Web are crucial. This paper surveys methods used to create ontological descriptions of databases by ex...

This document surveys current techniques, tools and applications for mapping between Relational Databases (RDB) and the Resource Description Framework (RDF). Basic knowledge of RDF as well as RDB

Information coming from sensor networks is being increasingly used in a variety of systems (decision support systems, information portals, etc), normally combined with information coming from more traditional sources (e.g., relational databases, web documents, etc). However, existing ontology based information integration approaches cannot be easil...

The amount of sensors publishing data on the Web is increasing as a result of the online availability of Sensor Web platforms that provide support for this task. With such increase in sensor data publication, new challenges arise for the identification, discovery and access to this data. Following the set of best practices to publish and link struc...

The content of most Web pages is dynamically derived from an un- derlying relational database. Thus, the success of the Semantic Web hinges on enabling access to relational databases and their content by semantic methods. We define a system for automatic transformation of SQL DDL schemas into OWL DL ontologies. This system goes further than earlier...

The vision of the Semantic Web is to create a web of data with well-defined meaning. Most data in the current web is managed by relational databases. Thus, it is imperative for the Semantic Web community to offer easily implemented solutions to bridging relational database content and RDF. Direct mappings means to use the SQL schema to create an OW...

Assuring the quality of software requirement specifications is critical. Poor requirement specifications may make costly errors during the development process. Therefore methods and techniques for verification and validation of software requirement specifications are fundamentally important. This survey presents taxonomy of verification and validat...

Our position is founded on two assumptions. First, we assume that the SQL data definition language (SQL-DDL) is capable of encoding substantial domain semantics, albeit not in ways syntactically accessible to inference engines. Second, the layered architecture of the Semantic Web, a.k.a. the layer cake, transcends the Semantic Web. In other words,...

Integrating relational databases with the Semantic Web can be accom-plish by means of two primary approaches: automatic direct mapping or devel-opers detailing application specific mappings. Both approaches are the subject of the W3C Relational Database to RDF (RDB2RDF) Working Group. Intuitively, a direct mapping is a default and automatic way to...

Relational Database to RDF (RDB2RDF) systems executes SPARQL queries on the relational data. Past studies have shown that RDB2RDF systems do not perform well, in other words, the execution time of a SPARQL query on a RDB2RDF system compared to its semantically equivalent SQL query is much slower. Therefore, we ask ourselves, what optimizations are...

In this paper we describe a two-step approach for the publication of data about displaced people in Colombia, whose lack of homogeneity represents a major barrier for the application of adequate policies. This data is available in heterogeneous data sources, mainly relational, and is not connected to social networking sites. Our approach consists i...