Semantic Tagging on Historical Maps

Tags assigned by users to shared content can be ambiguous. As a possible solution, we propose semantic tagging as a collaborative process in which a user selects and associates Web resources drawn from a knowledge context. We applied this general technique in the specific context of online historical maps and allowed users to annotate and tag them. To study the effects of semantic tagging on tag production, the types and categories of obtained tags, and user task load, we conducted an in-lab within-subject experiment with 24 participants who annotated and tagged two distinct maps. We found that the semantic tagging implementation does not affect these parameters, while providing tagging relationships to well-defined concept definitions. Compared to label-based tagging, our technique also gathers positive and negative tagging relationships. We believe that our findings carry implications for designers who want to adopt semantic tagging in other contexts and systems on the Web.Comment: 10 page

A Web-based mapping technique foreEstablishing metadata interoperability

Die Integration von Metadaten aus unterschiedlichen, heterogenen Datenquellen erfordert Metadaten-Interoperabilität, eine Eigenschaft die nicht standardmäßig gegeben ist. Metadaten Mapping Verfahren ermöglichen es Domänenexperten Metadaten-Interoperabilität in einem bestimmten Integrationskontext herzustellen. Mapping Lösungen sollen dabei die notwendige Unterstützung bieten. Während diese für den etablierten Bereich interoperabler Datenbanken bereits existieren, ist dies für Web-Umgebungen nicht der Fall. Betrachtet man das Ausmaß ständig wachsender strukturierter Metadaten und Metadatenschemata im Web, so zeichnet sich ein Bedarf nach Web-basierten Mapping Lösungen ab. Den Kern einer solchen Lösung bildet ein Mappingmodell, das die zur Spezifikation von Mappings notwendigen Sprachkonstrukte definiert. Existierende Semantic Web Sprachen wie beispielsweise RDFS oder OWL bieten zwar grundlegende Mappingelemente (z.B.: owl:equivalentProperty, owl:sameAs), adressieren jedoch nicht das gesamte Sprektrum möglicher semantischer und struktureller Heterogenitäten, die zwischen unterschiedlichen, inkompatiblen Metadatenobjekten auftreten können. Außerdem fehlen technische Lösungsansätze zur Überführung zuvor definierter Mappings in ausführbare Abfragen. Als zentraler wissenschaftlicher Beitrag dieser Dissertation, wird ein abstraktes Mappingmodell präsentiert, welches das Mappingproblem auf generischer Ebene reflektiert und Lösungsansätze zum Abgleich inkompatibler Schemata bietet. Instanztransformationsfunktionen und URIs nehmen in diesem Modell eine zentrale Rolle ein. Erstere überbrücken ein breites Spektrum möglicher semantischer und struktureller Heterogenitäten, während letztere das Mappingmodell in die Architektur des World Wide Webs einbinden. Auf einer konkreten, sprachspezifischen Ebene wird die Anbindung des abstrakten Modells an die RDF Vocabulary Description Language (RDFS) präsentiert, wodurch ein Mapping zwischen unterschiedlichen, in RDFS ausgedrückten Metadatenschemata ermöglicht wird. Das Mappingmodell ist in einen zyklischen Mappingprozess eingebunden, der die Anforderungen an Mappinglösungen in vier aufeinanderfolgende Phasen kategorisiert: mapping discovery, mapping representation, mapping execution und mapping maintenance. Im Rahmen dieser Dissertation beschäftigen wir uns hauptsächlich mit der Representation-Phase sowie mit der Transformation von Mappingspezifikationen in ausführbare SPARQL-Abfragen. Zur Unterstützung der Discovery-Phase bietet das Mappingmodell eine Schnittstelle zur Einbindung von Schema- oder Ontologymatching-Algorithmen. Für die Maintenance-Phase präsentieren wir ein einfaches, aber seinen Zweck erfüllendes Mapping-Registry Konzept. Auf Basis des Mappingmodells stellen wir eine Web-basierte Mediator-Wrapper Architektur vor, die Domänenexperten die Möglichkeit bietet, SPARQL-Mediationsschnittstellen zu definieren. Die zu integrierenden Datenquellen müssen dafür durch Wrapper-Komponenen gekapselt werden, welche die enthaltenen Metadaten im Web exponieren und SPARQL-Zugriff ermöglichen. Als beipielhafte Wrapper Komponente präsentieren wir den OAI2LOD Server, mit dessen Hilfe Datenquellen eingebunden werden können, die ihre Metadaten über das Open Archives Initative Protocol for Metadata Harvesting (OAI-PMH) exponieren. Im Rahmen einer Fallstudie zeigen wir, wie Mappings in Web-Umgebungen erstellt werden können und wie unsere Mediator-Wrapper Architektur nach wenigen, einfachen Konfigurationsschritten Metadaten aus unterschiedlichen, heterogenen Datenquellen integrieren kann, ohne dass dadurch die Notwendigkeit entsteht, eine Mapping Lösung in einer lokalen Systemumgebung zu installieren.The integration of metadata from distinct, heterogeneous data sources requires metadata interoperability, which is a qualitative property of metadata information objects that is not given by default. The technique of metadata mapping allows domain experts to establish metadata interoperability in a certain integration scenario. Mapping solutions, as a technical manifestation of this technique, are already available for the intensively studied domain of database system interoperability, but they rarely exist for the Web. If we consider the amount of steadily increasing structured metadata and corresponding metadata schemes on the Web, we can observe a clear need for a mapping solution that can operate in a Web-based environment. To achieve that, we first need to build its technical core, which is a mapping model that provides the language primitives to define mapping relationships. Existing Semantic Web languages such as RDFS and OWL define some basic mapping elements (e.g., owl:equivalentProperty, owl:sameAs), but do not address the full spectrum of semantic and structural heterogeneities that can occur among distinct, incompatible metadata information objects. Furthermore, it is still unclear how to process defined mapping relationships during run-time in order to deliver metadata to the client in a uniform way. As the main contribution of this thesis, we present an abstract mapping model, which reflects the mapping problem on a generic level and provides the means for reconciling incompatible metadata. Instance transformation functions and URIs take a central role in that model. The former cover a broad spectrum of possible structural and semantic heterogeneities, while the latter bind the complete mapping model to the architecture of the Word Wide Web. On the concrete, language-specific level we present a binding of the abstract mapping model for the RDF Vocabulary Description Language (RDFS), which allows us to create mapping specifications among incompatible metadata schemes expressed in RDFS. The mapping model is embedded in a cyclic process that categorises the requirements a mapping solution should fulfil into four subsequent phases: mapping discovery, mapping representation, mapping execution, and mapping maintenance. In this thesis, we mainly focus on mapping representation and on the transformation of mapping specifications into executable SPARQL queries. For mapping discovery support, the model provides an interface for plugging-in schema and ontology matching algorithms. For mapping maintenance we introduce the concept of a simple, but effective mapping registry. Based on the mapping model, we propose aWeb-based mediator wrapper-architecture that allows domain experts to set up mediation endpoints that provide a uniform SPARQL query interface to a set of distributed metadata sources. The involved data sources are encapsulated by wrapper components that expose the contained metadata and the schema definitions on the Web and provide a SPARQL query interface to these metadata. In this thesis, we present the OAI2LOD Server, a wrapper component for integrating metadata that are accessible via the Open Archives Initiative Protocol for Metadata Harvesting (OAI-PMH). In a case study, we demonstrate how mappings can be created in aWeb environment and how our mediator wrapper architecture can easily be configured in order to integrate metadata from various heterogeneous data sources without the need to install any mapping solution or metadata integration solution in a local system environment

Stake Shift in Major Cryptocurrencies: An Empirical Study

In the proof-of-stake (PoS) paradigm for maintaining decentralized, permissionless cryptocurrencies, Sybil attacks are prevented by basing the distribution of roles in the protocol execution on the stake distribution recorded in the ledger itself. However, for various reasons this distribution cannot be completely up-to-date, introducing a gap between the present stake distribution, which determines the parties' current incentives, and the one used by the protocol. In this paper, we investigate this issue, and empirically quantify its effects. We survey existing provably secure PoS proposals to observe that the above time gap between the two stake distributions, which we call stake distribution lag, amounts to several days for each of these protocols. Based on this, we investigate the ledgers of four major cryptocurrencies (Bitcoin, Bitcoin Cash, Litecoin and Zcash) and compute the average stake shift (the statistical distance of the two distributions) for each value of stake distribution lag between 1 and 14 days, as well as related statistics. We also empirically quantify the sublinear growth of stake shift with the length of the considered lag interval. Finally, we turn our attention to unusual stake-shift spikes in these currencies: we observe that hard forks trigger major stake shifts and that single real-world actors, mostly exchanges, account for major stake shifts in established cryptocurrency ecosystems.Comment: 20 pages, 8 figures, 2 tables, paper accepted for publication at Financial Cryptography and Data Security 2020 (FC 2020, see https://fc20.ifca.ai

Increasing the Efficiency of Cryptoasset Investigations by Connecting the Cases

Law enforcement agencies are confronted with a rapidly growing number of cryptoasset-related cases, often redundantly investigating the same cases without mutual knowledge or shared insights. In this paper, we explore the hypothesis that recognizing and acting upon connections between these cases can significantly streamline investigative processes. Through an analysis of a dataset comprising 34 cyberfraud and 1793 sextortion spam cases, we discovered that 41% of the cyberfraud and 96.9% of the sextortion spam incidents can be interconnected. We introduce a straightforward yet effective tool, which is integrated into a broader cryptoasset forensics workflow and allows investigators to highlight and share case connections. Our research unequivocally demonstrates that recognizing case connections can lead to remarkable efficiencies, especially when extended across crime areas, international borders, and jurisdictions

Disentangling Decentralized Finance (DeFi) Compositions

We present the first study on compositions of Decentralized Finance (DeFi) protocols, which aim to disrupt traditional finance and offer financial services on top of the distributed ledgers, such as the Ethereum. Starting from a ground-truth of 23 DeFi protocols and 10,663,881 associated accounts, we study the interactions of DeFi protocols and associated smart contracts from a macroscopic perspective. We find that DEX and lending protocols have a high degree centrality, that interactions among protocols primarily occur in a strongly connected component, and that known community detection cannot disentangle DeFi protocols. Therefore, we propose an algorithm for extracting the building blocks and uncovering the compositions of DeFi protocols. We apply the algorithm and conduct an empirical analysis finding that swaps are the most frequent building blocks and that DeFi aggregation protocols utilize functions of many other DeFi protocols. Overall, our results and methods contribute to a better understanding of a new family of financial products and could play an essential role in assessing systemic risks if DeFi continues to proliferate