Transducer-Based Rewriting Games for Active XML

Context-free games are two-player rewriting games that are played on nested strings representing XML documents with embedded function symbols. These games were introduced to model rewriting processes for intensional documents in the Active XML framework, where input documents are to be rewritten into a given target schema by calls to external services. This paper studies the setting where dependencies between inputs and outputs of service calls are modelled by transducers, which has not been examined previously. It defines transducer models operating on nested words and studies their properties, as well as the computational complexity of the winning problem for transducer-based context-free games in several scenarios. While the complexity of this problem is quite high in most settings (ranging from NP-complete to undecidable), some tractable restrictions are also identified.Comment: Extended version of MFCS 2016 conference pape

Which DTDs are streaming bounded repairable?

ABSTRACT Integrity constraint management concerns both checking whether data is valid and taking action to restore correctness when invalid data is discovered. In XML the notion of valid data can be captured by schema languages such as Document Type Definitions (DTDs) and more generally XML schemas. DTDs have the property that constraint checking can be done in streaming fashion. In this paper we consider when the corresponding action to restore validity -repair -can be done in streaming fashion. We formalize this as the problem of determining, given a DTD, whether or not a streaming procedure exists that transforms an input document so as to satisfy the DTD, using a number of edits independent of the document. We show that this problem is decidable. In fact, we show the decidability of a more general problem, allowing a more general class of schemas than DTDs, and requiring a repair procedure that works only for documents that are already known to satisfy another class of constraints. The decision procedure relies on a new analysis of the structure of DTDs, reducing to a novel notion of game played on pushdown systems associated with the schemas

Valorant and the Platformization of Free-To-Play Games

By studying the early development stages of the free-to-play game Valorant (Riot Games, 2020), this research draws connections between game studies and recent platformization research. Traditionally, game scholars have treated the game industry as focused on selling premium-priced games. An alternative approach presents games as services that attempt to foster a long-term relationship with the player base. This paper zooms in on the latter, by studying the role of livestreaming in the service model of digital games. This sheds light on how service games can become intertwined with participatory modes of production, which benefits the longevity of service games. It points to a situation in which games, users, and platforms together make up one coherent system. The deployment of sociotechnical system scholarship identifies mechanisms that have been put in place to facilitate the interaction between users and platforms. With that in mind, this paper presents a qualitative content analysis of Twitch streams using a transcription method in which content creation is considered vital to the proliferation of the platform ecosystem. This work contributes to a growing body of literature bridging the fields of platform studies and game studies by taking into account the extended cultural practices and paratexts of both livestreaming and videogames

Logic Programming Applications: What Are the Abstractions and Implementations?

This article presents an overview of applications of logic programming, classifying them based on the abstractions and implementations of logic languages that support the applications. The three key abstractions are join, recursion, and constraint. Their essential implementations are for-loops, fixed points, and backtracking, respectively. The corresponding kinds of applications are database queries, inductive analysis, and combinatorial search, respectively. We also discuss language extensions and programming paradigms, summarize example application problems by application areas, and touch on example systems that support variants of the abstractions with different implementations

Context-free games on strings and nested words

Kontextfreie Spiele sind ein formales Modell, welches in seiner einfachsten Form den Ableitungsmechanismus kontextfreier Grammatiken zu einem Spiel für zwei Spieler (genannt Juliet und Romeo) verallgemeinert; dabei wählt in einer gegebenen Satzform (d.h. einer Zeichenkette aus Terminal- und Nichtterminalsymbolen) jeweils Juliet ein zu ersetzendes Nichtterminalsymbol aus, worauf Romeo jeweils entsprechend den Ableitungsregeln entscheidet, wodurch dieses Nichtterminalsymbol ersetzt werden soll. Die Gewinnbedingung für Juliet in einem solchen Spiel ist das Erreichen einer Satzform aus einer gegebenen Zielsprache, wohingegen Romeo die Aufgabe hat, dies zu verhindern. Das zentrale algorithmische Problem in kontextfreien Spielen stellt die Frage, gegeben ein Spiel und eine initiale Satzform, ob Juliet in dem gegebenen Spiel auf der Satzform eine Gewinnstrategie hat. Die zentrale praktische Anwendung kontextfreier Spiele liegt in der Modellierung von Active XML-Dokumenten, d.h. XML-Dokumenten, die Referenzen auf externe Quellen enthalten, welche zur Laufzeit aufgerufen werden können um aktuelle Daten in das Dokument einzufügen. Vor diesem Hintergrund ist es sinnvoll, Erweiterungen der oben genannten kontextfreien Spiele auf verschachtelte Wörter zu betrachten, also auf XML-artige Linearisierungen von Bäumen in Zeichenketten. Weitere praktisch motivierte Verallgemeinerungen beinhalten unter anderem die Modellierung von syntaktischer oder semantischer Behandlung von Aufrufparametern beim Aufruf externer Referenzen. Ziel dieser Dissertation ist, einen weitgehend vollständigen Überblick über den aktuellen Stand der Forschung zu kontextfreien Spielen auf Zeichenketten und verschachtelten Wörtern zu liefern. Dazu liefert sie jeweils komplexitätstheoretische Klassifizierungen des Gewinnproblems (und verwandter Probleme) für diverse Varianten kontextfreie Spiele auf Zeichenketten und verschachtelten Wörtern und gibt einen Überblick über Beweismethoden und algorithmische Techniken zur Behandlung dieses Gewinnproblems. Als Teil dieser Betrachtung stellt sie darüber hinaus grundlegende Ergebnisse zu relevanten Automatenmodellen auf verschachtelten Wörtern dar, darunter Varianten von alternierenden Automaten und Transducern

Trading Performance for Stability in Markov Decision Processes

We study the complexity of central controller synthesis problems for finite-state Markov decision processes, where the objective is to optimize both the expected mean-payoff performance of the system and its stability. We argue that the basic theoretical notion of expressing the stability in terms of the variance of the mean-payoff (called global variance in our paper) is not always sufficient, since it ignores possible instabilities on respective runs. For this reason we propose alernative definitions of stability, which we call local and hybrid variance, and which express how rewards on each run deviate from the run's own mean-payoff and from the expected mean-payoff, respectively. We show that a strategy ensuring both the expected mean-payoff and the variance below given bounds requires randomization and memory, under all the above semantics of variance. We then look at the problem of determining whether there is a such a strategy. For the global variance, we show that the problem is in PSPACE, and that the answer can be approximated in pseudo-polynomial time. For the hybrid variance, the analogous decision problem is in NP, and a polynomial-time approximating algorithm also exists. For local variance, we show that the decision problem is in NP. Since the overall performance can be traded for stability (and vice versa), we also present algorithms for approximating the associated Pareto curve in all the three cases. Finally, we study a special case of the decision problems, where we require a given expected mean-payoff together with zero variance. Here we show that the problems can be all solved in polynomial time.Comment: Extended version of a paper presented at LICS 201

Customer engagement through gamification marketing in China: a focus on the luxury market.

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Communities in (Digital) Space: Creating Networks for Daily Living Through Pervasive Media

Studies of online communities often focus either on communities that produce texts or the texts with which individuals engage. This dissertation examines online communities that practice in ongoing activities, in their leisure time, often with no end goal of producing any final text. Through interviews, surveys, and community forum analysis of running, gaming, and translation communities, this study finds that place and everyday habits factor heavily into the ways that sustained online communities structure their work. “Place” can have several meanings within this context, including the communities valuing specific locations or working with specific individuals because of where they live. Due to the rise in use of pervasive mobile devices, online community access often weaves into members’ offline lives. This knowledge of life ancillary to online community adds a layer of affective work to online community participation. Throughout the data collected from these communities, stories pertaining to the work of community maintenance dominated the conversation. Participants defined “work” as managing community involvement around other obligations, maintaining relationships across distances, and acknowledging the benefits that corporate entities derive from these communities. By investigating work within this context, we expand our understanding of the ways less visible populations work online in their leisure time