A Fine-Grained Hierarchy of Hard Problems in the Separated Fragment

Recently, the separated fragment (SF) has been introduced and proved to be decidable. Its defining principle is that universally and existentially quantified variables may not occur together in atoms. The known upper bound on the time required to decide SF's satisfiability problem is formulated in terms of quantifier alternations: Given an SF sentence $\exists \vec{z} \forall \vec{x}_1 \exists \vec{y}_1 \ldots \forall \vec{x}_n \exists \vec{y}_n . \psi$ in which $\psi$ is quantifier free, satisfiability can be decided in nondeterministic $n$-fold exponential time. In the present paper, we conduct a more fine-grained analysis of the complexity of SF-satisfiability. We derive an upper and a lower bound in terms of the degree of interaction of existential variables (short: degree)}---a novel measure of how many separate existential quantifier blocks in a sentence are connected via joint occurrences of variables in atoms. Our main result is the $k$-NEXPTIME-completeness of the satisfiability problem for the set $SF_{\leq k}$ of all SF sentences that have degree $k$ or smaller. Consequently, we show that SF-satisfiability is non-elementary in general, since SF is defined without restrictions on the degree. Beyond trivial lower bounds, nothing has been known about the hardness of SF-satisfiability so far.Comment: Full version of the LICS 2017 extended abstract having the same title, 38 page

Towards automated restructuring of object oriented systems

The work introduces a method for diagnosing design flaws in object oriented systems, and finding meaningful refactorings to remove such flaws. The method is based on pairing up a structural pattern that is considered pathological (e.g. a code smell or anti-pattern) with a so called design context. The design context describes the design semantics associated to the pathological structure, and the desired strategic closure for that fragment. The process is tool supported and largely automated

MULTIHIERARCHICAL DOCUMENTS AND FINE-GRAINED ACCESS CONTROL

This work presents new models and algorithms for creating, modifying, and controlling access to complex text. The digitization of texts opens new opportunities for preservation, access, and analysis, but at the same time raises questions regarding how to represent and collaboratively edit such texts. Two issues of particular interest are modelling the relationships of markup (annotations) in complex texts, and controlling the creation and modification of those texts. This work addresses and connects these issues, with emphasis on data modelling, algorithms, and computational complexity; and contributes new results in these areas of research. Although hierarchical models of text and markup are common, complex texts often exhibit layers of overlapping structure that are best described by multihierarchical markup. We develop a new model of multihierarchical markup, the globally ordered GODDAG, that combines features of both graph- and range-based models of markup, allowing documents to be unambiguously serialized. We describe extensions to the XPath query language to support globally ordered GODDAGs, provide semantics for a set of update operations on this structure, and provide algorithms for converting between two different representations of the globally ordered GODDAG. Managing the collaborative editing of documents can require restricting the types of changes different editors may make, while not altogether restricting their access to the document. Fine-grained access control allows precisely these kinds of restrictions on the operations that a user is or is not permitted to perform on a document. We describe a rule-based model of fine-grained access control for updates of hierarchical documents, and in this context analyze the document generation problem: determining whether a document could have been created without violating a particular access control policy. We show that this problem is undecidable in the general case and provide computational complexity bounds for a number of restricted variants of the problem. Finally, we extend our fine-grained access control model from hierarchical to multihierarchical documents. We provide semantics for fine-grained access control policies that control splice-in, splice-out, and rename operations on globally ordered GODDAGs, and show that the multihierarchical version of the document generation problem remains undecidable

On Generalizing Decidable Standard Prefix Classes of First-Order Logic

Recently, the separated fragment (SF) of first-order logic has been introduced. Its defining principle is that universally and existentially quantified variables may not occur together in atoms. SF properly generalizes both the Bernays-Sch\"onfinkel-Ramsey (BSR) fragment and the relational monadic fragment. In this paper the restrictions on variable occurrences in SF sentences are relaxed such that universally and existentially quantified variables may occur together in the same atom under certain conditions. Still, satisfiability can be decided. This result is established in two ways: firstly, by an effective equivalence-preserving translation into the BSR fragment, and, secondly, by a model-theoretic argument. Slight modifications to the described concepts facilitate the definition of other decidable classes of first-order sentences. The paper presents a second fragment which is novel, has a decidable satisfiability problem, and properly contains the Ackermann fragment and---once more---the relational monadic fragment. The definition is again characterized by restrictions on the occurrences of variables in atoms. More precisely, after certain transformations, Skolemization yields only unary functions and constants, and every atom contains at most one universally quantified variable. An effective satisfiability-preserving translation into the monadic fragment is devised and employed to prove decidability of the associated satisfiability problem.Comment: 34 page

A heuristic-based approach to code-smell detection

Encapsulation and data hiding are central tenets of the object oriented paradigm. Deciding what data and behaviour to form into a class and where to draw the line between its public and private details can make the difference between a class that is an understandable, flexible and reusable abstraction and one which is not. This decision is a difficult one and may easily result in poor encapsulation which can then have serious implications for a number of system qualities. It is often hard to identify such encapsulation problems within large software systems until they cause a maintenance problem (which is usually too late) and attempting to perform such analysis manually can also be tedious and error prone. Two of the common encapsulation problems that can arise as a consequence of this decomposition process are data classes and god classes. Typically, these two problems occur together – data classes are lacking in functionality that has typically been sucked into an over-complicated and domineering god class. This paper describes the architecture of a tool which automatically detects data and god classes that has been developed as a plug-in for the Eclipse IDE. The technique has been evaluated in a controlled study on two large open source systems which compare the tool results to similar work by Marinescu, who employs a metrics-based approach to detecting such features. The study provides some valuable insights into the strengths and weaknesses of the two approache

The Role of Consciousness in Memory

Conscious events interact with memory systems in learning, rehearsal and retrieval (Ebbinghaus 1885/1964; Tulving 1985). Here we present hypotheses that arise from the IDA computional model (Franklin, Kelemen and McCauley 1998; Franklin 2001b) of global workspace theory (Baars 1988, 2002). Our primary tool for this exploration is a flexible cognitive cycle employed by the IDA computational model and hypothesized to be a basic element of human cognitive processing. Since cognitive cycles are hypothesized to occur five to ten times a second and include interaction between conscious contents and several of the memory systems, they provide the means for an exceptionally fine-grained analysis of various cognitive tasks. We apply this tool to the small effect size of subliminal learning compared to supraliminal learning, to process dissociation, to implicit learning, to recognition vs. recall, and to the availability heuristic in recall. The IDA model elucidates the role of consciousness in the updating of perceptual memory, transient episodic memory, and procedural memory. In most cases, memory is hypothesized to interact with conscious events for its normal functioning. The methodology of the paper is unusual in that the hypotheses and explanations presented are derived from an empirically based, but broad and qualitative computational model of human cognition

Supporting user adaptation in adaptive hypermedia applications

A hypermedia application offers its users a lot of freedom to navigate through a large hyperspace. The rich link structure of the hypermedia application can not only cause users to get lost in the hyperspace, but can also lead to comprehension problems because different users may be interested in different pieces of information or a different level of detail or difficulty. Adaptive hypermedia systems (or AHS for short) aim at overcoming these problems by providing adaptive navigation support and adaptive content. The adaptation is based on a user model that represents relevant aspects about the user. At the Eindhoven University of Technology we developed anAHS, named AHA {DC981. To describe its functionality and that of future adaptive systems we also developed a reference model for the architecture of adaptive hypermedia applications, named AHAM (for Adaptive Hypermedia Application Model) {DHW991. In AHAM knowledge is represented through hierarchies of large composite abstract concepts as well as small atomic ones. AHAM also divides the different aspects of an AHS into a domain model (DM). a user model (UM) and an adaptation model (AM). This division provides a clear separation of concerns when developing an adaptive hypermedia application. In this paper, we concentrate on the user modeling aspects of AHAM, but also describe how they relate to the domain model and the adaptation model. Also. we provide a separation between the adaptation rules an author or system designer writes (as part of the adaptation model) and the system's task of executing these rules in the right order. This distinction leads to a simplification of the author's or system designer's task to write adaptation rules. We illustrate authoring and adaptation in by some examples in the AHS AHA

Supporting user adaptation in adaptive hypermedia applications

A hypermedia application offers its users a lot of freedom to navigate through a large hyperspace. The rich link structure of the hypermedia application can not only cause users to get lost in the hyperspace, but can also lead to comprehension problems because different users may be interested in different pieces of information or a different level of detail or difficulty. Adaptive hypermedia systems (or AHS for short) aim at overcoming these problems by providing adaptive navigation support and adaptive content. The adaptation is based on a user model that represents relevant aspects about the user. At the Eindhoven University of Technology we developed anAHS, named AHA {DC981. To describe its functionality and that of future adaptive systems we also developed a reference model for the architecture of adaptive hypermedia applications, named AHAM (for Adaptive Hypermedia Application Model) {DHW991. In AHAM knowledge is represented through hierarchies of large composite abstract concepts as well as small atomic ones. AHAM also divides the different aspects of an AHS into a domain model (DM). a user model (UM) and an adaptation model (AM). This division provides a clear separation of concerns when developing an adaptive hypermedia application. In this paper, we concentrate on the user modeling aspects of AHAM, but also describe how they relate to the domain model and the adaptation model. Also. we provide a separation between the adaptation rules an author or system designer writes (as part of the adaptation model) and the system's task of executing these rules in the right order. This distinction leads to a simplification of the author's or system designer's task to write adaptation rules. We illustrate authoring and adaptation in by some examples in the AHS AHA