arXiv subjects

Ana Oliveira da Costa

Publications and source records attributed to Ana Oliveira da Costa.

7 recordsLinked to original sources

arXiv2026

TL;QR: Querying Temporal Discursive Patterns in Textual Corpora

Many questions about large textual corpora concern patterns that unfold over time, such as a political group whose stance on a topic drifts from support to criticism over several years of debates. We present TL;QR (Too Long; Query with logical temporal Reasoning), a declarative query language and open-source engine for finding such temporal discursive patterns. In TL;QR, a single query combines natural-language predicates, whose truth is judged by a Large Language Model (LLM), with regular expressions and the operators of a temporal logic. The LLM answers only local questions about individual text passages; a symbolic engine then aggregates these judgments over time and links every match to the recorded passages and predicate decisions behind it. With this division of labor, the temporal and relational reasoning stays exact and auditable even over long time horizons. In addition, when a query includes a regular-expression pre-filter, only a small fraction of the corpus ever reaches the LLM. On a suite of controlled synthetic benchmarks with temporally and semantically complex patterns, TL;QR is substantially more accurate than LLM-only baselines. In a case study on ten years of European Parliament debates (442,593 multilingual speeches), TL;QR identifies candidate shifts in the political groups' stances on the GDPR privacy regulation.

cs.CL↗

arXiv2026

Monitoring Hyperproperties over Observed and Constructed Traces

Hyperproperties specify system requirements that relate multiple executions. Reasoning about such properties naturally involves executions that play different roles: some correspond to concrete behaviors of the system under verification, while others represent idealized or alternative executions defined by the specification. We propose a framework that makes this semantic distinction explicit by distinguishing between observed and constructed traces. Constructed traces are built using generators: functions provided at specification time and invoked by monitors at runtime. Our main motivation lies in the runtime verification of hyperproperties, where only a finite view on possible executions is available. Our approach enables sound runtime verification for a broader class of hyperproperties than approaches that do not account for constructed traces, including properties with quantifier alternation, such as opacity in security, and properties defined with respect to idealized executions, such as linearizability in concurrency. We present a monitoring algorithm incorporating generator-constructed traces, and evaluate it on hyperproperties ranging from security to concurrency, demonstrating that constructed traces not only broaden expressivity but can also significantly accelerate violation detection.

cs.LO↗

arXiv2025

Flavors of Quantifiers in Hyperlogics

Hypertrace logic is a sorted first-order logic with separate sorts for time and execution traces. Its formulas specify hyperproperties, which are properties relating multiple traces. In this work, we extend hypertrace logic by introducing trace quantifiers that range over the set of all possible traces. In this extended logic, formulas can quantify over two kinds of trace variables: constrained trace variables, which range over a fixed set of traces defined by the model, and unconstrained trace variables, which can be assigned to any trace. In comparison, hyperlogics such as HyperLTL have only constrained trace quantifiers. We use hypertrace logic to study how different quantifier patterns affect the decidability of the satisfiability problem. We prove that hypertrace logic without constrained trace quantifiers is equivalent to monadic second-order logic of one successor (S1S), and therefore satisfiable, and that the trace-prefixed fragment (all trace quantifiers precede all time quantifiers) is equivalent to HyperQPTL. Moreover, we show that all hypertrace formulas where the only alternation between constrained trace quantifiers is from an existential to a universal quantifier are equisatisfiable to formulas without constraints on their trace variables and, therefore, decidable as well. Our framework allows us to study also time-prefixed hyperlogics, for which we provide new decidability and undecidability results

cs.LO↗

arXiv2024

Information-flow Interfaces and Security Lattices

Information-flow interfaces is a formalism recently proposed for specifying, composing, and refining system-wide security requirements. In this work, we show how the widely used concept of security lattices provides a natural semantic interpretation for information-flow interfaces.

cs.FL↗

arXiv2024

Hypernode Automata

We introduce hypernode automata as a new specification formalism for hyperproperties of concurrent systems. They are finite automata with nodes labeled with hypernode logic formulas and transitions labeled with actions. A hypernode logic formula specifies relations between sequences of variable values in different system executions. Unlike HyperLTL, hypernode logic takes an asynchronous view on execution traces by constraining the values and the order of value changes of each variable without correlating the timing of the changes. Different execution traces are synchronized solely through the transitions of hypernode automata. Hypernode automata naturally combine asynchronicity at the node level with synchronicity at the transition level. We show that the model-checking problem for hypernode automata is decidable over action-labeled Kripke structures, whose actions induce transitions of the specification automaton. For this reason, hypernode automaton is a suitable formalism for specifying and verifying asynchronous hyperproperties, such as declassifying observational determinism in multi-threaded programs.

cs.FL↗

arXiv2021

Flavours of Sequential Information Flow

Information-flow policies prescribe which information is available to a given user or subsystem. We study the problem of specifying such properties in reactive systems, which may require dynamic changes in information-flow restrictions between their states. We formalize several flavours of sequential information-flow, which cover different assumptions about the semantic relation between multiple observations of a system. Information-flow specification falls into the category of hyperproperties. We define different variants of sequential information-flow specification using a first-order logic with both trace quantifiers and temporal quantifiers called Hypertrace Logic. We prove that HyperLTL, equivalent to a subset of Hypertrace Logic with restricted quantifier prefixes, cannot specify the majority of the studied two-state independence variants. For our results, we introduce a notion of equivalence between sets of traces that cannot be distinguished by certain classes of formulas in Hypertrace Logic. This presents a new approach to proving inexpressiveness results for logics such as HyperLTL.

cs.LO↗

arXiv2020

Information-Flow Interfaces

Contract-based design is a promising methodology for taming the complexity of developing sophisticated systems. A formal contract distinguishes between assumptions, which are constraints that the designer of a component puts on the environments in which the component can be used safely, and guarantees, which are promises that the designer asks from the team that implements the component. A theory of formal contracts can be formalized as an interface theory, which supports the composition and refinement of both assumptions and guarantees. Although there is a rich landscape of contract-based design methods that address functional and extra-functional properties, we present the first interface theory that is designed for ensuring system-wide security properties, thus paving the way for a science of safety and security co-engineering. Our framework provides a refinement relation and a composition operation that support both incremental design and independent implementability. We develop our theory for both stateless and stateful interfaces. We illustrate the applicability of our framework with an example inspired from the automotive domain. Finally, we provide three plausible trace semantics to stateful information-flow interfaces and we show that only two correspond to temporal logics for specifying hyperproperties, while the third defines a new class of hyperproperties that lies between the other two classes.

cs.FL↗