On Spatial Conjunction as Second-Order Logic

Spatial conjunction is a powerful construct for reasoning about dynamically allocated data structures, as well as concurrent, distributed and mobile computation. While researchers have identified many uses of spatial conjunction, its precise expressive power compared to traditional logical constructs was not previously known. In this paper we establish the expressive power of spatial conjunction. We construct an embedding from first-order logic with spatial conjunction into second-order logic, and more surprisingly, an embedding from full second order logic into first-order logic with spatial conjunction. These embeddings show that the satisfiability of formulas in first-order logic with spatial conjunction is equivalent to the satisfiability of formulas in second-order logic. These results explain the great expressive power of spatial conjunction and can be used to show that adding unrestricted spatial conjunction to a decidable logic leads to an undecidable logic. As one example, we show that adding unrestricted spatial conjunction to two-variable logic leads to undecidability. On the side of decidability, the embedding into second-order logic immediately implies the decidability of first-order logic with a form of spatial conjunction over trees. The embedding into spatial conjunction also has useful consequences: because a restricted form of spatial conjunction in two-variable logic preserves decidability, we obtain that a correspondingly restricted form of second-order quantification in two-variable logic is decidable. The resulting language generalizes the first-order theory of boolean algebra over sets and is useful in reasoning about the contents of data structures in object-oriented languages.Comment: 16 page

Fixed Points in the Ambient Logic

We present an extension of the ambient logic with fixed points operators in the style of the mu-calculus. We give a simple syntactic condition for the equivalence between minimal and maximal fixpoint formulas and show how to subsume spatial analogues of the usual box and diamond operators

Logics for Unranked Trees: An Overview

Labeled unranked trees are used as a model of XML documents, and logical languages for them have been studied actively over the past several years. Such logics have different purposes: some are better suited for extracting data, some for expressing navigational properties, and some make it easy to relate complex properties of trees to the existence of tree automata for those properties. Furthermore, logics differ significantly in their model-checking properties, their automata models, and their behavior on ordered and unordered trees. In this paper we present a survey of logics for unranked trees

Separability in the Ambient Logic

The \it{Ambient Logic} (AL) has been proposed for expressing properties of process mobility in the calculus of Mobile Ambients (MA), and as a basis for query languages on semistructured data. We study some basic questions concerning the discriminating power of AL, focusing on the equivalence on processes induced by the logic $(=_L>)$. As underlying calculi besides MA we consider a subcalculus in which an image-finiteness condition holds and that we prove to be Turing complete. Synchronous variants of these calculi are studied as well. In these calculi, we provide two operational characterisations of $_=L$: a coinductive one (as a form of bisimilarity) and an inductive one (based on structual properties of processes). After showing $_=L$ to be stricly finer than barbed congruence, we establish axiomatisations of $_=L$ on the subcalculus of MA (both the asynchronous and the synchronous version), enabling us to relate $_=L$ to structural congruence. We also present some (un)decidability results that are related to the above separation properties for AL: the undecidability of $_=L$ on MA and its decidability on the subcalculus.Comment: logical methods in computer science, 44 page

Elimination of spatial connectives in static spatial logics

AbstractThe recent interest for specification on resources yields so-called spatial logics, that is specification languages offering new forms of reasoning: the local reasoning through the separation of the resource space into two disjoint subspaces, and the contextual reasoning through hypothetical extension of the resource space.We consider two resource models and their related logics:•The static ambient model, proposed as an abstraction of semistructured data (Proc. ESOP’01, Lecture Notes in Computer Science, vol. 2028, Springer, Berlin, 2001, pp. 1–22 (invited paper)) with the static ambient logic (SAL) that was proposed as a request language, both obtained by restricting the mobile ambient calculus (Proc. FOSSACS’98, Lecture Notes in Computer Science, vol. 1378, Springer, Berlin, 1998, pp. 140–155) and logic (Proc. POPL’00, ACM Press, New York, 2000, pp. 365–377) to their purely static aspects.•The memory model and the assertion language of separation logic, both defined in Reynolds (Proc. LICS’02, 2002) for the purpose of the axiomatic semantic of imperative programs manipulating pointers.We raise the questions of the expressiveness and the minimality of these logics. Our main contribution is a minimalisation technique we may apply for these two logics. We moreover show some restrictions of this technique for the extension SAL∀ with universal quantification, and we establish the minimality of the adjunct-free fragment (SALint)

Modelling dynamic web data

We introduce Xd¼, a peer-to-peer model for reasoning about the dynamic behaviour of web data. It is based on an idealised model of semistructured data, and an extension of the ¼-calculus with process mobility and with operations for interacting with data. Our model can be used to reason about behaviour found in, for example, dynamic web page programming, applet interaction, and service orchestration. We study behavioural equivalences for Xd¼, motivated by examples

Combining Temporal Logics for Querying XML Documents

Abstract. Close relationships between XML navigation and temporal logics have been discovered recently, in particular between logics LTL and CTL ⋆ and XPath navigation, and between the µ-calculus and navigation based on regular expressions. This opened up the possibility of bringing model-checking techniques into the field of XML, as documents are naturally represented as labeled transition systems. Most known results of this kind, however, are limited to Boolean or unary queries, which are not always sufficient for complex querying tasks. Here we present a technique for combining temporal logics to capture nary XML queries expressible in two yardstick languages: FO and MSO. We show that by adding simple terms to the language, and combining a temporal logic for words together with a temporal logic for unary tree queries, one obtains logics that select arbitrary tuples of elements, and can thus be used as building blocks in complex query languages. We present general results on the expressiveness of such temporal logics, study their model-checking properties, and relate them to some common XML querying tasks.