... This paper concerns the problem of interprocedural slicing---generating a slice of an entire program, where the slice crosses the boundaries of procedure calls. To solve this problem, we introduce a new kind of graph to represent programs, called a system dependence graph, which extends previous dependence representations to incorporate collections of procedures (with procedure calls) rather than just monolithic programs. Our main result is an algorithm for interprocedural slicing that uses the new representation. (It should be noted that our work concerns a somewhat restricted kind of slice: Rather than permitting a program to be sliced with respect to program point p and an arbitrary variable, a slice must be taken with respect to a variable that is defined or used at p.) The chief

In this paper we study the space requirement of algorithms that make only one (or a small number of) pass(es) over the input data. We study such algorithms under a model of data streams that we introduce here. We give a number of upper and lower bounds for problems stemming from queryprocessing, invoking in the process tools from the area of communication complexity.

The evaluation of path expression queries on semistructured data in a distributed asynchronous environment is considered. The focus is on the use of local information expressed in the form of path constraints in the optimization of path expression queries. In particular, decidability and complexity results on the implication problem for path constraints are established.

We consider the following problem: given a labelled directed graph G and a regular expression R, find all pairs of nodes connected by a simple path such that the concatenation of the labels along the path satisfies R. The problem is motivated by the observation that many recursive queries in relational databases can be expressed in this form, and by the implementation of a query language, G+ , based on this observation. We show that the problem is in general intractable, but present an algorithm than runs in polynomial time in the size of the graph when the regular expression and the graph are free of conflicts. We also present a class of languages whose expressions can always be evaluated in time polynomial in the size of both the graph and the expression, and characterize syntactically the expressions for such languages. Key words. Labelled directed graphs, NP-completeness, polynomial-time algorithms, regular expressions, simple paths AMS(MOS) subject classifications. 68P, 6...

. Recursive state machines (RSMs) enhance the power of ordinary state machines by allowing vertices to correspond either to ordinary states or to potentially recursive invocations of other state machines. RSMs can model the control flow in sequential imperative programs containing recursive procedure calls. They can be viewed as a visual notation extending Statecharts-like hierarchical state machines, where concurrency is disallowed but recursion is allowed. They are also related to various models of pushdown systems studied in the verification and program analysis communities. After introducing RSMs, we focus on whether state-space analysis can be performed efficiently for RSMs. We consider the two central problems for algorithmic analysis and model checking, namely, reachability (is a target state reachable from initial states) and cycle detection (is there a reachable cycle containing an accepting state). We show that both these problems can be solved in time O(n` 2 ) and space O(n`), where n is the size of the recursive machine and ` is the maximum, over all component state machines, of the minimum of the number of entries and the number of exits of each component. We also study the precise relationship between RSMs and closely related models. 1

Modern search engines answer keyword-based queries extremely efficiently. The impressive speed is due to clever inverted index structures, caching, a domain-independent knowledge of strings, and thousands of machines. Several research efforts have attempted to generalize keyword search to keytree and keygraph searching, because trees and graphs have many applications in next-generation database systems. This paper surveys both algorithms and applications, giving some emphasis to our own work.

We present a novel approach to scalable implementation of type-based flow analysis with polymorphic subtyping. Using a new presentation of polymorphic subtyping with instantiation constraints, we are able to apply context-free language (CFL) reachability techniques to type-based flow analysis. We develop a CFL-based algorithm for computing flow information in time O(n 3 ), where n is the size of the typed program. The algorithm substantially improves upon the best previously known algorithm for flow analysis based on polymorphic subtyping with complexity O(n 8 ). Our technique also yields the first demand-driven algorithm for polymorphic subtype-based flow-computation. It works directly on higher-order programs with structured data of finite type (unbounded data structures are incorporated via finite approximations), supports context-sensitive, global flow summarization and includes polymorphic recursion.

We present an algorithm for verifying that a model M with timing constraints satisfies a given temporal property T . The model M is given as a parallel composition of !-automata P i , where each automaton P i is constrained by bounds on delays. The property T is given as an !-automaton as well, and the verification problem is posed as a language inclusion question L(M ) ` L(T ). In constructing the composition M of the constrained automata P i , one needs to rule out the behaviors that are inconsistent with the delay bounds, and this step is (provably) computationally expensive. We propose an iterative solution which involves generating successive approximations M j to M , with containment L(M ) ` L(M j ) and monotone convergence L(M j ) ! L(M ) within a bounded number of steps. As the succession progresses, the approximations M j become more complex. At any step of the iteration one may get a proof or a counterexample to the original language inclusion question. The described algori...

. Hierarchical State Machines (HSMs) are a natural model for representing the behavior of software systems. In this paper, we investigate a variety of model-checking problems for an extension of HSMs in which state machines are allowed to call each other recursively. 1

Abstract. This paper studies the RDF model from a database perspective. From this point of view it is compared with other database models, particularly with graph database models, which are very close in motivations and use cases to RDF. We concentrate on query languages, analyze current RDF trends, and propose the incorporation to RDF query languages of primitives which are not present today, based on the experience and techniques of graph database research. 1