In previous work, we introduced scope graphs as a formalism for describing program binding structure and performing name resolution in an AST-independent way. In this paper, we show how to use scope graphs to build static semantic analyzers. We use constraints extracted from the AST to specify facts about binding, typing, and initialization. We treat name and type resolution as separate building blocks, but our approach can handle language constructs-such as record field access-for which binding and typing are mutually dependent. We also refine and extend our previous scope graph theory to address practical concerns including ambiguity checking and support for a wider range of scope relationships. We describe the details of constraint generation for a model language that illustrates many of the interesting static analysis issues associated with modules and records.

Scope graphs are a promising generic framework to model the binding structures of programming languages, bridging formalization and implementation, supporting the definition of type checkers and the automation of type safety proofs. However, previous work on scope graphs has been limited to simple, nominal type systems. In this paper, we show that viewing scopes as types enables us to model the internal structure of types in a range of non-simple type systems (including structural records and generic classes) using the generic representation of scopes. Further, we show that relations between such types can be expressed in terms of generalized scope graph queries. We extend scope graphs with scoped relations and queries. We introduce Statix, a new domain-specific metalanguage for the specification of static semantics, based on scope graphs and constraints. We evaluate the scopes as types approach and the Statix design in case studies of the simply-typed lambda calculus with records, System F, and Featherweight Generic Java.

There is a large gap between the specification of type systems and the implementation of their type checkers, which impedes reasoning about the soundness of the type checker with respect to the specification. A vision to close this gap is to automatically obtain type checkers from declarative programming language specifications. This moves the burden of proving correctness from a case-by-case basis for concrete languages to a single correctness proof for the specification language. This vision is obstructed by an aspect common to all programming languages: name resolution. Naming and scoping are pervasive and complex aspects of the static semantics of programming languages. Implementations of type checkers for languages with name binding features such as modules, imports, classes, and inheritance interleave collection of binding information (i.e., declarations, scoping structure, and imports) and querying that information. This requires scheduling those two aspects in such a way that query answers are stableÐi.e., they are computed only after all relevant binding structure has been collected. Type checkers for concrete languages accomplish stability using language-specific knowledge about the type system.In this paper we give a language-independent characterization of necessary and sufficient conditions to guarantee stability of name and type queries during type checking in terms of critical edges in an incomplete scope graph. We use critical edges to give a formal small-step operational semantics to a declarative specification language for type systems, that achieves soundness by delaying queries that may depend on missing information. This yields type checkers for the specified languages that are sound by constructionÐi.e., they schedule queries so that the answers are stable, and only accept programs that are name-and type-correct according to the declarative language specification. We implement this approach, and evaluate it against specifications of a small module and record language, as well as subsets of Java and Scala.CCS Concepts: • Theory of computation → Constraint and logic programming; Operational semantics.

In this paper, we present various challenges that arise in the delivery and exchange of multimedia information to mobile devices. Specifically, we focus on techniques for maintaining QoS to end-user multimedia applications (e.g. video streaming, multimedia conferencing) while maximizing device lifetimes. In order to cope with the resource intensive nature of multimedia applications (in terms of computation, bandwidth and consequently power) and dynamic congestion levels in wireless networks, an end-to-end approach to QoSaware power optimization is required. We discuss the trend towards such an integrated approach that couples the architectural, OS, middleware and application layers to achieve both user experience and device energy gains. We conclude with a discussion of tools for integrated system design and testing that will aid in rapid deployment of wireless multimedia. MotivationLimiting the energy consumption of low-power mobile devices has become an important research objective in recent years. The capabilities of these devices are limited by their modest sizes and the finite lifetimes of the batteries that power them. As a result, minimizing the energy usage of every component (e.g. CPU, network card, display, architecture etc.) in such devices remains an important design goal and continues to pose significant challenges. On the other hand, rapid advances in processor and wireless networking technology are ushering in a new class of multimedia applications (e.g. video streaming/conferencing) for mobile handheld devices. Multimedia applications have distinctive Quality of Service(QoS) and processing requirements which tend to make them extremely resource-hungry. Moreover, the device specific attributes(e.g form factorof handhelds) significantly influence the human perception of multimedia quality. As a result delivering high quality realtime multimedia content to mobile handheld devices remains a difficult challenge.These issues have been aggressively pursued by researchers and numerous interesting power optimization solutions have been proposed at various cross computational levels -system cache and external memory access optimizations [2,11], dynamic voltage scaling(DVS) [18,6] of the CPU, dynamic power management of disks and network interfaces(NICs) [7,

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