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The results of three piloted simulations investigating flight-deck surface trajectory-based operations (STBO) are presented. Commercial transport pilots were given taxi clearances with time and speed components on the primary flight display and were required to taxi to the departing runway or intermediate intersections. Results show that when pilots were provided with speed-only taxi clearances, pilots either had poor required time of arrival (RTA) conformance with acceptable estimates of attentional distribution and safety, or had good RTA conformance with unacceptable attentional distribution and safety estimates. A flight-deck error-nulling algorithm/display allowed pilots to conform accurately with taxi RTA clearances while maintaining safety. Results are discussed in terms of pilot multitasking in the busy airport surface operations environment. [ABSTRACT FROM PUBLISHER]

In practice, any database management system sometimes needs reorganization, that is, a change in some aspect of the logical and/or physical arrangement of a database. In traditional practice, many types of reorganization have required denying access to a database (taking the database offline) during reorganization. Taking a database offline can be unacceptable for a highly available (24-hour) database, for example, a database serving electronic commerce or armed forces, or for a very large database. A solution is to reorganize online (concurrently with usage of the database, incrementally during users' activities, or interpretively). This article is a tutorial and survey on requirements, issues, and strategies for online reorganization. It analyzes the issues and then presents the strategies, which use the issues. The issues, most of which involve design trade-offs, include use of partitions, the locus of control for the process that reorganizes (a background process or users' activities), reorganization by copying to newly allocated storage (as opposed to reorganizing in place), use of differential files, references to data that has moved, performance, and activation of reorganization. The article surveys online strategies in three categories of reorganization. The first category, maintenance, involves restoring the physical arrangement of data instances without changing the database definition. This category includes restoration of clustering, reorganization of an index, rebalancing of parallel or distributed data, garbage collection for persistent storage, and cleaning (reclamation of space) in a logstructured file system. The second category involves changing the physical database definition; topics include construction of indexes, conversion between B+-trees and linear hash files, and redefinition (e.g., splitting) of partitions. The third category involves changing the logical database definition. Some examples are changing a column's data type, changing the inheritance hierarchy of object classes, and changing a relationship from one-to-many to many-to-many. The survey encompasses both research and commercial implementations, and this article points out several open research topics. As highly available or very large databases continue to become more common and more important in the world economy, the importance of online reorganization is likely to continue growing. [ABSTRACT FROM AUTHOR]

Predicate dispatch is an object-oriented (OO) language mechanism for determining the method implementation to be invoked upon a message send. With predicate dispatch, each method implementation includes a predicate guard specifying the conditions under which the method should be invoked, and logical implication of predicates determines the method overriding relation. Predicate dispatch naturally unifies and generalizes several common forms of dynamic dispatch, including traditional OO dispatch, multimethod dispatch, and functional-style pattern matching. Unfortunately, prior languages supporting predicate dispatch have had several deficiencies that limit the practical utility of this language feature. We describe JPred, a backward-compatible extension to Java supporting predicate dispatch. While prior languages with predicate dispatch have been extensions to toy or nonmainstream languages, we show how predicate dispatch can be naturally added to a traditional OO language. While prior languages with predicate dispatch have required the whole program to be available for typechecking and compilation, JPred retains Java's modular typechecking and compilation strategies. While prior languages with predicate dispatch have included special-purpose algorithms for reasoning about predicates, JPred employs general-purpose, off-the-shelf decision procedures. As a result, JPred's type system is more flexible, allowing several useful programming idioms that are spuriously rejected by those other languages. After describing the JPred language informally, we present an extension to Featherweight Java that formalizes the language and its modular type system, which we have proven sound. Finally, we discuss two case studies that illustrate the practical utility of JPred, including its use in the detection of several errors. [ABSTRACT FROM AUTHOR]

Programs are increasingly organized around features, which are encapsulated using aspects and other linguistic mechanisms. Despite their growing popularity amongst developers, there is a dearth of techniques for computer-aided verification of programs that employ these mechanisms. We present the theoretical underpinnings for applying model checking to programs (expressed as state machines) written using these mechanisms. The analysis is incremental, examining only components that change rather than verifying the entire system every time one part of it changes. Our technique assumes that the set of pointcut designators is known statically, but the actual advice can vary. It handles both static and dynamic pointcut designators. We present the algorithm, prove it sound, and address several subtleties that arise, including cascading advice application and problems of circular reasoning. [ABSTRACT FROM AUTHOR]