On rigorous transaction scheduling

The class of transaction scheduling mechanisms in which the transaction serialization order can be determined by controlling their commitment order, is defined. This class of transaction management mechanisms is important, because it simplifies transaction management in a multidatabase system environment. The notion of analogous execution and serialization orders of transactions is defined and the concept of strongly recoverable and rigorous execution schedules is introduced. It is then proven that rigorous schedulers always produce analogous execution and serialization orders. It is shown that the systems using the rigorous scheduling can be naturally incorporated in hierarchical transaction management mechanisms. It is proven that several previously proposed multidatabase transaction management mechanisms guarantee global serializability only if all participating databases systems produce rigorous schedules     

Null values in nested relational databases

Summary The desire to extend the applicability of the relational model beyond traditional data-processing applications has stimulated interest in nested or non-first normal form relations in which the attributes of a relation can take on values which are sets or even relations themselves. In this paper, we study the role of null values in the nested relational model using an open world assumption. We extend the traditional theory and study the properties of extended operators for nested relations containing nulls. The no-information, unknown, and non-existent interpretation of nulls are discussed and the meaning of empty set is clarified. Finally, contrary to several previous results, we determine that the traditional axiomatization of functional and multivalued dependencies is valid in the presence of nulls.Currently with the Air Force Institute of Technology, AFIT/ENG, Wright-Patterson AFB, OH 45433, USAResearch partially supported by an IBM Faculty Development A ward and NSF grant DCR-8507224     

Distributed Multi-Level Recovery in Main-Memory Databases

In this paper we present recovery techniques for distributed main-memory databases, specifically for client-server and shared-disk architectures. We present a recovery scheme for client-server architectures which is based on shipping log records to the server, and two recovery schemes for shared-disk architectures—one based on page shipping, and the other based on broadcasting of the log of updates. The schemes offer different tradeoffs, based on factors such as update rates.Our techniques are extensions to a distributed-memory setting of a centralized recovery scheme for main-memory databases, which has been implemented in the Dalì main-memory database system. Our centralized as well as distributed-memory recovery schemes have several attractive features—they support an explicit multi-level recovery abstraction for high concurrency, reduce disk I/O by writing only redo log records to disk during normal processing, and use per-transaction redo and undo logs to reduce contention on the system log. Further, the techniques use a fuzzy checkpointing scheme that writes only dirty pages to disk, yet minimally interferes with normal processing—all but one of our recovery schemes do not require updaters to even acquire a latch before updating a page. Our log shipping/broadcasting schemes also support concurrent updates to the same page at different sites.     

On periodic resource scheduling for continuous-media databases

The Enhanced Pay-Per-View (EPPV) model for providing continuous-media services associates with each continuous-media clip a display frequency that depends on the clip's popularity. The aim is to increase the number of clients that can be serviced concurrently beyond the capacity limitations of available resources, while guaranteeing a constraint on the response time. This is achieved by sharing periodic continuous-media streams among multiple clients. The EPPV model offers a number of advantages over other data-sharing schemes (e.g., batching), which make it more attractive to large-scale service providers. In this paper, we provide a comprehensive study of the resource-scheduling problems associated with supporting EPPV for continuous-media clips with (possibly) different display rates, frequencies, and lengths. Our main objective is to maximize the amount of disk bandwidth that is effectively scheduled under the given data layout and storage constraints. Our formulation gives rise to -hard combinatorial optimization problems that fall within the realm of hard real-time scheduling theory. Given the intractability of the problems, we propose novel heuristic solutions with polynomial-time complexity. We also present preliminary experimental results for the average case behavior of the proposed scheduling schemes and examine how they compare to each other under different workloads. A major contribution of our work is the introduction of a robust scheduling framework that, we believe, can provide solutions for a variety of realistic EPPV resource-scheduling scenarios, as well as any scheduling problem involving regular, periodic use of a shared resource. Based on this framework, we propose various interesting research directions for extending the results presented in this paper. Received June 9, 1998 / Accepted October 13, 1998     

Similarities and differences in four views of David.

In this article, each author gives a brief comment on similarities he or she sees throughout the case formulations captured in the articles by Watson (2010a), Silberschatz (2010), Goldfried (2010), and Caspar (2010). A systematic comparison is added. Overall, the impression is confirmed and maintained that if authors are ready to renounce the use of the jargon of their specific approach, many similarities can be found. There are nevertheless differences that would lead us to expect a different course of therapy and different effects beyond the main effect of recovery in the case of David, pursuing the conceptualization and interventions proposed by Watson (2010b). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Are results of randomized controlled trials useful to psychotherapists?

Two clinicians provided opposite answers to the title question: Persons argued that information from randomized controlled trials (RCTs) is vital to clinicians, and Silberschatz argued that information from RCTs is irrelevant to clinicians. Persons argued that clinicians cannot provide top quality care to their patients without attending to findings of RCTs and that clinicians have an ethical responsibility to inform patients about, recommend, and provide treatments supported by RCTs before informing patients about, recommending, and providing treatments shown to be inferior in RCTs or not evaluated in RCTs. Silberschatz argued that RCTs do not and cannot answer questions that concern practicing clinicians. He advocates alternative research approaches (effectiveness studies, quasi-experimental methods, case-specific research) for studying psychotherapy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

On the access-control mechanism of the program component manager

This paper examines various issues that pertain to the access-control mechanism of the program component manager. We examine such questions as what constitutes an access-right, what kind of information about managed resources does one need, how revocation keys, right-sets, and exception conditions are handled, etc. It is argued that most of these issues can be handled by the compiler with no explicit programming required. This simplifies the task of programming and enhances reliability. A possible method for handling these issues which was adopted in our implementation is also described.     

How patients coach their therapists in psychotherapy.

Examines coaching behavior in the therapeutic relationship from the perspective of control mastery theory. The expanded concept of coaching presented here views the patient as actively engaged throughout therapy in prompting, instructing, and educating the therapist to relevant aspects of the patient's plan for disconfirming pathogenic beliefs and attaining treatment goals. Three therapy situations encountered when coaching is prominent are identified and illustrated with clinical vignettes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Clinical implications of research on brief dynamic psychotherapy II. How the therapist helps or hinders therapeutic progress.

In this second of a two-part article, we describe how the therapist's interpretations promote therapeutic progress. Any therapist behavior that is in accord with the patient's plan will be helpful to the patient, but interventions that are at cross purposes with the patient's plan will not be helpful. The implications of the plan concept for brief dynamic therapy are described and contrasted with other key technical, concepts such as transference interpretations, therapeutic alliance, and interpretive activity. The importance of understanding the patient's plan and intervening in accord with it are illustrated in several case vignettes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mapping Datalog program execution to networks of processors

The problem of mapping the parallel bottom up execution of Datalog programs to an interconnected network of processors is studied. The parallelization is achieved by using hash functions that partition the set of instantiations for the rules. We first examine this problem in an environment where the number of processors and the interconnection topology is known, and communication between program segments residing at non-adjacent processors is not permitted. An algorithm is presented that decides whether a given Datalog program can be mapped onto such an architecture. We then relax the constraint on the architecture by allowing program segments residing at non-adjacent processors to communicate, A theory of approximate mappings is developed, and an algorithm to obtain the closest approximate mapping of a given Datalog program onto a given architecture is presented