Palgol: A High-Level DSL for Vertex-Centric Graph Processing with Remote Data Access

Pregel is a popular distributed computing model for dealing with large-scale graphs. However, it can be tricky to implement graph algorithms correctly and efficiently in Pregel's vertex-centric model, especially when the algorithm has multiple computation stages, complicated data dependencies, or even communication over dynamic internal data structures. Some domain-specific languages (DSLs) have been proposed to provide more intuitive ways to implement graph algorithms, but due to the lack of support for remote access --- reading or writing attributes of other vertices through references --- they cannot handle the above mentioned dynamic communication, causing a class of Pregel algorithms with fast convergence impossible to implement. To address this problem, we design and implement Palgol, a more declarative and powerful DSL which supports remote access. In particular, programmers can use a more declarative syntax called chain access to naturally specify dynamic communication as if directly reading data on arbitrary remote vertices. By analyzing the logic patterns of chain access, we provide a novel algorithm for compiling Palgol programs to efficient Pregel code. We demonstrate the power of Palgol by using it to implement several practical Pregel algorithms, and the evaluation result shows that the efficiency of Palgol is comparable with that of hand-written code.Comment: 12 pages, 10 figures, extended version of APLAS 2017 pape

Efficient and Reasonable Object-Oriented Concurrency

Making threaded programs safe and easy to reason about is one of the chief difficulties in modern programming. This work provides an efficient execution model for SCOOP, a concurrency approach that provides not only data race freedom but also pre/postcondition reasoning guarantees between threads. The extensions we propose influence both the underlying semantics to increase the amount of concurrent execution that is possible, exclude certain classes of deadlocks, and enable greater performance. These extensions are used as the basis an efficient runtime and optimization pass that improve performance 15x over a baseline implementation. This new implementation of SCOOP is also 2x faster than other well-known safe concurrent languages. The measurements are based on both coordination-intensive and data-manipulation-intensive benchmarks designed to offer a mixture of workloads.Comment: Proceedings of the 10th Joint Meeting of the European Software Engineering Conference and the ACM SIGSOFT Symposium on the Foundations of Software Engineering (ESEC/FSE '15). ACM, 201

Model Checking Markov Chains with Actions and State Labels

In the past, logics of several kinds have been proposed for reasoning about discrete- or continuous-time Markov chains. Most of these logics rely on either state labels (atomic propositions) or on transition labels (actions). However, in several applications it is useful to reason about both state-properties and action-sequences. For this purpose, we introduce the logic asCSL which provides powerful means to characterize execution paths of Markov chains with actions and state labels. asCSL can be regarded as an extension of the purely state-based logic asCSL (continuous stochastic logic). \ud In asCSL, path properties are characterized by regular expressions over actions and state-formulas. Thus, the truth value of path-formulas does not only depend on the available actions in a given time interval, but also on the validity of certain state formulas in intermediate states.\ud We compare the expressive power of CSL and asCSL and show that even the state-based fragment of asCSL is strictly more expressive than CSL if time intervals starting at zero are employed. Using an automaton-based technique, an asCSL formula and a Markov chain with actions and state labels are combined into a product Markov chain. For time intervals starting at zero we establish a reduction of the model checking problem for asCSL to CSL model checking on this product Markov chain. The usefulness of our approach is illustrated by through an elaborate model of a scalable cellular communication system for which several properties are formalized by means of asCSL-formulas, and checked using the new procedure

A Denotational Semantics for Communicating Unstructured Code

An important property of programming language semantics is that they should be compositional. However, unstructured low-level code contains goto-like commands making it hard to define a semantics that is compositional. In this paper, we follow the ideas of Saabas and Uustalu to structure low-level code. This gives us the possibility to define a compositional denotational semantics based on least fixed points to allow for the use of inductive verification methods. We capture the semantics of communication using finite traces similar to the denotations of CSP. In addition, we examine properties of this semantics and give an example that demonstrates reasoning about communication and jumps. With this semantics, we lay the foundations for a proof calculus that captures both, the semantics of unstructured low-level code and communication.Comment: In Proceedings FESCA 2015, arXiv:1503.0437

Formative exploration of students’ perception about Community Medicine teaching at Mahatma Gandhi Institute of Medical Sciences, Sewagram, India

Objective: The objectives of the present formative research were to explore the medical undergraduates’ study problems and their perceptions about various teaching approaches in currently practiced teaching curriculum of Community Medicine. Material and Methods: The present formative research was undertaken at Dr. Sushila Nayar School of Public Health incorporating Department of Community Medicine, Mahatma Gandhi Institute of Medical Sciences, Sewagram. The respondents were 17 (26.5%) conveniently selected final year exam appearing medical undergraduates from 2004 regular batch of 64 students. A triangulation of qualitative research methods like free listing, pile sort exercise and a Focus Group Discussion (FGD) were used. A two dimensional scaling and hierarchical cluster analysis was completed with the pile sort data. The data was analyzed by using software Anthropac 4.98.1/X software. Results: The medical undergraduates could understand the topics like Integrated Management of Neonatal and Childhood (IMNCI), Primary Health Care (PHC), cold chain system for vaccines, immunization and health education, dietary survey and cluster survey method taught in the community based camp approaches. Students found it difficult to comprehend the core of subject from the scattered lecture series over a long teaching period, especially using lengthy over head projector/liquid crystal display presentations. The major problems encountered in studying the subject of Community Medicine were difficulty in understanding the concepts of biostatistics, confusions due to apparently similar text in National Health Programs and difficulty to recall disease statistics due to vast syllabus. Conclusions: Students perceived the community based camp approach of teaching as a best method to understand the subject, which is an integration of task oriented assignments, integration of social sciences within medical domain and active community involvement. Hence, the community based camp approach can be scaled up as a best Community Medicine teaching approach. The active learning methods could be used to improve the lectures and the clinics which should be more concentrated in final year of teachin

Green Jobs in a Sustainable Food System

The U.S. food sector is among the most productive in the world and is a significant driver of our economy. Yet, it's failing us in major ways -- putting public health, livelihoods and our environment at great risk. Obesity and diabetes rates are rising, communities are plagued by food deserts, and agriculture runoff is the biggest source of pollution in our rivers and lakes.The good news is that communities across the country are addressing this crisis in innovative ways. Through different community-based efforts, local activists and food advocates are finding ways to improve community health and environmental outcomes while creating a more economically equitable food system.It is within this context that this report identifies opportunities to transform jobs in the green economy and enhance environmental and economic equity outcomes in the future. The initial analysis promises opportunities for workers to build long-term skills, and emphasizes the importance of linking local efforts to broader regional and national policy platforms. This multi-level engagement and collaboration will help set in motion the systemic changes needed to create a more sustainable and equitable food system

Managing a portal of digital web resources by content syndication

As users become more accustomed to continuous Internet access, they will have less patience with the offering of disparate resources. A new generation of portals is being designed that aids users in navigating resource space and in processing the data they retrieved. Such portals offer added value by means of content syndication: the effort to have multiple, federated? resources co-operate in order to profit optimally from their synergy. A portal that offers these advantages, however, can only be of lasting value if it is sustainable. We sketch a way to set up and run an organisation that can manage a content syndication portal in a sustainable way.\ud \u

B-LOG: A branch and bound methodology for the parallel execution of logic programs

We propose a computational methodology -"B-LOG"-, which offers the potential for an effective implementation of Logic Programming in a parallel computer. We also propose a weighting scheme to guide the search process through the graph and we apply the concepts of parallel "branch and bound" algorithms in order to perform a "best-first" search using an information theoretic bound. The concept of "session" is used to speed up the search process in a succession of similar queries. Within a session, we strongly modify the bounds in a local database, while bounds kept in a global database are weakly modified to provide a better initial condition for other sessions. We also propose an implementation scheme based on a database machine using "semantic paging", and the "B-LOG processor" based on a scoreboard driven controller

Sustainable Value Proposition Design in a Product-Service System

Many companies have started to add services to their tangible products in order to defend themselves from increased competition from low-cost economies. Research regarding the transition towards product-service systems (PSS) and how the PSS providers' business models are affected exists, but there is a lack of research regarding how the suppliers to the PSS providers are affected by the transition towards PSS. Therefore, this thesis studies the situation for a supplier/partner to an OEM that has changed their business model to a PSS providing one. As the first step in a development of a new business model aims this thesis to provide guidelines for how to set up value propositions suitable for a supplier/partner in this new environment. When technologically complex products, such as aircraft engines, are provided through PSS offerings it is hard to translate customer needs into quality parameters, which makes it hard to sustain the value to customer over time. Therefore, how to keep the value offering sustainable over time is also investigated in this thesis. The aim of this study was to investigate how a sustainable value proposition can be designed for a product and technology supplier/partner to an OEM that offers PSS solutions. The research has been performed through studying relevant literature and collecting empirical data from a case company through semi-structured interviews and a workshop. The case company in this research is Volvo Aero Corporation (VAC). The empirical findings show that VAC wants to offer product-service bundled solution, which fit the whole spectra of PSS value propositions, to their partners/customers. To be able to deliver these different types of product-service bundled solutions different value propositions that suit the different kinds of PSS offerings are needed. Requirements that must be fulfilled to be able to offer and deliver the different types of value propositions exist in terms of securing sufficient information access, aligning the incentives of all actors involved and achieving an internal consensus of what is delivered