Linda Implementations Using Monitors and Message Passing

Linda is a new parallel programming language that is built around an interprocess communication model called generative communication that differs from previous models in specifying that shared data be added in tuple form to an environment called tuple space, where a tuple exists independently until some process chooses to use it. Interesting properties arise from the model, including space and time uncoupling as well as structured naming. We delineate the essential Linda operations, then discuss the properties of generative communication. We are particularly concerned with implementing Linda on top of two traditional parallel programming paradigms - process communication through globally shared memory via monitors, and process communication in local memory architectures through the use of message passing constructs. We discuss monitors and message passing, then follow with a description of the two Linda implementations

HTTP Mailbox - Asynchronous RESTful Communication

We describe HTTP Mailbox, a mechanism to enable RESTful HTTP communication in an asynchronous mode with a full range of HTTP methods otherwise unavailable to standard clients and servers. HTTP Mailbox allows for broadcast and multicast semantics via HTTP. We evaluate a reference implementation using ApacheBench (a server stress testing tool) demonstrating high throughput (on 1,000 concurrent requests) and a systemic error rate of 0.01%. Finally, we demonstrate our HTTP Mailbox implementation in a human assisted web preservation application called "Preserve Me".Comment: 13 pages, 6 figures, 8 code blocks, 3 equations, and 3 table

PROSET — A Language for Prototyping with Sets

We discuss the prototyping language PROSET(Prototyping with Sets) as a language for experimental and evolutionary prototyping, focusing its attention on algorithm design. Some of PROSET’s features include generative communication, flexible exception handling and the integration of persistence. A discussion of some issues pertaining to the compiler and the programming environment conclude the pape

Modeling adaptation with a tuple-based coordination language

In recent years, it has been argued that systems and applications, in order to deal with their increasing complexity, should be able to adapt their behavior according to new requirements or environment conditions. In this paper, we present a preliminary investigation aiming at studying how coordination languages and formal methods can contribute to a better understanding, implementation and usage of the mechanisms and techniques for adaptation currently proposed in the literature. Our study relies on the formal coordination language Klaim as a common framework for modeling some adaptation techniques, namely the MAPE-K loop, aspect- and context-oriented programming

Encrypted Shared Data Spaces

The deployment of Share Data Spaces in open, possibly hostile, environments arises the need of protecting the confidentiality of the data space content. Existing approaches focus on access control mechanisms that protect the data space from untrusted agents. The basic assumption is that the hosts (and their administrators) where the data space is deployed have to be trusted. Encryption schemes can be used to protect the data space content from malicious hosts. However, these schemes do not allow searching on encrypted data. In this paper we present a novel encryption scheme that allows tuple matching on completely encrypted tuples. Since the data space does not need to decrypt tuples to perform the search, tuple confidentiality can be guaranteed even when the data space is deployed on malicious hosts (or an adversary gains access to the host). Our scheme does not require authorised agents to share keys for inserting and retrieving tuples. Each authorised agent can encrypt, decrypt, and search encrypted tuples without having to know other agents’ keys. This is beneficial inasmuch as it simplifies the task of key management. An implementation of an encrypted data space based on this scheme is described and some preliminary performance results are given

Critical Thinking

{Excerpt} Blaise Pascal felt that “Man is obviously made for thinking. Therein lies all his dignity and his merit; and his whole duty is to think as he ought.” A contemporary of René Descartes, Pascal is however best remembered for resisting rationalism, which he thought could not determine major truths: “The heart has its reasons, which reason does not know.” Blaise Pascal and René Descartes are reference points for two major attitudes to conscious representation of the world: although both saw reason as the primary source of knowledge, they disagreed profoundly over the competence of Man—the truth, as always, lies between faith and radical doubt. For sure, pace the propensity of intellectuals to promulgate eternal truths, or at least make a lasting impression, the idea of critical thinking neither begins nor ends with Pascal or Descartes. Socrates set the agenda nearly 2,500 years ago when the “Socratic Method” established the need to seek evidence, analyze basic concepts, scrutinize reasoning and assumptions, and trace the implications not only of what is said but of what is done as well: “Knowledge will not come from teaching but from questioning.” Thereafter, within the overall framework of skepticism, numerous scholars raised awareness of the potential power of reasoning and of the need for that to be systematically cultivated and cross-examined. Critical thinking, by its very nature, demands recognition that all questioning stems from a point of view and occurs within a frame of reference; proceeds from some purpose—presumably, to answer a question or solve a problem; relies on concepts and ideas that rest in turn on assumptions; has an informational base that must be interpreted; and draws on basic inferences to make conclusions that have implications and consequences. To note, each dimension of reasoning is linked simultaneously with the other; problems of thinking in any of them will impact others and should be monitored. Hence, effective, full-spectrum questioning that connects from multiple perspectives must illuminate each element of thought so it may permeate the model