Pointcuts, advice, refinements, and collaborations: similarities, differences, and synergies

Aspect-oriented programming (AOP) is a novel programming paradigm that aims at modularizing complex software. It embraces several mechanisms including (1) pointcuts and advice as well as (2) refinements and collaborations. Though all these mechanisms deal with crosscutting concerns, i.e., a special class of design and implementation problems that challenge traditional programming paradigms, they do so in different ways. In this article we explore their relationship and their impact on modularity, which is an important prerequisite for reliable and maintainable software. Our exploration helps researchers and practitioners to understand their differences and exposes which mechanism is best used for which problem.     

Household technology adoption,use, and impacts: Past,present, and future

Since the 1980s, researchers have been studying the phenomenon associated with technology being diffused to the household. In this paper, three themes in that stream of research, specifically adoption, use, and impacts, are explored. Key studies from prior research within each theme are discussed and directions for future research are offered. The directions for future research range from investigating adoption issues associated with the digital divide to understanding the impacts of new technology and social networking sites on individuals and families. The evolving nature of the technology continues to offer interesting research directions and challenges, with the study of unintended consequences of technology use presenting, perhaps, the greatest opportunities.

Information and communication activity,its essence,structure, and types

The problem of defining the primary forms of information objects is considered. It is proposed to include messages, algorithms, and models in this class.     

Petri nets, algebras, morphisms, and compositionality

It is shown how a category of Petri nets can be viewed as a subcategory of two sorted algebras over multisets. This casts Petri nets in a familiar framework and provides a useful idea of morphism on nets different from the conventional definition—the morphisms here respect the behaviour of nets. The categorical constructions which result provide a useful way to synthesise nets and reason about nets in terms of their components; for example, various forms of parallel composition of Petri nets arise naturally from the product in the category. This abstract setting makes plain a useful functor from the category of Petri nets to a category of spaces of invariants and provides insight into the generalisations of the basic definition of Petri nets—for instance, the coloured and higher level nets of Kurt Jensen arise through a simple modification of the sorts of the algebras underlying nets. Further, it provides a smooth formal relation with other models of concurrency such as Milner's calculus of communicating systems (CCS) and Hoare's communicating sequential processes (CSP), though this is only indicated in this paper.     

Goals,values, and reasoning

It is impossible to model human reasoning without taking into consideration the values and goals behind a decision. Although the problem of inference with values and goals has been discussed by a number of authors, many issues still stand in need of further development. The main purpose of this work is to discuss the issue of modeling of values and goals in reasoning and argumentation, hence the need for an analysis of existing definitions of values and goals, a discussion of relations between them, and the formulation of value- and goal-based mechanisms of reasoning.     

Motility,mixing, and multicellularity

A fundamental issue in evolutionary biology is the transition from unicellular to multicellular organisms, and the cellular differentiation that accompanies the increase in group size. Here we consider recent results on two types of “multicellular” systems, one produced by many unicellular organisms acting collectively, and another that is permanently multicellular. The former system is represented by groups of the bacterium Bacillus subtilis and the latter is represented by members of the colonial volvocalean green algae. In these flagellated organisms, the biology of chemotaxis, metabolism and cell–cell signaling is intimately connected to the physics of buoyancy, motility, diffusion, and mixing. Our results include the discovery in bacterial suspensions of intermittent episodes of disorder and collective coherence characterized by transient, recurring vortex streets and high-speed jets of cooperative swimming. These flow structures markedly enhance transport of passive tracers, and therefore likely have significant implications for intercellular communication. Experiments on the Volvocales reveal that the sterile flagellated somatic cells arrayed on the surface of Volvox colonies are not only important for allowing motion toward light (phototaxis), but also play a crucial role in driving fluid flows that transport dissolved molecular species. These flows, generated by the collective beating of flagella, confer a synergistic advantage with regard to transport of nutrients and chemical messengers. They allow these species to circumvent a nutrient acquisition bottleneck which would exist if transport were purely diffusive, and thereby evolve to larger multicellular individuals. In both cases, a higher level of organization, specialization and complexity counteract the higher costs inherent to larger groups.     

Budgets, Blood, and Turnips

Although the need for new systems (instead of constant maintenance of older systems) is often quite apparent to the MIS department, their advantages are not so readily realized by senior management -which sees only costs and risks instead of benefits. As a result, MIS managers must prove the costs and benefits of such projects. This column examines the difficulty of measuring the costs and benefits of four generations of systems -batch, online, DBMS based, and maintenance motivated - and explains why MIS managers should not only rewrite old systems but turn their attention toward the development of new and innovative systems.     

Similarity,topology, and uniformity

We generalize various notions of generalized metrics even further to one general concept comprising them all. For convenience, we turn around the ordering in the target domain of the generalized metrics so that we speak of similarity instead of distance. Starting from an extremely general situation without axioms, we examine which axioms or additional properties are needed to obtain useful results. For instance, we shall see that commutativity and associativity of the generalized version of addition occurring in the triangle inequality are not really needed, nor do we require a generalized version of subtraction.Each similarity space comes with its own domain of possible similarity values. Therefore, we consider non-expanding functions modulo some rescaling between different domains of similarity values. We show that non-expanding functions with locally varying rescaling functions correspond to topologically continuous functions, while non-expanding functions with a globally fixed rescaling generalize uniformly continuous functions.     

Work, Retirement, and Depression

This study investigates the relationship between depression and labor force participation by examining whether retirement induces depression or depression discourages labor force participation. The sample is drawn from newly available, nationally representative data of those 50–64 years old using the 2006 Korean Longitudinal Study of Aging. We model two possibly inter-related outcomes; depression and work. We first examine whether retirement influences depression, using the mandatory retirement provisions of the Korean labor force to identify a pathway to retirement that is not a consequence of depression. We then estimate the determinants of current work using instrumental variables for depression. We find that mandatory retirement is not associated with subsequent depression but find evidence that depression leads to reduced labor force participation, after using instrumental variables to predict the existence of depressive symptoms among respondents. We find strong evidence that depression leads to reduced labor force participation. Although retirees are often more depressed than workers, the causes that induce retirement, such as poor health, care-giving responsibilities, and inability to find a job, are also associated with depression.     

DRM, Complexity, and Correctness

Steve Bellovin looks at the complex code behind Microsoft Vista and its DRM mechanisms. Increased amounts of code add to insecurity, but the real danger with DRM is with increased interaction among different pieces of code. A lot of new mechanisms have been introduced; more seriously, a lot of new communications paths and dependencies have been introduced. Worst of all, these paths and mechanisms are solving a new problem, one with which the profession has very little experience. Did Microsoft get it right?     

Electronic Markets, Hierarchies, Hubs, and Intermediaries

The impact of information technologies on organizations is difficult to predict, although critical for developing comprehensive organizational strategies. Much of the difficulty is traceable to the treatment of all information technologies as a single factor, when in fact different technologies may have drastically different impacts on the organization. Specifically, the distinction between two general classes of technologies, communication and information processing technologies, is studied. An analytical model is developed to show that these two classes of technologies have exactly the opposite impacts on the organization. Moreover, the impact also depends on the organization, and its existing structure. Communication intensive and processing intensive organizational structures are distinguished and they are shown to be impacted differently by information technologies. An analytical framework is developed to show a continuum of organizational structures, depending on their relative communication and processing intensity, and the effect of various technologies is shown to be to move the organization along that continuum. Communication and information processing technologies are shown to move the organization in opposing directions. Finally, the analytical framework is shown to be robust and valid under a wide variety of conditions, covering most real life organizations.     

Quantifiers, Anaphora, and Intensionality

The relationship between Lexical-Functional Grammar (LFG) functional structures (f-structures) for sentences and their semanticinterpretations can be formalized in linear logic in a way thatcorrectly explains the observed interactions between quantifier scopeambiguity, bound anaphora and intensionality.Our linear-logic formalization of the compositional properties ofquantifying expressions in natural language obviates the need forspecial mechanisms, such as Cooper storage, in representing thescoping possibilities of quantifying expressions. Instead, thesemantic contribution of a quantifier is recorded as a linear-logicformula whose use in a proof will establish the scope of thequantifier. Different proofs can lead to different scopes. In eachcomplete proof, the properties of linear logic ensure thatquantifiers are properly scoped.The interactions between quantified NPs and intensional verbs such asseek are also accounted for in this deductive setting. A singlespecification in linear logic of the argument requirements ofintensional verbs is sufficient to derive the correct readingpredictions for intensional-verb clauses both with nonquantified andwith quantified direct objects. In particular, both de dictoand de re readings are derived for quantified objects. Theeffects of type-raising or quantifying-in rules in other frameworksjust follow here as linear-logic theorems.While our approach resembles current categorial approaches inimportant ways (Moortgat, 1988, 1992a; Carpenter, 1993; Morrill, 1994)it differs from them in allowing the greater compositional flexibility ofcategorial semantics (van Benthem, 1991)while maintaining a precise connection to syntax. As a result, we areable to provide derivations for certain readings of sentences withintensional verbs and complex direct objects whose derivation inpurely categorial accounts of the syntax-semantics interface appearsto require otherwise unnecessary semantic decompositions of lexicalentries.     

Logic,topology, and integration

The central notion presented is that of closeness of (or difference between) two theories. In the first part, we give intuitive arguments in favor of considering topologies on the set of theories, continuous logics, and the average difference between two logics (i.e., the integral of their difference). We argue for the importance of the difference between theories in a wide range of applications and problems. In the second part, we give some basic definitions and results for one such type of topology. In particular, separation properties and compactness are discussed and examples given. The techniques employed for constructing the topology are also used for defining a -algebra of measurable sets on the set of theories, leading to the usual definition of the Lebesgue integral and a precise definition of the average difference of two logics.     

Children, robotics, and education

Popular interest in robotics has increased astonishingly in the last few years. Robotics is seen by many as offering major new benefits in education at all levels. Before rushing to exploit this popularity, educators should ask serious questions about the universality and longevity of the robotics phenomenon. Is it a fashion? To be useful, the energy released by robotics must be sustained and universal, and the means of exploiting it must be systematic. Universities define their own robotics curriculum, but most schools lack both the resources and the freedom to do this, and must work with a national curriculum. If it can be shown that robotics has sustained potential in education, it seems inevitable that new ways need to be found to integrate it into the school curriculum.     

Recipes,Algorithms, and Programs

In the technical literature of computer science, the concept of an effective procedure is closely associated with the notion of an instruction that precisely specifies an action. Turing machine instructions are held up as providing paragons of instructions that "precisely describe" or "well define" the actions they prescribe. Numerical algorithms and computer programs are judged effective just insofar as they are thought to be translatable into Turing machine programs. Nontechnical procedures (e.g., recipes, methods) are summarily dismissed as ineffective on the grounds that their instructions lack the requisite precision. But despite the pivotal role played by the notion of a precisely specified instruction in classifying procedures as effective and ineffective, little attention has been paid to the manner in which instructions "precisely specify" the actions they prescribe. It is the purpose of this paper to remedy this defect. The results are startling. The reputed exemplary precision of Turing machine instructions turns out to be a myth. Indeed, the most precise specifications of action are provided not by the procedures of theoretical computer science and mathematics (algorithms) but rather by the nontechnical procedures of everyday life. I close with a discussion of some of the rumifications of these conclusions for understanding and designing concrete computers and their programming languages.     

Mandalas,screws, pears,and Klein bottles

The goal of this article is to present an informal introduction and tutorial on the production of aesthetically pleasing solid models. The article is intended for the nonmathematical reader interested in computer art. Simple generating formulas and recipes are included.     

Past, Present, and Future

Thomas L. Friedman. the World Is Flat: A Brief History of the Twenty-First Century. N ew York: Farrar, Straus and Giroux, 2005, 488 pp.

Nicholas G. Carr. Does IT Matter? Information Technology and the Corrosion of Competitive Advantage. Boston: Harvard Business School Press, 2004, 193 pp.

John Hagel III and John Seely Brown. the Only Sustainable Edge: Why Business Strategy Depends on Productive Friction and Dynamic Specialization. Boston: Harvard Business School Press, 2005, 218 pp.

John Markoff. What the Dormouse Said. New York: Viking, 2005, 301 pp.     

Rats, robots, and rescue

In early May, media inquiries started arriving at my office at the Center for Robot-Assisted Search and Rescue (www.crasar.org). Because I'm CRASAR's director, I thought the press was calling to follow up on the recent humanitarian award given to the center's founder, John Blitch, for successfully using small, backpackable robots at the World Trade Center disaster. Instead, I found they were asking me to comment on the "roborats" study in the 2 May 2002 Nature. In this study, rats with medial force brain implants underwent operant conditioning to force them into a form of guided behavior, one aspect of which was thought useful for search and rescue. The article's closing comment suggested that a guided rat could serve as both a mobile robot and a biological sensor. Although a roboticist by training, I'm committed to any technology that will help save lives while reducing the risk to rescuers. But rats?.     

Google, Profiling, and Privacy

Antitrust questions put a useful spotlight on the privacy issues of online profiling by those who sell advertising on the Web. These questions apply not just to Google but to any site that uses personal information and behavior data to develop and use individual users' profiles. But simply assuring advertisers a fair marketplace won't be sufficient to guarantee user privacy. We know that many users are willing to give up some privacy protection for short-term convenience, but we shouldn't conclude from these chokes that privacy means the sum total of whatever people end up choosing.