Cristina Videira Lopes

A study on exception detection and handling using aspect-oriented programming

Aspect oriented programming (AOP) is intended to ease situations that involve many kinds of code tangling. The paper reports on a study to investigate AOPs ability to ease tangling related to exception detection and handling. We took an existing framework written in Java/sup TM/, the JWAM framework, and partially reengineered its exception detection and handling aspects using AspectJ/sup TM/, an aspect oriented programming extension to Java. We found that AspectJ supported implementations that drastically reduced the portion of the code related to exception detection and handling. In one scenario, we were able to reduce that code by a factor of 4. We also found that, with respect to the original implementation in plain Java, AspectJ provided better support for different configurations of exceptional behaviors, more tolerance for changes in the specifications of exceptional behaviors, better support for incremental development, better reuse, automatic enforcement of contracts in applications that use the framework, and cleaner program texts. We also found some weaknesses of AspectJ that should be addressed in the future.

A survey, classification and comparative analysis of medium access control protocols for ad hoc networks

Recent technological advances in wireless communications offer new opportunities and challenges for wireless ad hoc networking. In the absence of the fixed infrastructure that characterizes traditional wireless networks, control and management of wireless ad hoc networks must be distributed across the nodes, thus requiring carefully designed medium access control (MAC) layer protocols. In this article we survey, classify, and analyze 34 MAC layer protocols for wireless ad hoc networks, ranging from industry standards to research proposals. Through this analysis, six key features emerge: (1) channel separation and access; (2) topology; (3) power; (4) transmission initiation; (5) traffic load and scalability; and (6) range. These features allow us to characterize and classify the protocols, to analyze the tradeoffs produced by different design decisions, and to assess the suitability of various design combinations for ad hoc network applications. The classification and the tradeoff analysis yield design guidelines for future wireless ad hoc network MAC layer protocols.

Sourcerer: a search engine for open source code supporting structure-based search

We present Sourcerer, a search engine for open-source code. Sourcerer extracts fine-grained structural information from the code and stores it in a relational model. This information is used to implement a basic notion of CodeRank and to enable search forms that go beyond conventional keyword-based searches.

Adaptive Low Power Listening for Wireless Sensor Networks

Most sensor networks require application-specific network-wide performance guarantees, suggesting the need for global and flexible network optimization. The dynamic and nonuniform local states of individual nodes in sensor networks complicate global optimization. Here, we present a cross-layer framework for optimizing global power consumption and balancing the load in sensor networks through greedy local decisions. Our framework enables each node to use its local and neighborhood state information to adapt its routing and MAC layer behavior. The framework employs a flexible cost function at the routing layer and adaptive duty cycles at the MAC layer in order to adapt a nodes behavior to its local state. We identify three state aspects that impact energy consumption: 1) number of descendants in the routing tree, 2) radio duty cycle, and 3) role. We conduct experiments on a test-bed of 14 mica2 sensor nodes to compare the state representations and to evaluate the frameworks energy benefits. The experiments show that the degree of load balancing increases for expanded state representations. The experiments also reveal that all state representations in our framework reduce global power consumption in the range of one-third for a time-driven monitoring network and in the range of one-fifth for an event-driven target tracking network.

Open implementation design guidelines

Designing reusable software modules can be extremely difficult. The design must be balanced between being general enough to address the needs of a wide range of clients and being focused enough to truly satisfy the requirements of each specific client. One area where it can be particularly difficult to strike this balance is in the implementation strategy of the module. The problem is that general-purpose implementation strategies, tuned for a wide range of clients, aren’t necessarily optimal for each specific client— this is especially an issue for modules that are intended to be reusable and yet provide highperformance. An examination of existing software systems shows that an increasingly important technique for handling this problem is to design the module’s interface in such a way that the client can assist or participate in the selection of the module’s implementation strategy. We call this approach open implementation. When designing the interface to a module that allows its clients some control over its implementation strategy, it is important to retain, as much as possible, the advantages of traditional closed implementation modules. This paper explores issues in the design of interfaces to open implementation modules. We identify key design choices, and present guidelines for deciding which choices are likely to work best in particular situations.

A theory of aspects as latent topics

After more than 10 years, Aspect-Oriented Programming (AOP) is still a controversial idea. While the concept of aspects appeals to everyones intuitions, concrete AOP solutions often fail to convince researchers and practitioners alike. This discrepancy results in part from a lack of an adequate theory of aspects, which in turn leads to the development of AOP solutions that are useful in limited situations. We propose a new theory of aspects that can be summarized as follows: concerns are latent topics that can be automatically extracted using statistical topic modeling techniques adapted to software. Software scattering and tangling can be measured precisely by the entropies of the underlying topic-over-files and files-over-topics distributions. Aspects are latent topics with high scattering entropy. The theory is validated empirically on both the large scale, with a study of 4,632 Java projects, and the small scale, with a study of 5 individual projects. From these analyses, we identify two dozen topics that emerge as general-purpose aspects across multiple projects, as well as project-specific topics/concerns. The approach is also shown to produce results that are compatible with previous methods for identifying aspects, and also extends them. Our work provides not only a concrete approach for identifying aspects at several scales in an unsupervised manner but, more importantly, a formulation of AOP grounded in information theory. The understanding of aspects under this new perspective makes additional progress toward the design of models and tools that facilitate software development.

Beep: 3D indoor positioning using audible sound

Rapid growth in the number of wireless enabled devices has led to an increased interest in location-aware applications. The backbone of such applications is provided by a location system. In this paper we present Beep, an indoor location system that senses audible sound. The use of audible sound makes our system cheap and easily deplorable to most existing roaming devices. Unlike positioning systems using ultrasound and infrared signals, Beep does not require the user to carry any kind of specialized hardware. Our system is based on standard 3D multilateration algorithms. However, the requirement of being able to locate existing devices, whose sound cards were not designed for high-precision signaling, introduces additional challenges to the location problem. This paper describes how those problems were solved and presents experimental results. Beep works with an accuracy of about 2 feet in more than 97% cases. The paper also describes a sensor deployment strategy that requires low sensor density and consequently low installation costs.

Recent Developments in AspectJ

This paper summarizes the latest developments in AspectJ, a general-purpose aspect-oriented programming (AOP) extension to Java. Some examples of aspects are shown. Based on our experience in designing language extensions for AOP, we also present a design space for AOP languages that may be of interest to the AOP community.

Bagging gradient-boosted trees for high precision, low variance ranking models

Recent studies have shown that boosting provides excellent predictive performance across a wide variety of tasks. In Learning-to-rank, boosted models such as RankBoost and LambdaMART have been shown to be among the best performing learning methods based on evaluations on public data sets. In this paper, we show how the combination of bagging as a variance reduction technique and boosting as a bias reduction technique can result in very high precision and low variance ranking models. We perform thousands of parameter tuning experiments for LambdaMART to achieve a high precision boosting model. Then we show that a bagged ensemble of such LambdaMART boosted models results in higher accuracy ranking models while also reducing variance as much as 50%. We report our results on three public learning-to-rank data sets using four metrics. Bagged LamdbaMART outperforms all previously reported results on ten of the twelve comparisons, and bagged LambdaMART outperforms non-bagged LambdaMART on all twelve comparisons. For example, wrapping bagging around LambdaMART increases NDCG@1 from 0.4137 to 0.4200 on the MQ2007 data set; the best prior results in the literature for this data set is 0.4134 by RankBoost.

An analysis of modularity in aspect oriented design

We present an analysis of modularity in aspect oriented design using the theory of modular design developed by Baldwin and Clark [10]. We use the three major elements of that theory, namely: i) Design Structure Matrix (DSM), an analysis and modeling tool; ii) Modular Operators, units of variations for design evolution; and iii) Net Options Value (NOV), a quantitative approach to evaluate design. We study the design evolution of a Web Services application where we observe the effects of applying aspect oriented modularization.Based on our analysis we get to the following three main conclusions. First, on the structural part, it is possible to apply the DSM to aspect oriented modularizations in a straightforward manner, i.e. without modifications to DSMs basic model. This shows that aspects can, in fact, be treated as modules of design. Second, the evolution of a design into including aspect modules uses the modular operators proposed by Baldwin and Clark, with a variant of the Inversion operator. This variant captures taking redundant, scattered information hidden in modules and moving it down or keeping it at the same level in the design hierarchy. Third, when calculating and comparing NOVs of the different designs of our application, we obtained higher NOV for the design with aspects than for the design without aspects. This shows that, under this theory of modularity, certain aspect oriented modularizations can add value to the design.