Pinocchio: Bringing Reflection to Life with First-Class Interpreters

To support development tools like debuggers, runtime systems need to provide a meta-programming interface to alter their semantics and access internal data. Reflective capabilities are typically fixed by the Virtual Machine (VM). Unanticipated reflective features must either be simulated by complex program transformations, or they require the development of a specially tailored VM. We propose a novel approach to behavioral reflection that eliminates the barrier between applications and the VM by manipulating an explicit tower of first-class interpreters. Pinocchio is a proof-of-concept implementation of our approach which enables radical changes to the interpretation of programs by explicitly instantiating subclasses of the base interpreter. We illustrate the design of Pinocchio through non-trivial examples that extend runtime semantics to support debugging, parallel debugging, and back-in-time object-flow debugging. Although performance is not yet addressed, we also discuss numerous opportunities for optimization, which we believe will lead to a practical approach to behavioral reflection.

Embedding Languages Without Breaking Tools

Domain-specific languages (DSLs) are increasingly used as embedded languages within general-purpose host languages. DSLs provide a compact, dedicated syntax for specifying parts of an application related to specialized domains. Unfortunately, such language extensions typically do not integrate well with the development tools of the host language. Editors, compilers and debuggers are either unaware of the extensions, or must be adapted at a non-trivial cost. We present a novel approach to embed DSLs into an existing host language by leveraging the underlying representation of the host language used by these tools. Helvetia is an extensible system that intercepts the compilation pipeline of the Smalltalk host language to seamlessly integrate language extensions. We validate our approach by case studies that demonstrate three fundamentally different ways to extend or adapt the host language syntax and semantics.

Run-Time Evolution through Explicit Meta-Objects

Software must be constantly adapted due to evolving domain knowledge and unanticipated requirements changes. To adapt a system at run-time we need to reflect on its structure and its behavior. Object-oriented languages introduced reflection to deal with this issue, however, no reflective approach up to now has tried to provide a unified solution to both structural and behavioral reflection. This paper describes Albedo, a unified approach to structural and behavioral reflection. Albedo is a model of fined-grained unanticipated dynamic structural and behavioral adaptation. Instead of providing reflective capabilities as an external mechanism we integrate them deeply in the environment. We show how explicit meta-objects allow us to provide a range of reflective features and thereby evolve both application models and environments at run-time.

Service-Centric Networking

Content-centric networking is a novel paradigm for the Future Internet that treats content as a first class citizen. This paper argues that content-centric networking should be generalized towards a service-centric networking scheme. We propose a service-centric networking design based on an object-oriented approach, in which content and services are considered objects. We show implementation architectures for example services and how these can benefit from service-oriented networking.

The Influence of the Social and Cultural Environment on a Child's Playing in the First Three Years of Life

The research focused on children's behaviour in playing with objects both independently and in interaction with adults. It was based on studies of 40 Slovene children in 4 age groups (6,12,18 and 24 months) and of 23 Croatian children in 2 age groups (18 and 24 months). All the children were sampled proportionally by their gender and the educational level of their parents (middle and higher). Several coding check lists with satisfactory internal consistency were constructed during the study and used to analyse the video-recorded playing sessions with each child. The basic conclusion reached was that even in early childhood playing behaviour differs significantly between the infants from the two Central European countries. The difference lies not so much in the structure or the content of the playing actions, but in the way in which the infants deal playfully with the objects. This difference appears regardless of the type of object the infants are playing with and even regardless of the playing condition. It can best be described as the difference between the first significant discriminant function activity versus passivity. The Slovene infants were found to be on the active pole and the Croatians on the passive one. Social and gender differences were much less significant than cultural ones in determining the structure, the content and the way of playing. Significant age differences appeared in all three aspects, which was consistent with general trends in infants' psychological development. The group define the Slovene interactive playing style as object oriented, while the Croatian one was largely communicated oriented. Within the experimenter-infant dyads, children of both cultures played at a developmentally more advanced level than they did with their mothers, showing that the mothers were not as successful at reaching the ZPD as were the trained experimenters. In addition, the children of mothers who attributed more cognitive benefit to play played on a more advanced level than those whose mothers attributed more emotional benefit to play. The quality of the object the children were playing with was also significantly related to the structure, content and partly the way of dealing with the objects. Highly-structured objects stimulated complex play and low-structured ones stimulated simple play, regardless of playing conditions. The group concluded that both culture and the quality of the available object have an important impact on young children's play. Through the playing interaction, the infants internalise culturally specific patterns of behaviour and culturally specific meanings. These internalisations become apparent very early in their lives, even in non-social situations. On the other hand, the objects themselves have an impact on the level of infants' play. When they do not provide sufficient perceptive and functional support for a representational action, the infants' play will lag behind their actual developmental capacities.

Using Smalltalk as a Reflective Executable Meta-Language

Object-oriented meta-languages such as MOF or EMOF are often used to specify domain specific languages. However, these meta-languages lack the ability to describe behavior or operational semantics. Several approaches used a subset of Java mixed with OCL as executable meta-languages. In this paper, we report our experience of using Smalltalk as an executable and integrated meta-language. We validated this approach in incrementally building over the last decade, Moose, a meta-described reengineering environment. The reflective capabilities of Smalltalk support a uniform way of letting the base developer focus on his tasks while at the same time allowing him to meta-describe his domain model. The advantage of our this approach is that the developer uses the same tools and environment

Capturing How Objects Flow At Runtime

Most of today's dynamic analysis approaches are based on method traces. However, in the case of object-orientation understanding program execution by analyzing method traces is complicated because the behavior of a program depends on the sharing and the transfer of object references (aliasing). We argue that trace-based dynamic analysis is at a too low level of abstraction for object-oriented systems. We propose a new approach that captures the life cycle of objects by explicitly taking into account object aliasing and how aliases propagate during the execution of the program. In this paper, we present in detail our new meta-model and discuss future tracks opened by it.

Bioconductor: Open software development for computational biology and bioinformatics

The Bioconductor project is an initiative for the collaborative creation of extensible software for computational biology and bioinformatics. We detail some of the design decisions, software paradigms and operational strategies that have allowed a small number of researchers to provide a wide variety of innovative, extensible, software solutions in a relatively short time. The use of an object oriented programming paradigm, the adoption and development of a software package system, designing by contract, distributed development and collaboration with other projects are elements of this project's success. Individually, each of these concepts are useful and important but when combined they have provided a strong basis for rapid development and deployment of innovative and flexible research software for scientific computation. A primary objective of this initiative is achievement of total remote reproducibility of novel algorithmic research results.

Dynamic Languages and Applications. Report on the Workshop Dyla 07 at ECOOP 2007

Following last two years’ workshop on dynamic languages at the ECOOP conference, the Dyla 2007 workshop was a successful and popular event. As its name implies, the workshop’s focus was on dynamic languages and their applications. Topics and discussions at the workshop included macro expansion mechanisms, extension of the method lookup algorithm, language interpretation, reflexivity and languages for mobile ad hoc networks. The main goal of this workshop was to bring together different dynamic language communities and favouring cross communities interaction. Dyla 2007 was organised as a full day meeting, partly devoted to presentation of submitted position papers and partly devoted to tool demonstration. All accepted papers can be downloaded from the workshop’s web site. In this report, we provide an overview of the presentations and a summary of discussions.

Risk analysis of light-frame wood construction due to multiple hazards

Light-frame wood buildings are widely built in the United States (U.S.). Natural hazards cause huge losses to light-frame wood construction. This study proposes methodologies and a framework to evaluate the performance and risk of light-frame wood construction. Performance-based engineering (PBE) aims to ensure that a building achieves the desired performance objectives when subjected to hazard loads. In this study, the collapse risk of a typical one-story light-frame wood building is determined using the Incremental Dynamic Analysis method. The collapse risks of buildings at four sites in the Eastern, Western, and Central regions of U.S. are evaluated. Various sources of uncertainties are considered in the collapse risk assessment so that the influence of uncertainties on the collapse risk of lightframe wood construction is evaluated. The collapse risks of the same building subjected to maximum considered earthquakes at different seismic zones are found to be non-uniform. In certain areas in the U.S., the snow accumulation is significant and causes huge economic losses and threatens life safety. Limited study has been performed to investigate the snow hazard when combined with a seismic hazard. A Filtered Poisson Process (FPP) model is developed in this study, overcoming the shortcomings of the typically used Bernoulli model. The FPP model is validated by comparing the simulation results to weather records obtained from the National Climatic Data Center. The FPP model is applied in the proposed framework to assess the risk of a light-frame wood building subjected to combined snow and earthquake loads. The snow accumulation has a significant influence on the seismic losses of the building. The Bernoulli snow model underestimates the seismic loss of buildings in areas with snow accumulation. An object-oriented framework is proposed in this study to performrisk assessment for lightframe wood construction. For home owners and stake holders, risks in terms of economic losses is much easier to understand than engineering parameters (e.g., inter story drift). The proposed framework is used in two applications. One is to assess the loss of the building subjected to mainshock-aftershock sequences. Aftershock and downtime costs are found to be important factors in the assessment of seismic losses. The framework is also applied to a wood building in the state of Washington to assess the loss of the building subjected to combined earthquake and snow loads. The proposed framework is proven to be an appropriate tool for risk assessment of buildings subjected to multiple hazards. Limitations and future works are also identified.

Test Blueprints - Exposing Side Effects in Execution Traces to Support Writing Unit Tests

Writing unit tests for legacy systems is a key maintenance task. When writing tests for object-oriented programs, objects need to be set up and the expected effects of executing the unit under test need to be verified. If developers lack internal knowledge of a system, the task of writing tests is non-trivial. To address this problem, we propose an approach that exposes side effects detected in example runs of the system and uses these side effects to guide the developer when writing tests. We introduce a visualization called Test Blueprint, through which we identify what the required fixture is and what assertions are needed to verify the correct behavior of a unit under test. The dynamic analysis technique that underlies our approach is based on both tracing method executions and on tracking the flow of objects at runtime. To demonstrate the usefulness of our approach we present results from two case studies.

Meta-Environment and Executable Meta-Language using Smalltalk: an Experience Report

Object-oriented modelling languages such as EMOF are often used to specify domain specific meta-models. However, these modelling languages lack the ability to describe behavior or operational semantics. Several approaches have used a subset of Java mixed with OCL as executable meta-languages. In this experience report we show how we use Smalltalk as an executable meta-language in the context of the Moose reengineering environment. We present how we implemented EMOF and its behavioral aspects. Over the last decade we validated this approach through incrementally building a meta-described reengineering environment. Such an approach bridges the gap between a code-oriented view and a meta-model driven one. It avoids the creation of yet another language and reuses the infrastructure and run-time of the underlying implementation language. It offers an uniform way of letting developers focus on their tasks while at the same time allowing them to meta-describe their domain model. The advantage of our approach is that developers use the same tools and environment they use for their regular tasks. Still the approach is not Smalltalk specific but can be applied to language offering an introspective API such as Ruby, Python, CLOS, Java and C#.

Exploiting Runtime Information in the IDE

Developers rely on the mechanisms provided by their IDE to browse and navigate a large software system. These mechanisms are usually based purely on a system's static source code. The static perspective, however, is not enough to understand an object-oriented program's behavior, in particular if implemented in a dynamic language. We propose to enhance IDEs with a program's runtime information (eg. message sends and type information) to support program comprehension through precise navigation and informative browsing. To precisely specify the type and amount of runtime data to gather about a system under development, dynamically and on demand, we adopt a technique known as partial behavioral reflection. We implemented navigation and browsing enhancements to an IDE that exploit this runtime information in a prototype called Hermion. We present preliminary validation of our experimental enhanced IDE by asking developers to assess its usefulness to understand an unfamiliar software system.