Ricardo M. Czekster

GTAexpress: A Software Package to Handle Kronecker Descriptors

This paper presents a software package, called GTAexpress, to handle structured continuous-time Markovian models expressed using Generalized Tensor Algebra, also known as, Kronecker descriptors. The proposed software package has the most advanced methods to provide stationary and transient solutions as well as some basic structural properties of models represented as a sum of generalized tensor products. Other software tools already provide some approaches based on tensor representation, like, PEPS and SMART. However, such tools are bounded to a specific modeling formalism. The basic idea of GTAexpress is to provide Kronecker descriptor-based solutions that can be easily used as a package in new tools or as a library in the existing high-level formalisms tools.

Analytical Modeling of Software Development Teams in Globally Distributed Projects

Global software engineering is an area of increasing research challenges, in which teams are dispersed in multiple sites collaborating across borders and time zones. In spite of its potential competitive advantages, globally distributed projects must deal with difficulties when distributing resources such as teams with cultural diversities, different skills and experience levels. Both industry and academia demonstrate a special interest in the modeling and prediction, mainly representing systems in order to extract interesting indices, for example, evaluating whether or not a project will succeed. This paper demonstrates the usefulness of analytical modeling techniques in order to predict the outcome of geographically-distributed projects. We focus our attention to the participants interaction and its interplay when it affects team productivity. The models are parametrized considering single-site and multi-site scenarios, varying resources availability, teams expertise and support levels. Performance indices from both scenarios are presented and conclusion indicates possible model extensions.

Efficient vector-descriptor product exploiting time-memory trade-offs

The description of large state spaces through stochastic structured modeling formalisms like stochastic Petri nets, stochastic automata networks and performance evaluation process algebra usually represent the infinitesimal generator of the underlying Markov chain as a Kronecker descriptor instead of a single large sparse matrix. The best known algorithms used to compute iterative solutions of such structured models are: the pure sparse solution approach, an algorithm that can be very time efficient, and almost always memory prohibitive; the Shuffle algorithm which performs the product of a descriptor by a probability vector with a very impressive memory efficiency; and a newer option that offers a trade-off between time and memory savings, the Split algorithm. This paper presents a comparison of these algorithms solving some examples of structured Kronecker represented models in order to numerically illustrate the gains achieved considering each models characteristics.

Stochastic Model for QoS Assessment in Multi-tier Web Services

Service Level Agreements (SLAs) are used to guarantee quality of service (QoS) between customers and service providers. In an SLA, parties establish a common set of rules and responsibilities. In this paper we propose a practical stochastic modeling of a multi-tier architecture considering SLAs for specific transactions. The model is parameterized with available performance testing data for a real web service, and with a testing environment having unpredictable and unknown external workloads of simultaneous execution. In addition, we present multiple scenarios of external applications impacting on the SLAs in our target architecture. Having a previous knowledge about the average time demanded by some external applications, our model results can provide evidences when the system under test will not respect the agreed-upon SLAs. Finally, we discuss possible model extensions towards further unknown workload characterizations and considerations about application execution profiling.

Kronecker descriptor partitioning for parallel algorithms

The key operation to obtain stationary and transient solutions of transition systems described by Kronecker structured formalisms is the Vector-Descriptor product. This operation is usually performed with shuffling operations and matrices aggregations to reduce the floating point multiplications inside iterative methods. Due to the flexibility of the Split method treating Kronecker product terms, it is a natural alternative to decompose descriptors within parallel environments. The main problem is to define the correct task size to assign to each node and also the shared memory size, since sending a small task per time can lead to a larger communication overhead. In this paper we are investigating data partitioning strategies for a parallel solution of transition systems obtained from Kronecker descriptors using the Split algorithm.

Follow-the-Sun Methodology in a Stochastic Modeling Perspective

Stochastic modeling of globally distributed projects has become a way to evaluate the performance of teams working in different time zones. The interest in extracting and analyzing quantitative data from geographically dispersed teams has grown throughout the years as major development companies were attracted by potential benefits. We direct our attention to Follow-The-Sun (FTS), a special case of globally distributed projects, where work is handed off every day from one development site to the next on a different time zone. The main benefit of FTS is to reduce project duration providing continuous software development. Our objective in this paper is to discuss a formal mapping of FTS characteristics to a stochastic model in order to predict performance indices of teams such as availability and risk assessment. The modeling effort aims to enhance understanding and feasibility evaluation for FTS projects.

Improving Productivity of Local Software Development Teams in a Global Software Development Environment

New guidelines and methods for teams and organizational structures are crucial to improve efficiency and scalability for globally distributed software development. Our work introduces a simplified process to be used by local teams working globally. The process is derived from the Agile Unified Process proposal and is highly centered in team motivation using game principles

Software Aging and Rejuvenation for Increased Resilience: Modeling, Analysis and Applications

Software aging and rejuvenation research has shown that the application of approaches for software aging modeling, monitoring, and rejuvenation has the potential to significantly increase software resilience. In this chapter, we present an overview of important analytical models and measurement approaches for software aging and rejuvenation. We start by describing the Markov based approaches and renewal process based approaches for software aging and rejuvenation modeling. In addition, we present measurement based approaches using both online and offline methods for software rejuvenation. We conclude by presenting a categorization of the approaches and by presenting a brief overview of applicability of each of the approaches presented in this chapter.

Performance Issues for Parallel Implementations of Bootstrap Simulation Algorithm

The solution of state-based stochastic models is usually a demanding application, then it is a natural subject to high performance techniques. We are particularly interested in the speedup of Bootstrap Simulation of structured Markovian models. This approach is a quite recent development in the performance evaluation area, and it brings a considerable improvement in the results accuracy, despite the intrinsic effect of randomness in simulation experiments. Unfortunately, Bootstrap Simulation has higher computational cost than other alternatives. We present experiments with different options to optimize the parallel solution of Bootstrap Simulation applied to three practical examples described in Stochastic Automata Networks (SAN) formalism. This paper contribution resides in the discussion of theoretical implementation issues, the obtained speedup and the actual processing and communication times for all experiments. Additionally, we also suggest future works to improve even more the proposed solution and we discuss some interesting insights for parallelization of similar applications.

SimVIZ : a desktop virtual environment for visualization and analysis of protein multiple simulation trajectories

In silico protein conformation simulation generates massive amounts of data which needs to be properly visualized and analyzed. We are applying Desktop Information-Rich Virtual Environments (Desktop IRVE’s) techniques and concepts to aid multiple trajectory simulation analysis, improving user experience and developing a problem-solving environment to help the decision making process. We will present SimVIZ, a tool which integrates visualization to simulation analysis, improving previous knowledge about trajectories. This environment shows informative panels, Contact Maps, RMSD charts, the Ramachandran Plot and a Parallel Coordinate multidimensional visualization of simulation output in a single rendering scene. SimVIZ also opens multiple trajectories along with user associated information concerning many aspects of the simulation. SimVIZ is an integrated problem solving environment of multiple trajectories of protein simulations, offering various kinds of analysis and visualization tools used by the community to validate protein structures or to gather a better understanding of the protein folding process.