Nuno Carvalho

Scalable QoS-Based Event Routing in Publish-Subscribe Systems

This paper proposes a distributed and scalable publish-subscribe broker with support for QoS. The broker, called IndiQoS, leverages on existing mechanisms to reserve resources in the underlying network and on an overlay network of peer-to-peer rendezvous nodes, to automatically select QoS-capable paths. By avoiding flooding of either QoS reservations or link-state information, IndiQoS is able to scale with respect to network size and number of reservations. Experimental results show the validity of our approach

Emergent Structure in Unstructured Epidemic Multicast

In epidemic or gossip-based multicast protocols, each node simply relays each message to some random neighbors, such that all destinations receive it at least once with high probability. In sharp contrast, structured multicast protocols explicitly build and use a spanning tree to take advantage of efficient paths, and aim at having each message received exactly once. Unfortunately, when failures occur, the tree must be rebuilt. Gossiping thus provides simplicity and resilience at the expense of performance and resource efficiency. In this paper we propose a novel technique that exploits knowledge about the environment to schedule payload transmission when gossiping. The resulting protocol retains the desirable qualities of gossip, but approximates the performance of structured multicast. In some sense, instead of imposing structure by construction, we let it emerge from the operation of the gossip protocol. Experimental evaluation shows that this approach is effective even when knowledge about the environment is only approximate.

GORDA: An Open Architecture for Database Replication

Database replication has been a common feature in database management systems (DBMSs) for a long time. In particular, asynchronous or lazy propagation of updates provides a simple yet efficient way of increasing performance and data availability and is widely available across the DBMS product spectrum. High end systems additionally offer sophisticated conflict resolution and data propagation options as well as, synchronous replication based on distributed locking and two-phase commit protocols. This paper presents GORDA architecture and programming interface (GAPI), that enables different replication strategies to be implemented once and deployed in multiple DBMSs. This is achieved by proposing a reflective interface to transaction processing instead of relying on-client interfaces or ad-hoc server extensions. The proposed approach is thus cost-effective, in enabling reuse of replication protocols or components in multiple DBMSs, as well as potentially efficient, as it allows close coupling with DBMS internals.

On the use of a reflective architecture to augment Database Management Systems

The Database Management System (DBMS) used to be a commodity soft- ware component, with well known standard interfaces and semantics. However, the performance and reliability expectations being placed on DBMSs have increased the demand for a variety add-ons, that augment the functionality of the database in a wide range of deployment scenarios, offering support for features such as clustering, replica- tion, and self-management, among others. A well known software engineering approach to systems with such requirements is reflection. Unfortunately, standard reflective in- terfaces in DBMSs are very limited. Some of these limitations may be circumvented by implementing reflective features as a wrapper to the DBMS server. Unfortunately, these solutions comes at the expense of a large development effort and significant per- formance penalty. In this paper we propose a general purpose DBMS reflection architecture and interface, that supports multiple extensions while, at the same time, admitting efficient imple- mentations. We illustrate the usefulness of our proposal with concrete examples, and evaluate its cost and performance under different implementation strategies.

Ureteroscopy-assisted Percutaneous Kidney Access Made Easy: First Clinical Experience with a Novel Navigation System Using Electromagnetic Guidance (IDEAL Stage 1)

BACKGROUND Puncture of the renal collecting system represents a challenging step in percutaneous nephrolithotomy (PCNL). Limitations related to the use of standard fluoroscopic-based and ultrasound-based maneuvers have been recognized. OBJECTIVES To describe the technique and early clinical outcomes of a novel navigation system for percutaneous kidney access. DESIGN, SETTING, AND PARTICIPANTS This was a proof-of-concept study (IDEAL phase 1) conducted at a single academic center. Ten PCNL procedures were performed for patients with kidney stones. SURGICAL PROCEDURE Flexible ureterorenoscopy was performed to determine the optimal renal calyx for access. An electromagnetic sensor was inserted through the working channel. Then the selected calyx was punctured with a needle with a sensor on the tip guided by real-time three-dimensional images observed on the monitor. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS The primary endpoints were the accuracy and clinical applicability of the system in clinical use. Secondary endpoints were the time to successful puncture, the number of attempts for successful puncture, and complications. RESULTS AND LIMITATIONS Ten patients were enrolled in the study. The median age was 47.1 yr (30-63), median body mass index was 22.85kg/m2 (19-28.3), and median stone size was 2.13cm (1.5-2.5cm). All stones were in the renal pelvis. The Guys stone score was 1 in nine cases and 2 in one case. All 10 punctures of the collecting system were successfully completed at the first attempt without X-ray exposure. The median time to successful puncture starting from insertion of the needle was 20 s (range 15-35). No complications occurred. CONCLUSIONS We describe the first clinical application of a novel navigation system using real-time electromagnetic sensors for percutaneous kidney access. This new technology overcomes the intrinsic limitations of traditional methods of kidney access, allowing safe, precise, fast, and effective puncture of the renal collecting system. PATIENT SUMMARY We describe a new technology allowing safe and easy puncture of the kidney without radiation exposure. This could significantly facilitate one of the most challenging steps in percutaneous removal of kidney stones.

Experimental evaluation of distributed middleware with a virtualized Java environment

The correctness and performance of large scale service oriented systems depend on distributed middleware components performing various communication and coordination functions. It is, however, very difficult to experimentally assess such middleware components, as interesting behavior often arises exclusively in large scale settings, but such deployments are costly and time consuming. We address this challenge with Minha, a system that virtualizes multiple JVM instances within a single JVM while simulating key environment components, thus reproducing the concurrency, distribution, and performance characteristics of the actual system. The usefulness of Minha is demonstrated by applying it to the WS4D Java stack, a popular implementation of the Devices Profile for Web Services (DPWS) specification.

Conclave: Ontology-Driven Measurement of Semantic Relatedness between Source Code Elements and Problem Domain Concepts

Software maintainers are often challenged with source code changes to improve software systems, or eliminate defects, in unfamiliar programs. To undertake these tasks a sufficient understanding of the system (or at least a small part of it) is required. One of the most time consuming tasks of this process is locating which parts of the code are responsible for some key functionality or feature. Feature (or concept) location techniques address this problem. This paper introduces Conclave, an environment for software analysis, and in particular the Conclave-Mapper tool that provides a feature location facility. This tool explores natural language terms used in programs (e.g. function and variable names), and using textual analysis and a collection of Natural Language Processing techniques, computes synonymous sets of terms. These sets are used to score relatedness between program elements, and search queries or problem domain concepts, producing sorted ranks of program elements that address the search criteria, or concepts. An empirical study is also discussed to evaluate the underlying feature location technique.

An ontology toolkit for problem domain concept location in program comprehension

Programmers are able to understand source code because they are able to relate program elements (e.g. modules, objects, or functions), with the real world concepts these elements are addressing. The main goal of this work is to enhance current program comprehension by systematically creating bidirectional mappings between domain concepts and source code. To achieve this, semantic bridges are required between natural language terms used in the problem domain and program elements written using formal programming languages. These bridges are created by an inference engine over a multi-ontology environment, including an ontological representation of the program, the problem domain, and the real world effects program execution produces. These ontologies are populated with data collected from both domains, and enriched using available Natural Language Processing and Information Retrieval techniques.

From source code identifiers to natural language terms

Program comprehension techniques often explore program identifiers, to infer knowledge about programs. The relevance of source code identifiers as one relevant source of information about programs is already established in the literature, as well as their direct impact on future comprehension tasks.Most programming languages enforce some constrains on identifiers strings (e.g., white spaces or commas are not allowed). Also, programmers often use word combinations and abbreviations, to devise strings that represent single, or multiple, domain concepts in order to increase programming linguistic efficiency (convey more semantics writing less). These strings do not always use explicit marks to distinguish the terms used (e.g., CamelCase or underscores), so techniques often referred as hard splitting are not enough.This paper introduces Lingua::IdSplitter a dictionary based algorithm for splitting and expanding strings that compose multi-term identifiers. It explores the use of general programming and abbreviations dictionaries, but also a custom dictionary automatically generated from software natural language content, prone to include application domain terms and specific abbreviations. This approach was applied to two software packages, written in C, achieving a f-measure of around 90% for correctly splitting and expanding identifiers. A comparison with current state-of-the-art approaches is also presented.

Formal Verification of kLIBC with the WP Frama-C Plug-in

This paper presents our results in the formal verification of kLIBC, a minimalistic C library, using the Frama-C/WP tool. We report how we were able to completely verify a significant number of functions from string.h > and stdio.h >. We discuss difficulties encountered and describe in detail a problem in the implementation of common string.h > functions, for which we suggest alternative implementations. Our work shows that it is presently already viable to verify low-level C code, with heavy usage of pointers. Although the properties proved tend to be shallower as the code becomes of a lower-level nature, it is our view that this is an important direction towards real-world software verification, which cannot be attained by focusing on deep properties of cleaner code, written specifically to be verified.