Hassan Charaf

A Systematic Approach to Metamodeling Environments and Model Transformation Systems in VMTS

Highly configurable metamodeling environments and graph transformation techniques have been applied successfully in software system modeling and other areas. In this paper a uniform treatment of these two methods is illustrated by a tool called Visual Modeling and Transformation System. The concepts of an n-layer metamodeling environment is outlined with the related topological and attribute issues. Built on metamodeling techniques two alternatives for model transformation are elaborated, namely, the traversal and the graph-rewriting approaches. In our implementation all of the aforementioned mechanisms use metamodel as a common formalism, which can be considered as a uniform basis for storing, creating and transforming visual languages. The feasibility of the approach is illustrated by a transformation which generates C/C++ code from UML statecharts.

Model Reuse with Metamodel-Based Transformations

Metamodel-based transformations permit descriptions of mappings between models created using different concepts from possibly overlapping domains. This paper describes the basic algorithms used in matching metamodel constructs, and how this match is to be applied. The transformation process facilitates the reuse of models specified in one domain-specific modeling language in another context: another domain-specific modeling language. UML class diagrams are used as the language of the metamodels. The focus of the paper is on the matching and firing of transformation rules, and on finding efficient and generic algorithms. An illustrative case study is provided.

Novel concepts for device-to-device communication using network coding

Device-to-device communication is currently a hot research topic within 3GPP. Even though D2D communication has been part of previous ad hoc, meshed and sensor networks proposals, the main contribution by 3GPP is that the direct communication among two devices is carried out over a dynamically assigned, licensed spectrum; thus, it is under full control of the cellular network. D2D communication creates a market potential for new services, new approaches to efficient spectrum use, and security concepts. This is especially true if D2D communication is extended to larger communication groups organized in meshed clusters. In this article, we discuss the potential and shortcomings of D2D communication as proposed today, advocating for the use of network coding as an enabling technology for enhanced security and communication efficiency using the PlayNCool and CORE protocols as key examples to deliver smarter D2D systems.

Synchronized multimedia streaming on the iPhone platform with network coding

This paper presents the implementation of synchronized multimedia streaming for the Apple iPhone platform. The idea is to stream multimedia content from a single source to multiple receivers with direct or multi-hop connections to the source. First we look into existing solutions for video streaming on the iPhone for point-to-point architectures. After acknowledging their limitations, we propose a solution based on network coding to efficiently and reliably deliver the multimedia content to many devices in a synchronized manner. Then we introduce an application that implements this technique on the iPhone. We also present our testbed which consists of 16 iPod Touch devices to showcase the capabilities of our application.

Implementation of random linear network coding on OpenGL-enabled graphics cards

This paper describes the implementation of network coding on OpenGL-enabled graphics cards. Network coding is an interesting approach to increase the capacity and robustness in multi-hop networks. The current problem is to implement random linear network coding on mobile devices which are limited in computational power, energy, and memory. Some mobile devices are equipped with a 3D graphics accelerator, which could be used to do most of the RLNC related calculations. Such a cross-over have already been used in computationally demanding research tasks as in physics or medicine. As a first step the paper focuses on the implementation of RLNC using the OpenGL library and NVidias Cg toolkit on desktop PCs and laptops. Several measurement results show that the implementation on the graphics accelerator is outperforming the CPU by a significant margin. The OpenGL implementation performs relatively better with larger generation sizes due to the parallel nature of GPUs. Therefore the paper shows an appealing solution for the future to perform network coding on mobile devices.

Investigating factors influencing the response time in ASP.NET web applications

Distributed systems and network applications play an important role in computer science nowadays. The most common consideration is performance, because these systems have to provide cost-effective and high availability services in the long term, thus they have to be scaled to meet the expected load. The performance of a web application is affected by several factors. The goal of our work is to analyze how some of them affect the response time. The paper presents the result of performance measurements of an ASP.NET web application. We measured the average response time of a test web application while changing the parameters of the application server. The results are analyzed using statistical methods: (i) independence tests to investigate which factors influence principally the performance, (ii) in addition certain plots and hypothesis tests to determine the distribution of the response time.

Metamodel-Based Model Transformation with Aspect-Oriented Constraints

Model transformation means converting an input model available at the beginning of the transformation process to an output model. A widely used approach to model transformation uses graph rewriting as the underlying transformation technique. In case of diagrammatic languages, such as the Unified Modeling Language (UML), the exclusive topological matching is found to be not enough. To define precisely the transformation steps beyond the topology of the visual models, additional constraints must be specified which ensures the correctness of the attributes, or other properties to be enforced. Dealing with OCL constraints provides a solution for these unsolved issues, because topological and attribute transformation methods cannot perform and express the problems which can be addressed by constraint validation. The use of OCL as a constraint and query language in modeling is essential. We have shown that it can be applied to model transformations as well. Often, the same constraint is repetitiously applied in many different places in a transformation. It would be beneficial to describe a common constraint in a modular manner, and to designate the places where it is to be applied. This paper presents the problem of crosscutting constraints in transformation rules, and provides an aspect-oriented solution for it. Our approach makes it possible to define constraints separately from the transformation steps, and facilitates specifying their propagation assignment to graph transformation rules. To illustrate the conceptual results, a case study is also provided, which introduces (i) how our approach generates user interface handler source code for mobile platform from a resource model and a statechart diagram, and (ii) how it validates specific properties during the transformation steps using aspect-oriented constraints.

A Synchronizing Technique for Syntactic Model-Code Round-Trip Engineering

The introduction of UML class diagrams has not raised the abstraction level of development to the extent that was intended: class diagrams are only the visual representations of source class skeletons implemented in a programming language. To improve the productivity, domain-specific languages are applied, which cover a narrow domain, and their high abstraction makes use of the domain experts easier. The simultaneous evolution of the source code and the software models causes the loss of synchronization. Round-tripping the domain-specific models is not supported by model-driven development tools, because the abstraction gap between the models and the generated code prevents the use of general approaches. However, developers should have the opportunity of choosing between the artifacts that are more efficient for applying the modifications. This paper introduces how different tools achieve the preservation of manually written code while the model is evolving. In contrast, we present our approach that allows the customization of the generated code. The abstraction gap is closed by performing model transformations and an incremental merge.

Retrieving frequent walks from tracking data in RFID-equipped warehouses

The utilization of RFID-related (radio-frequency identification) technologies became very common in the last few years. The effected main areas are highway surveillance systems, access cards, transport payments, RFID passports and product tracking systems. Tagged products can be tracked in an appropriately equipped warehouse with the help of the installed RFID readers. The movement of the customers can be followed because of a tag attached to the shopping cart or the products stored in it. In this paper, assuming such an environment, it has been examined how relevant information can be retrieved with the help of data mining methods from the collected, RFID-related data. The frequent sequences have been extracted, revealing the most visited spots and walks across the warehouse and the typical products selected along the way.

Performance Factors in ASP.NET Web Applications with Limited Queue Models

Distributed systems and Web applications play an important role in computer science nowadays. The most common consideration is performance, because these systems must provide services with low response time, high availability, and certain throughput level. The performance of a Web application is affected by several factors. The goal of our work is to analyze how some of them affect the response time. In this paper, the effects of two configurable settings of the ASP.NET application server are discussed: the limit of the global queue and the limit of the application queue. The response time of a test Web application are measured, while changing these settings. The results are analyzed in a qualitative manner which is followed by using statistical methods: independence tests to investigate which factors influence principally the performance. Our experiments have shown that the global queue limit and the application queue limit are performance factors. Finally, optimal settings according to the performance-related requirements are determined as a function of client workload and the settings of the thread pool attributes