In context of pervasive environment, the availability and reliability of Web services cannot be always guaranteed due to the dynamic and uncertain nature of these environments. Therefore, ensuring reliable and flexible service composition is one of the most difficult tasks. To overcome this problem, we propose an Event-B driven approach to easily design reliable and flexible Services compositions. We introduce a new paradigm, called dynamic transactional pattern. This new paradigm is a convergence concept of dynamic workflow patterns and advanced transactional model. It combines dynamic Control-Flow flexibility and transactional processing reliability. A composite Service is defined as a set of dynamic transactional patterns instances properly connected together. We show how the transactional behavior of a composite Service is automatically defined in an efficient way. In this work, we combine the modeling and verification activities related to formal development process supported by Event-B. The verification activity is based on theorems proving and model-checker. Afterwards, the model is validated using ProB animator in order to ensure that it behaves as expected.

International audienceThis paper proposes an algorithm for the robust reception of compressed HTML files transmitted over a noisy mobile radio channel. Both source encoders and transmission systems are assumed to be standard compliant. The source encoder follows the HTTP1.1 protocol specifications, i.e. the HTML files are encoded by the deflate algorithm, a combination of Lempel-Ziv and Huffman algorithms. The transmission scheme follows IEEE 802.11a (and 802.11n) standard as an example. The proposed receiver is based on an iterative joint source-channel decoding approach. The Soft-Input Soft-Output outer source decoder is based on a sequential M-algorithm, which has been modified to improve the decoding performance by exploiting the specific grammatical and syntax rules of (i) Huffman codes; (ii) Lempel-Ziv codes; and (iii) HTML language. Simulation results following the IEEE 802.11a (and 802.11n) standard over additive white Gaussian noise and Rayleigh fading channels show that the proposed receiver drastically reduces the number of errors occurring in the received HTML files compared to the classical receivers. An EXIT chart analysis illustrates some properties of this combination of source and channel decoders

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