Milliam Maxime Zekeng Ndadji

Milliam Maxime Zekeng Ndadji

Simulation is an indispensable tool for validating distributed IoT architectures before physical deployment, and iFogSim has emerged as one of the most widely adopted platform in the fog and edge computing research community. Yet the experience of using iFogSim for non-canonical, application-specific architectures remains incompletely documented, leaving practitioners without guidance on when the tool is appropriate, which scientific objectives it can address, and how to manage the modelling approximations it imposes. This article helps in providing that guidance through two complementary contributions. First, we present a structured state of the art covering iFogSim and iFogSim2, a taxonomy of ten scientific objectives that motivate IoT architecture simulation, and a comparative survey of eight simulation tools assessed against those objectives. Second, we report our experience of simulating a four-tier smart emergency response system for resource-constrained urban environments, covering a 25-node synthetic road topology, four experimental configurations, and quantitative results including end-to-end alert latency (near 205 ms), FPGA-accelerated Dijkstra path computation (x10 CPU speedup), concurrent incident conflict rates (75% under dual load), and path-cache acceleration (x197). The analysis is organised around five practitioner questions: whether iFogSim fits the target architecture, which objectives it covers natively versus partially, what modelling challenges arise and how their workarounds bias reported results, what changes to the iFogSim source code would close the identified gaps, and whether tool co-simulation can provide comprehensive coverage. Seven modelling challenges are documented with source-code-grounded root causes and explicit bias assessments; finally, seven developer recommendations are proposed as an actionable improvement roadmap for the iFogSim community.

Milliam Maxime Zekeng Ndadji

In this thesis, we focus on the proposal of distributed workflow systems dedicated to the automation of administrative business processes. We propose an approach to build such systems by relying on the concepts of multiagent systems, Peer to Peer (P2P) architecture, Service-Oriented Architecture (SOA) and structured documents (artifacts) cooperative edition. Indeed, we develop mathematical tools that allow any workflow systems designer, to express each administrative process in the form of an attributed grammar whose symbols represent tasks to be executed, productions specify a scheduling of these tasks, and instances (the derivation trees that conform to it) represent the different execution scenarios leading to business goal states. The obtained grammatical model is then introduced into a proposed P2P system which is in charge of carrying out the completely decentralised execution of the underlying process's instances. The said system orchestrates a process's instance execution as a choreography during which, various software agents driven by human agents (actors), coordinate themselves through artifacts that they collectively edit. The exchanged artifacts represent the system's memory: they provide information on already executed tasks, on those ready to be executed and on their executors. The software agents are autonomous and identical: they execute the same unique protocol each time they receive an artifact. This protocol allows them to identify the tasks they must immediately execute, to execute them, to update the artifact and to disseminate it if necessary, for the continuation of the execution. Moreover, actors potentially have only a partial perception of processes in which they are involved. In practice, this means that certain tasks can be carried out confidentially.

Milliam Maxime Zekeng Ndadji, Maurice Tchoupé Tchendji, Clémentin Tayou Djamegni et al.

During the last two decades, the decentralized execution of business processes has been one of the main research topics in Business Process Management. Several models (languages) for processes' specification in order to facilitate their distributed execution, have been proposed. LSAWfP is among the most recent in this area: it helps to specify administrative processes with grammatical models indicating, in addition to their fundamental elements, the permissions (reading, writing and execution) of each actor in relation to each of their tasks. In this paper, we present a model for a completely decentralized and artifact-centric execution of administrative processes specified using LSAWfP. The presented model puts particular emphasis on actors' views: it then allows the confidential execution of certain tasks by ensuring that, each actor potentially has only a partial perception of the processes' global execution states. The model thus solves a very important problem in business process execution, which is often sidelined in existing approaches. To accomplish this, the model rely on three projection algorithms allowing to partially replicate the processes' global execution states at a given moment, to consistently update the obtained partial states and to deduce new coherent global states. The proposal of these three algorithms, the proof of underlying mathematical tools' stability and a proposal of their implementation, are this paper's main contributions.

Milliam Maxime Zekeng Ndadji, Maurice Tchoupé Tchendji, Clémentin Tayou Djamegni et al.

In Business Process Management (BPM), process modelling has been solved in various ways. However, there are no commonly accepted modelling tools (languages). Some of them are criticized for their inability to capture both the lifecycle, informational and organizational models of processes. For some others, process modelling is generally done using a single graph; this does not facilitate modularity, maintenance and scalability. In addition, some of these languages are very general; hence, their application to specific domain processes (such as administrative processes) is very complex. In this paper, we present a new language and a new methodology, dedicated to administrative process modelling. This language is based on a variant of attributed grammars and is able to capture the lifecycle, informational and organizational models of such processes. Also, it proposes a simple graphical formalism allowing to model each process's execution scenario as an annotated tree (modularity). In the new language, a particular emphasis is put on modelling (using "views") the perceptions that actors have on processes and their data.

Maurice Tchoupé Tchendji, Milliam Maxime Zekeng Ndadji

In an asynchronous cooperative editing workflow of a structured document, each of the co-authors receives in the different phases of the editing process, a copy of the document to insert its contribution. For confidentiality reasons, this copy may be only a partial replica containing only parts of the (global) document which are of demonstrated interest for the considered co-author. Note that some parts may be a demonstrated interest over a co-author; they will therefore be accessible concurrently. When it's synchronization time (e.g. at the end of an asynchronous editing phase of the process), we want to merge all contributions of all authors in a single document. Due to the asynchronism of edition and to the potential existence of the document parts offering concurrent access, conflicts may arise and make partial replicas unmergeable in their entirety: they are inconsistent, meaning that they contain conflictual parts. The purpose of this paper is to propose a merging approach said by consensus of such partial replicas using tree automata. Specifically, from the partial replicas updates, we build a tree automaton that accepts exactly the consensus documents. These documents are the maximum prefixes containing no conflict of partial replicas merged.