Département Informatique

Computer Science Department of Telecom SudParis

New paper “Process mining approach for multi-cloud SLA reporting” at IEEE Big Data 2023

Authors: Jeremy Mechouche, Mohamed Sellami, Zakaria Maamar, Roua Touihri, and Walid Gaaloul

Abstract

Cloud consumers’ requirements possess an inherent dynamic nature, characterized by fluctuating needs in reliability and high-availability relative to their workload. To satisfy these requirements, service reconfiguration strategies are put in place ensuring first, adaptable service provisioning and second, compliance with the agreed-upon Service Level Agreements (SLAs) between consumers and providers. However, deviations between SLAs and “real” observed behaviours could occur even after triggering reconfiguration strategies. Additionally, as organizations increasingly embrace multi-cloud environments, careful consideration must be given to the inherent challenges that arise in this requirements satisfaction. In this paper, we represent these strategies as state machines used to report their conformance to collected logs which track what really happened at run-time. The collected logs are processed to construct state machines suitable for conformance checking. Experiments demonstrating the technical doability of using conformance checking to detect deviations between SLAs and logs, along with verifying the suitability of reconfiguration strategies, are also discussed in the paper.

New paper “Uncovering Implicit Bundling Constraints: Empowering Cloud Network Service Discovery” at ICSOC 2023

Authors: Hayet Brabra, Imen Jerbi, Mohamed Sellami, Walid Gaaloul, and Djamal Zeghlache

Abstract

Cloud service providers (CSPs) offer their networking services (NSs) in the form of service bundles containing underlying services, not necessarily requested by the users. While service bundling is a common practice in the cloud providing multiple components as a single service, unawareness of this hidden structure of services at design time may limit their portability, compatibility, and interoperability across multiple providers. This calls for service discovery solutions that can identify and reveal such hidden bundling to cloud users so they become aware of the consequences of existing bundling before any deployment stage. This paper presents a new NSs discovery approach that takes into account and makes transparent network services bundling for cloud users.

New paper “Discovering Guard Stage Milestone Models Through Hierarchical Clustering” at CoopIS 2023

Authors: Leyla Moctar M’Baba, Mohamed Sellami, Nour Assy, Walid Gaaloul, and Mohamedade Farouk Nanne

Abstract

Processes executed on enterprise Information Systems (IS), such as ERP and CMS, are artifact-centric. The execution of these processes is driven by the creation and evolution of business entities called artifacts. Several artifact-centric modeling languages were proposed to capture the specificity of these processes. One of the most used artifact-centric modeling languages is the Guard Stage Milestone (GSM) language. It represents an artifact-centric process as an information model and a lifecycle. The lifecycle groups activities in stages with data conditions as guards. The hierarchy between the stages is based on common conditions. However, existing works do not discover this hierarchy nor the data conditions, as they considered them to be already available. They also do not discover GSM models directly from event logs. They discover Petri nets and translate them into GSM models. To fill this gap, we propose in this paper a discovery approach based on hierarchical clustering. We use invariants detection to discover data conditions and information gain of common conditions to cluster stages. The approach does not rely on domain knowledge nor translation mechanisms. It was implemented and evaluated using a blockchain case study.

New paper “Request relaxation based-on provider constraints for a capability-based NaaS services discovery” at CAISE 2023

Authors: Imen Jerbi, Hayet Brabra, Mohamed Sellami, Walid Gaaloul, Sami Bhiri, Boualem Benatallah, Djamal Zeghlache, and Olivier Tirat

Abstract

Network as a Service (NaaS) enables cloud customers to connect their distributed services across multiple clouds without relying exclusively on their infrastructures. The discovery of NaaS services remains challenging not only because of their scale and diversity but also because of the hidden constraints that cloud providers impose on these services at the networking layer. NaaS services are usually offered in the form of service bundles containing underlying services and constraints not requested by the customers. This creates undesirable dependencies and constraints that hamper portability, compatibility and interoperability across providers. The problem of service discovery becomes more challenging when these constraints are the main and first cause that prevents a customer’s request from being fulfilled. Without a mechanism that enables customers to identify these constraints and to adjust their requests accordingly, existing service discovery solutions are likely to fall short. We propose to complement existing service discovery solutions by not only identifying unmatched constraints but also recommending relaxing discovery requests to retrieve optimal and compliant services.

New article “Process mining for Artifact-Centric Blockchain Applications” in the SIMPAT journal

Authors: Leyla Moctar M’Baba, Nour Assy, Mohamed Sellami, Walid Gaaloul and Mohamedade Farouk NANNE

Abstract

Process mining can provide valuable insights into user behavior, performance, and security for blockchain applications. In return, process mining benefits from the trustworthiness of blockchain data. One obstacle to realizing these benefits is that blockchain data is inadequate for process mining. This issue has been previously explored in literature, but mainly with regards to workflow-centric processes, leaving out the more common artifact-centric applications. This article introduces ACEL (Artifact-Centric Event Log), an extension to the OCEL (Object-Centric Event Log) standard, specifically designed for artifact-centric processes. Additionally, we present a method for extracting ACEL logs from the Ethereum blockchain platform and demonstrate its effectiveness and the perspectives of process discovery through two case studies of public Ethereum applications.

New paper “Conformance checking for autonomous multi-cloud SLA management and adaptation” at Journal of Supercomputing

Authors: Jeremy Mechouche, Roua Touihri, Mohamed Sellami and Walid Gaaloul

Link: https://link.springer.com/article/10.1007/s11227-022-04363-0

Abstract

Satisfying cloud customers’ requirements, i.e., respecting an agreed-on service level agreement (SLA), is not a trivial task in a multi-cloud context. This is mainly due to divergent SLA objectives among the involved cloud service providers and hence divergent reconfiguration strategies to enforce them. In this paper, we propose a hierarchical representation of multi-cloud SLAs: sub-SLAs associated with a system’s components deployed on distinct cloud service providers and global-SLA associated with the whole system. We also enrich these SLA representations with state machines reflecting reconfiguration strategies defined by cloud customers. Then, we propose an autonomous multi-cloud resource orchestrator based on the MAPE-K adaptation control loop to enforce them and to avoid SLA violations. Finally, in order to check the conformity of this enforcement with defined multi-cloud SLA, we propose an approach for multi-cloud SLA reporting inspired by conformance checking techniques. An implementation of the approach is presented in the paper and illustrates the approach feasibility.

New paper “Trustworthy Cross-Organizational Collaborations with Hybrid On/Off-Chain Declarative Choreographies” at ICSOC’2021

Authors: Tiphaine Henry, Amina Brahem, Nassim Laga, Julien Hatin, Walid Gaaloul and Boualem Benatallah

Abstract

Business Process Management communities increasingly adopt the blockchain technology to support trustworthy decentralized execution of processes. In this context, the interest in business process choreographies rises as they offer a distributed way to compose and control cross-organizational processes. In choreographies, the process view is distributed between participants to limit privacy leakages. Hence, the process observability (i.e., who knows what) is challenging. On one side, partners have no insight into each other’s orchestration and communicate peer-to-peer via the public view. On the other side, they have to maintain their internal orchestrations’ states consistent with the choreography’s global state. The need to ensure a privacy-preserving method to enforce a blockchain-based execution thus rises. In the present work, we propose a unified solution for the hybrid on/off-chain generation and execution of business process choreographies. The public view, shared understanding of the cross-organizational process, is triggered by the on-chain smart contract. Participants generate their private views off-chain using this on-chain public view. They execute afterward the private views in their off-chain process execution engine. Our prototypical implementation demonstrates the feasibility of the approach .

New paper “Blockchain logging for process mining: a systematic review” at HICSS’2022

Authors: Leyla Moctar M’Baba, Mohamed Sellami, Walid Gaaloul and Mohamedade Farouk NANNE

Abstract

Considerable progress was forcasted for collaborative business processes with the rise of blockchain programmable platforms. One of the saliant promises was auditable traces of business process execution, but practically it has posed challenges specially with regard to blockchain logs’ structure who turned out to be inadequate for process mining techniques. Approaches to answer this issue have started to emerge in the literature; some focusing on the creation process of event logs, and others dealing with their retrieval from the blockchain. This work outlines the generic steps required to solve these challenges and analyzes findings in these approaches with a consideration for efficiency and future research directions.

New paper “Towards higher-level description of SLA-aware reconfiguration strategies based on state-machine” at ICEBE’2021

Authors: Jeremy Mechouche, Roua Touihri, Mohamed Sellami and Walid Gaaloul

Abstract

High number of European projects and international initiatives show an increased interest in the multi-cloud paradigm. One key need identified in these studies is an SLA-driven service model for multi-cloud environment. While offering a multi-cloud application, cloud consumer define reconfiguration strategies to avoid violating SLAs established with their customers. In this context, this paper presents an approach for enriching multi-cloud SLA representations with reconfiguration strategies. Advantages of this approach are twofold: (i) simplify SLA administration and (ii) limit SLA violations caused by reconfiguration strategies. We represent reconfiguration strategies based on state-machine formalism. Furthermore, we define thresholds to guarantee their compliance with multi-cloud SLAs and anticipate SLA violations. An implementation of the approach is presented in the paper and illustrates how these thresholds are computed.

New paper “A Transactional Approach to Enforce Resource Availabilities – Application to the Cloud” at RCIS’2021

Authors: Zakaria Maamar, Mohamed Sellami and Fatma Masmoudi

Abstract

This paper looks into the availability of resources, exemplified with the cloud, in an open and dynamic environment like the Internet. A growing number of users consume resources to complete their operations requiring a better way to manage these resources in order to avoid conflicts, for example. Resource availability is defined using a set of consumption properties (limited, limited-but-renewable, and non-shareable) and is enforced at run-time using a set of transactional properties (pivot, retriable, and compensatable). In this paper, a CloudSim-based system simulates how mixing consumption and transactional properties allows to capture users’ needs and requirements in terms of what cloud resources they need, for how long, and to what extent they tolerate the unavailability of these resources.