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Rachid Hamadi

The University of New South Wales, School of Computer Science and Engineering, Faculty Member

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I am a Senior Lecturer at the School of Computer Science and Engineering (CSE) at the University of New South Wales (UNSW). I received my Ph.D. in Computer Science and Engineering from UNSW. I also hold a M.Sc. and a B.Sc. (with Honours) both in Computer Science from the University of Science and Technology Houari Boumediene (USTHB), Algeria. Prior to joining UNSW, I held Lecturer positions at Federation University, Victoria University, University of New England, Central Queensland University, and USTHB (Algeria).

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Papers by Rachid Hamadi

From Service-Oriented Computing to Metaverse Services: A Framework for Inclusive and Immersive Learning for Neurodivergent Students

arXiv preprint arXiv:2509.15545, 2025

The metaverse offers immersive and adaptive learning environments for neurodivergent students to ... more The metaverse offers immersive and adaptive learning environments for neurodivergent students to thrive and reach their full potential. In this paper, we propose a generic framework that leverages metaverse services as an evolution beyond traditional service-oriented computing, enabling more interactive, personalized, and engaging educational experiences. By integrating AI-driven adaptability, multimodal interaction, and privacy-first service design, the framework ensures that learning remains accessible, inclusive, and secure. Additionally, we explore the challenges associated with scalability, data privacy, and ethical considerations while highlighting opportunities for fostering safe and student-centered virtual spaces. Our analysis underscores the potential of metaverse-based learning to bridge accessibility gaps, support social-emotional development, and empower neurodivergent learners in both digital and realworld settings. We also provide recommendations and policy considerations for creating a secure, inclusive, and scalable metaverse learning ecosystem for neurodivergent students.

A Top-Down Petri Net-Based Approach for Dynamic Workflow Modeling

Lecture Notes in Computer Science, 2003

A top-down approach for workflow design is proposed in the framework of Petri net theory. Simple ... more A top-down approach for workflow design is proposed in the framework of Petri net theory. Simple but powerful refinement rules are proposed that guarantee soundness of the resulting workflow nets. The refinement process supports the definition of regions, which are parts of the workflow that correspond to logistically related items. Exception handlers can be associated to regions. Defining regions helps determining the impact areas of the unexpected events during workflow execution.

A Petri Net-based Hierarchical Workflow Designer

Recovery Nets: Towards Self-Adaptive Workfow Systems

A workflow management system (WfMS) provides a central control point for defining business proces... more A workflow management system (WfMS) provides a central control point for defining business processes and orchestrating their execution. A major limitation of current WfMSs is their lack of support for dynamic workflow adaptations. This functionality is an important requirement in order to provide sufficient flexibility to cope with expected but unusual situations and failures. In this paper, we propose Self-Adaptive Recovery Net (SARN), an extended Petri net model for specifying exceptional behavior in workflow systems at design time. SARN can adapt the structure of the underlying Petri net at run time to handle exceptions while keeping the Petri net design simple and easy. The proposed framework also caters for high-level recovery policies that are incorporated either with a single task or a set of tasks, called a recovery region.

HiWorD: a Petri net-based hierarchical workflow designer

Third International Conference on Application of Concurrency to System Design, 2003. Proceedings., 2003

Much work is being conducted in the area of business process modeling using workflow technology. ... more Much work is being conducted in the area of business process modeling using workflow technology. HiWorD is a hierarchical workflow modeling prototype with simulation capability. It models business processes using Petri nets in a hierarchical manner and implements recovery transitions as a technique to recover from exceptions. The workflow hierarchy is created by refining places and transitions using predefined patterns. By using these patterns, it is proven that the resulting workflow will be sound.

Modèles du vrai parallélisme et bisimulations avant arrière

Master's Thesis, 1995

Ce travail entre dans le cadre de l'étude des modèles non-séquentiels du parallélisme, souvent qu... more Ce travail entre dans le cadre de l'étude des modèles non-séquentiels du parallélisme, souvent qualifiés de modèles du vrai parallélisme car ils considèrent la notion de parallélisme comme fondamentale. Les modèles non-séquentiels typiques sont les réseaux de Petri et les structures
d'événements. L'autre approche standard est appelée approche d'entrelacement parce qu'elle réduit le parallélisme à la séquentialité et au non-déterminisme. Les systèmes de transitions en sont un modèle
typique.
Après une étude des principaux modèles du parallélisme et des équivalences comportementales de bisimulation qui leur sont associées, nous proposons deux sémantiques pour l'algèbre de processus CCS à l'aide des réseaux de Petri. La première est une sémantique dénotationnelle (compositionnelle) où les opérations sémantiques sont définies explicitement sur des réseaux de Petri et la seconde est une
sémantique opérationnelle structurée utilisant les règles de transition "à la Plotkin". Nous montrons que ces deux interprétations de CCS peuvent coïncider, en ce sens que les parties atteignables des deux
réseaux de Petri associés à un terme CCS fini sont isomorphes.
Nous nous intéressons ensuite particulièrement à l'équivalence de bisimulation avant-arrière, une variante de la bisimulation classique ou la propriété de transfert est vérifiée non seulement en avant mais aussi en arrière. Ainsi, nous présentons et comparons les deux notions différentes de bisimulation avant-arrière sur les structures d'événements premières proposées dans la littérature.
Enfin, nous définissons la notion de bisimulation avant-arrière sur les réseaux de Petri en présence des actions invisibles et comparons ces nouvelles équivalences aux bisimulations ordinaires. Nous montrons principalement que les versions avant-arrière de la "concurrent" bisimulation et de la "fully concurrent" bisimulation coïncident ct qu'elles sont plus fines que leur version avant. De plus, nous étudions le comportement des équivalences introduites vis-à-vis du raffinement d'actions.

HiWorD: A Petri Net-Based Hierarchical Workflow Designer

Third International Conference on Application of Concurrency to System Design, 2003

Much work is being conducted in the area of business process modeling using workflow technology. ... more Much work is being conducted in the area of business process modeling using workflow technology. HiWorD is a hierarchical workflow modeling prototype with simulation capability. It models business processes using Petri nets in a hierarchical manner and implements recovery transitions as a technique to recover from exceptions. The workflow hierarchy is created by refining places and transitions using predefined patterns. By using these patterns, it is proven that the resulting workflow will be sound.

A top-down petri net-based approach for dynamic workflow modeling

by Rachid Hamadi and Piotr Chrzastowski-Wachtel

Business Process Management: International Conference, BPM 2003 Eindhoven, The Netherlands, Jun 2003

A top-down approach for workflow design is proposed in the framework of Petri net theory. Simple ... more A top-down approach for workflow design is proposed in the framework of Petri net theory. Simple but powerful refinement rules are proposed that guarantee soundness of the resulting workflow nets. The refinement process supports the definition of regions, which are parts of the workflow that correspond to logistically related items. Exception handlers can be associated to regions. Defining regions helps determining the impact areas of the unexpected events during workflow execution.

Formal composition and recovery policies in service-based business processes

PhD Thesis, 2005

Process-based composition of Web services is emerging as a promising tech- nology for the eﬀect... more Process-based composition of Web services is emerging as a promising tech-
nology for the eﬀective automation of integrated and collaborative applica-
tions. As Web services are often autonomous and heterogeneous entities,
coordinating their interactions to build complex processes is a diﬃcult, er-
ror prone, and time-consuming task. In addition, since Web services usually
operate in dynamic and highly evolving environments, there is a need for sup-
porting ﬂexible and correct execution of integrated processes. In this thesis,
we propose a Petri net-based framework for formal composition and recovery
policies in service-based business processes. We ﬁrst propose an algebra for
composing Web services. The formal semantics of this algebra is expressed in
terms of Petri nets. The use of a formal model allows the eﬀective veriﬁcation
and analysis of properties, both within a service, such as termination and ab-
sence of deadlock, and between services, such as behavioral equivalences. We
also develop a top-down approach for the correct (e.g., absence of deadlock
and termination) composition of complex business processes. The proposed
approach deﬁnes a set of reﬁnement operators that guarantee correctness of
the resulting business process nets at design time. We then introduce Self-
Adaptive Recovery Net (SARN), an extended Petri net model for specifying
exceptional behavior in business processes. SARN adapts the structure of the
underlying Petri net at run time to handle exceptions while keeping the Petri
net design simple and easy. The proposed framework caters for the speciﬁca-
tion of high-level recovery policies that are incorporated either with a single
task or a set of tasks, called a recovery region. Finally, we propose a pattern-
based approach to dynamically restructure SARN. These patterns capture
the ways past exceptions have been dealt with. The objective is to con-
tinuously restructure recovery regions within the SARN model to minimize
the impact of exception handling. To illustrate the viability of the proposed
composition and exception handling techniques, we have developed HiWorD
(HIerarchical WORkﬂow Designer), a hierarchical Petri net-based business
process modeling and simulation tool.

Conceptual Modeling of Web Service Conversations

Lecture Notes in Computer Science, 2003

Web services are emerging as a promising technology for the effective automation of inter-organiz... more Web services are emerging as a promising technology for the effective automation of inter-organizational interactions. Several standards that aim at providing infrastructure to support Web services description, discovery, and composition have recently emerged including WSDL, UDDI, and BPEL4WS. Indeed, advances in this area promise to take cross-organizational application integration a step further by facilitating the automatic discovery and invocation of relevant services. However, despite the growing interest in Web services, several issues still need to be addressed to provide similar benefits to what traditional middleware brings to intra-organizational application integration (e.g., transaction support). In this paper, we identify a framework for defining extended service models to enable the definition of richer Web service abstractions. We also identify and define specific abstractions based on an analysis of existing e-commerce Web portals. Finally, we show how the model and the abstractions are supported by a conversation manager implemented on top of the SELF-SERV platform.

Usage—Centric Adaptation of Dynamic E—Catalogs

by Rachid Hamadi and Hye-young Paik

Lecture Notes in Computer Science, 2002

Although research into the integration of e-catalogs has gained considerable momentum over the ye... more Although research into the integration of e-catalogs has gained considerable momentum over the years, the needs for building adaptive catalogs have been largely ignored. Catalogs are designed by system designers who have a priori expectations for how catalogs will be explored by users. It is necessary to consider how users are using catalogs since they may have different expectations. In this paper, we describe the design and the implementation of a system through which integrated product catalogs are continuously adapted and restructured within a dynamic environment. The adaptation of integrated catalogs is based on the observation of customers' interaction patterns.

Conceptual Modeling of Privacy-Aware Web Service Protocols

Lecture Notes in Computer Science, 2007

Internet users are becoming increasingly concerned about their personal information being collect... more Internet users are becoming increasingly concerned about their personal information being collected and used by Web service providers. They want to ensure that it is stored and used according to the providers' privacy policies. Since these policies are mainly developed and maintained separately from the business process that collects and manipulates data, it is hard to perform analysis and management of the processes in terms of privacy policies. To address this problem, we propose a formal technique with which Web service providers describe the use and storage of personal data. The description is integrated with a Web service protocol using an extended state machine model. Having such a conceptual model will enable model-driven development and management of Web service protocols with respect to their privacy aspects such as collection, disclosure, and obligation. A tool support has been implemented, as part of ServiceMosaic, to let designers model privacy aspects within the Web service protocol.

Recovery Nets: Towards Self-Adaptive Workflow Systems

Lecture Notes in Computer Science, 2004

A workflow management system (WfMS) provides a central control point for defining business proces... more A workflow management system (WfMS) provides a central control point for defining business processes and orchestrating their execution. A major limitation of current WfMSs is their lack of support for dynamic workflow adaptations. This functionality is an important requirement in order to provide sufficient flexibility to cope with expected but unusual situations and failures. In this paper, we propose Self-Adaptive Recovery Net (SARN), an extended Petri net model for specifying exceptional behavior in workflow systems at design time. SARN can adapt the structure of the underlying Petri net at run time to handle exceptions while keeping the Petri net design simple and easy. The proposed framework also caters for high-level recovery policies that are incorporated either with a single task or a set of tasks, called a recovery region.

Self-adapting recovery nets for policy-driven exception handling in business processes

Distributed and Parallel Databases, 2008

In this paper, we propose Self-Adapting Recovery Net (SARN), an extended Petri net model, for spe... more In this paper, we propose Self-Adapting Recovery Net (SARN), an extended Petri net model, for specifying exceptional behavior in business processes. SARN adapts the structure of the underlying Petri net at run time to handle exceptions while keeping the Petri net design easy. The proposed framework caters for the specification of high-level recovery policies that are incorporated either with a single task or a set of tasks, called a Recovery Region. These recovery policies are generic directives that model exceptions at design time together with a set of primitive operations used at run time to handle the occurrence of exceptions. We identified a set of recovery policies that are useful and commonly needed in many practical situations. A tool has been developed to illustrate the viability of the proposed exception handling technique.

Dynamic restructuring of recovery nets

Proceedings of the 16th Australasian database conference, 2005

A Self-Adaptive Recovery Net (SARN) is an extended Petri net model for specifying exceptional beh... more A Self-Adaptive Recovery Net (SARN) is an extended Petri net model for specifying exceptional behavior in workflow systems. SARN caters for high-level recovery policies that are incorporated either with a single task or a set of tasks, called a recovery region. A recovery region delimits the part of the workflow from which the associated recovery policies take place. In this paper, we assume that SARN is initially partitioned into recovery regions by workflow designers who have a priori expectations for how exceptions will be handled. We propose a pattern-based approach to dynamically restructure SARN partition. The objective is to continuously restructure recovery regions within SARN partition to reflect the dynamic changes in handling exceptions. The restructuring of SARN partition is based on the observation of predefined recovery patterns.

Policy-based Exception Handling in Business Processes

Technical Report, 2004

A workflow management system (WfMS) provides a central control point for defining business proces... more A workflow management system (WfMS) provides a central control point for defining business processes and orchestrating their execution. A major limitation of current WfMSs is their lack of support for dynamic workflow adaptations. This functionality is an important requirement in order to provide sufficient flexibility to cope with expected but unusual situations and failures. In this report, we propose Self-Adaptive Recovery Net (SARN), an extended Petri net model for specifying exceptional behavior in workflow systems at design time. SARN can adapt the structure of the underlying Petri net at run time to handle exceptions while keeping the Petri net design simple and easy. The proposed framework also caters for high-level recovery policies that are incorporated either with a single task or a set of tasks, called a recovery region. These recovery policies are generic constructs that model exceptions at design time together with a set of primitive operations that can be used at run time to handle the occurrence of exceptions.

Dynamic restructuring of e-catalog communities based on user interaction patterns

World Wide Web, 2002

Since e-catalogs are dynamic, autonomous, and heterogeneous, the integration of a potentially lar... more Since e-catalogs are dynamic, autonomous, and heterogeneous, the integration of a potentially large number of dynamic e-catalogs is a delicate and time-consuming task. In this paper, we describe the design and the implementation of a system through which existing on-line product catalogs can be integrated, and the resulting integrated catalogs can be continuously adapted and personalized within a dynamic environment. The integration framework originates from a previous project on integration of Web data, called WebFINDIT. Using the framework, we propose a methodology for adaptation of integrated catalogs based on the observation of customers' interaction patterns.

A Petri net-based model for web service composition

Proceedings of the 14th Australasian database conference - Volume 17, 2003

The Internet is going through several major changes. It has become a vehicle of Web services rath... more The Internet is going through several major changes. It has become a vehicle of Web services rather than just a repository of information. Many organizations are putting their core business competencies on the Internet as a collection of Web services. An important challenge is to integrate them to create new value-added Web services in ways that could never be foreseen forming what is known as Business-to-Business (B2B) services. Therefore, there is a need for modeling techniques and tools for reliable Web service composition. In this paper, we propose a Petri net-based algebra, used to model control flows, as a necessary constituent of reliable Web service composition process. This algebra is expressive enough to capture the semantics of complex Web service combinations.