Well adapted to the loosely coupled nature of distributed interaction in large-scale applications, the publish/subscribe communication paradigm has recently received increasing attention. With systems based on the publish/subscribe interaction scheme, subscribers register their interest in an event, or a pattern of events, and are subsequently asynchronously notified of events generated by publishers. Many variants of the paradigm have recently been proposed, each variant being specifically adapted to some given application or network model. This paper factors out the common denominator underlying these variants: full decoupling of the communicating entities in time, space, and synchronization. We use these three decoupling dimensions to better identify commonalities and divergences with traditional interaction paradigms. The many variations on the theme of publish/subscribe are classified and synthesized. In particular, their respective benefits and shortcomings are discussed both in terms of interfaces and implementations.

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The many faces of publish/subscribe

In this paper, we argue that there is a need for an event-based middleware to build large-scale distributed systems. Existing publish/subscribe systems still have limitations compared to invocation-based middlewares. We introduce Hermes, a novel event-based distributed middleware architecture that follows a type- and attribute-based publish/subscribe model. It centres around the notion of an event type and supports features commonly known from object-oriented languages like type hierarchies and super-type subscriptions. A scalable routing algorithm using an overlay routing network is presented that avoids global broadcasts by creating rendezvous nodes. Fault-tolerance mechanisms that can cope with different kinds of failures in the middleware are integrated with the routing algorithm resulting in a scalable and robust system.

/pdf/hermes-a-distributed-event-based-middleware-architecture-8hs2a1bxpa.pdf

Hermes: a distributed event-based middleware architecture

The CORBA Event Service provides a flexible model for asynchronous communication among objects. However, the standard CORBA Event Service specification lacks important features required by real-time applications. For instance, operational flight programs for fighter aircraft have complex real-time processing requirements. This paper describes the design and performance of an object-oriented, real-time implementation of the GORBA Event Service that is designed to meet these requirements.This paper makes three contributions to the design and performance measurement of object-oriented real-time systems. First, it illustrates how to extend the CORBA Event Service so that it is suitable for real-time systems. These extensions support periodic rate-based event processing and efficient event filtering and correlation. Second, it describes how to develop object-oriented event dispatching and scheduling mechanisms that can provide real-time guarantees. Finally, the paper presents benchmarks that demonstrate the performance tradeoffs of alternative concurrent dispatching mechanisms for real-time Event Services.

/pdf/the-design-and-performance-of-a-real-time-corba-event-3mtp4pvyua.pdf

The design and performance of a real-time CORBA event service

Cooperative Information Systems (CoopIS) 2004 International Conference- CoopIS 2004 International Conference (International Conference on Cooperative Information Systems) PC Co-chairs' Message- Keynote- Business Process Optimization- Workflow/Process/Web Services, I- Discovering Workflow Transactional Behavior from Event-Based Log- A Flexible Mediation Process for Large Distributed Information Systems- Exception Handling Through a Workflow- Workflow/Process/Web Services, II- A Flexible and Composite Schema Matching Algorithm- Analysis, Transformation, and Improvements of ebXML Choreographies Based on Workflow Patterns- The Notion of Business Process Revisited- Workflow/Process/Web Services, III- Disjoint and Overlapping Process Changes: Challenges, Solutions, Applications- Untangling Unstructured Cyclic Flows - A Solution Based on Continuations- Making Workflow Models Sound Using Petri Net Controller Synthesis- Database Management/Transaction- Concurrent Undo Operations in Collaborative Environments Using Operational Transformation- Refresco: Improving Query Performance Through Freshness Control in a Database Cluster- Automated Supervision of Data Production - Managing the Creation of Statistical Reports on Periodic Data- Schema Integration/Agents- Deriving Sub-schema Similarities from Semantically Heterogeneous XML Sources- Supporting Similarity Operations Based on Approximate String Matching on the Web- Managing Semantic Compensation in a Multi-agent System- Modelling with Ubiquitous Agents a Web-Based Information System Accessed Through Mobile Devices- Events- A Meta-service for Event Notification- Classification and Analysis of Distributed Event Filtering Algorithms- P2P/Collaboration- A Collaborative Model for Agricultural Supply Chains- FairNet - How to Counter Free Riding in Peer-to-Peer Data Structures- Supporting Collaborative Layouting in Word Processing- A Reliable Content-Based Routing Protocol over Structured Peer-to-Peer Networks- Applications, I- Covering Your Back: Intelligent Virtual Agents in Humanitarian Missions Providing Mutual Support- Dynamic Modelling of Demand Driven Value Networks- An E-marketplace for Auctions and Negotiations in the Constructions Sector- Applications, II- Managing Changes to Engineering Products Through the Co-ordination of Human and Technical Activities- Towards Automatic Deployment in eHome Systems: Description Language and Tool Support- A Prototype of a Context-Based Architecture for Intelligent Home Environments- Trust/Security/Contracts- Trust-Aware Collaborative Filtering for Recommender Systems- Service Graphs for Building Trust- Detecting Violators of Multi-party Contracts- Potpourri- Leadership Maintenance in Group-Based Location Management Scheme- TLS: A Tree-Based DHT Lookup Service for Highly Dynamic Networks- Minimizing the Network Distance in Distributed Web Crawling- Ontologies, DataBases, and Applications of Semantics (ODBASE) 2004 International Conference- ODBASE 2004 International Conference (Ontologies, DataBases, and Applications of Semantics) PC Co-chairs' Message- Keynote- Helping People (and Machines) Understanding Each Other: The Role of Formal Ontology- Knowledge Extraction- Automatic Initiation of an Ontology- Knowledge Extraction from Classification Schemas- Semantic Web in Practice- Generation and Management of a Medical Ontology in a Semantic Web Retrieval System- Semantic Web Based Content Enrichment and Knowledge Reuse in E-science- The Role of Foundational Ontologies in Manufacturing Domain Applications- Intellectual Property Rights Management Using a Semantic Web Information System- Ontologies and IR- Intelligent Retrieval of Digital Resources by Exploiting Their Semantic Context- The Chrysostom Knowledge Base: An Ontology of Historical Interactions- Text Simplification for Information-Seeking Applications- Information Integration- Integration of Integrity Constraints in Federated Schemata Based on Tight Constraining- Modal Query Language for Databases with Partial Orders- Composing Mappings Between Schemas Using a Reference Ontology- Assisting Ontology Integration with Existing Thesauri

On the move to meaningful Internet systems 2004 : CoopIS, DOA, and ODBASE : OTM confederated international conferences, CoopIS, DOA, and ODBASE 2004, Agia Napa, Cyprus, October 25-29, 2004 : proceedings (part II)

OASIS is a role-based access control architecture for achieving secure interoperation of services in an open, distributed environment. The aim of OASIS is to allow autonomous management domains to specify their own access control policies and to interoperate subject to service level agreements (SLAs). Services define roles and implement formally specified policy to control role activation and service use; users must present the required credentials, in an appropriate context, in order to activate a role or invoke a service. All privileges are derived from roles, which are activated for the duration of a session only. In addition, a role is deactivated immediately if any of the conditions of the membership rule associated with its activation becomes false. These conditions can test the context, thus ensuring active monitoring of security.To support the management of privileges, OASIS introduces appointment. Users in certain roles are authorized to issue other users with appointment certificates, which may be a prerequisite for activating one or more roles. The conditions for activating a role at a service may include appointment certificates as well as prerequisite roles and constraints on the context. An appointment certificate does not therefore convey privileges directly but can be used as a credential for role activation. The lifetime of appointment certificates is not restricted to the issuing session, so they can be used as long-lived credentials to represent academic and professional qualification, or membership of an organization.Role-based access control (RBAC), in associating privileges with roles, provides a means of expressing access control that is scalable to large numbers of principals. However, pure RBAC associates privileges only with roles, whereas applications often require more fine-grained access control. Parametrized roles extend the functionality to meet this need.We motivate our approach and formalise OASIS. We first present the overall architecture through a basic model, followed by an extended model that includes parametrization.

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A model of OASIS role-based access control and its support for active security

In the late 1980s, software designers introduced middleware platforms to support distributed computing systems. Since then, the rapid evolution of technology has caused an explosion of distributed-processing requirements. Application developers now routinely expect to support multimedia systems and mobile users and computers. Timely response to asynchronous events is crucial to such applications, but current platforms do not adequately meet this need. Another need of existing and emerging applications is the secure interoperability of independent services in large-scale, widely distributed systems. Information systems serving organizations such as universities, hospitals, and government agencies require cross-domain interaction. To meet the needs of these applications, Cambridge University researchers developed middleware extensions that provide a flexible, scalable approach to distributed-application development. This article details the extensions they developed, explaining their distributed software approach and the support it has provided for emerging applications.

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Generic support for distributed applications

Events are an emerging paradigm for composing applications in an open, heterogeneous distributed world. In Cambridge we have developed scalable event handling based on a publish-register-notify model with event object classes and server-side filtering based on parameter templates. After experience in using this approach in a home-built RPC system we have extended CORBA, an open standard for distributed object computing, to handle events in this way.

In this paper, we present the design of COBEA - a COrba-Based Event Architecture. A service that is the source of (parameterised) events publishes in a Trader the events it is prepared to notify, along with its normal interface specification. For scalability, a client must register interest (by invoking a register method with appropriate parameters or wild cards) at the service, at which point an access control check is carried out. Subsequently, whenever a matching event occurs, the client is notified.

We outline the requirements on the COBEA architecture, then describe its components and their interfaces. The design and implementation aim to support easy construction of applications by using COBEA components. The components include event primitives, an event mediator and a composite event service; each features well-defined interfaces and semantics for event registration, notification and filtering. We demonstrate that COBEA is flexible in supporting various application scenarios yet handles efficiently the most common event communications. The performance of server-side filtering for various registration scenarios is presented. Our initial experience with applications is also described.

/pdf/cobea-a-corba-based-event-architecture-4hdlz99zav.pdf

COBEA: a CORBA-based event architecture

The Cambridge Event Architecture has added events to an object-oriented, distributed programming environment by using a language independent interface definition language to specify and publish event classes. Here we present an extension to CEA using the ODMG standard, which unifies the transmission and storage of events. We extend the existing model with an ODL parser, an event stub generator, a metadata repository and an event library supporting both C++ and Java. The ODMG metadata interface allows clients to interrogate the system at run time to determine the interface specifications for subsequent event registration. This allows new objects to be added to a running system and independently developed components to interwork with minimum prior agreement. Traditional name services and interface traders can be defined more generally using object database schemas. Type hierarchies may be used in schemas. Matching at a higher level in the type hierarchy for different domains is possible even though different specialisations are used in individual domains. Using metadata to describe events provides the basis for establishing contracts between domains. These are used to construct the event translation layer between heterogeneous domains.

Event Storage and Federation Using ODMG

Web services based systems have recently found their way into many applications such as e-commerce, corporate integration and e-learning. Construction of new services or introducing new functions to existing services requires composition of web services. Current approaches to service composition often require major programming effort; this is time consuming and requires considerable developer expertise. In this paper, we explore the real and rich scenarios found in e-learning where education services are offered through the Internet by networked universities to potentially millions in the world. These services are derived from existing/emerging business operation processes and commonly offered through a web interface, combined with other services such as email and ftp services, to support partial/full business processes. We identify the requirements for a generic portal framework for easy integration of existing expertise and services of individual institutions (enterprises). We examine the existing technologies and standards, and point out the gaps to be filled in designing the architecture of the framework.

Towards the Design of a Portal Framework for Web Services Integration

A cross-domain workflow application may be constructed using a standard reference model such as the one by the Workflow Management Coalition (WfMC) [7] but the requirements for this type of application are inherently different from one organization to another. The existing models and systems built around them meet some but not all the requirements from all the organizations involved in a collaborative process. Furthermore the requirements change over time. This makes the applications difficult to develop and distribute. Service Oriented Architecture (SOA) based approaches such as the BPET (Business Process Execution Language) intend to provide a solution but fail to address the problems sufficiently, especially in the situations where the expectations and level of skills of the users (e.g. the participants of the processes) in different organisations are likely to be different. In this paper, we discuss a design pattern that provides a novel approach towards a solution. In the solution, business users can design the applications at a high level of abstraction: the use cases and user interactions; the designs are documented and used, together with the data and events captured later that represents the user interactions with the systems, to feed an intermediate component local to the users -the IFM (InterFace Mapper) -which bridges the gaps between the users and the systems. We discuss the main issues faced in the design and prototyping. The approach alleviates the need for re-programming with the APIs to any back-end service thus easing the development and distribution of the applications.

Chaoying Ma

Papers

Generic support for distributed applications

COBEA: a CORBA-based event architecture

Event Storage and Federation Using ODMG

Towards the Design of a Portal Framework for Web Services Integration

A Design Pattern for Integration of Business Process Management Systems