Amy Sundermier

Interconnection of distributed components: an overview of current middleware solutions

From design and manufacturing to electronic commerce, coordinating business activities in engineering applications requires accessing data and software from distributed sources. The Common Object Request Broker Architecture (CORBA) of the Object Management Group emerged in the 1990’s as a standard for access to distributed software components. Since that time, the standard has matured significantly, providing advanced features for event notification and transaction processing. At the same time, Javabased technology for distributed object computing has also emerged, from Remote Method Invocation to Enterprise JavaBeans, Jini Connection Technology, JavaSpaces, Java Messaging Service, and Java Transaction Service. Sorting through the options available for the use of such tools can be a difficult task. This paper provides an overview of CORBA and Java technology for distributed object computing. A comparison of these different technologies is presented, discussing the similarities and differences, as well as the way in which such tools can be used together for distributed access to the types of software and data components that are needed for the construction of distributed engineering applications. Future directions for the use of such tools are also identified.

Object Deltas in an Active Database Development Environment

Although the use of deltas in relational environments is fairly well established, the use of deltas in an object-oriented database (OODB) environment has not yet been fully explored. As OODBs continue to expand in functionality to include the use of active rules and integrity constraints, the need for object deltas becomes more apparent. This is especially true for active, object-oriented environments that also include deductive or declarative capabilities that are typically associated with relational systems. In this paper we present an object delta structure as an integral part of the architecture of an active database system. The object delta structure represents deltas as a natural extension to database objects through object-oriented concepts such as inheritance, encapsulation and abstraction. Object deltas are first-class objects that may be manipulated through a given set of behavior. The structure proposed goes beyond previous object delta definitions by representing incremental changes to arbitrarily complex data structures as part of the delta object. Object deltas are represented at different levels of granularity to better support the needs of different active system functions. We describe examples of using object deltas for condition monitoring and also for effective support of run-time testing and debugging tools.

Delta abstractions: A technique for managing database states in runtime debugging of active database rules

Delta abstractions are introduced as a mechanism for managing database states during the execution of active database rules. Delta abstractions build upon the use of object deltas, capturing changes to individual objects through a system-supported, collapsible type structure. The object delta structure is implemented using object-oriented concepts such as encapsulation and inheritance so that all database objects inherit the ability to transparently create and manage delta values. Delta abstractions provide an additional layer to the database programmer for organizing object deltas according to different language components that induce database changes, such as methods and active rules. As with object deltas, delta abstractions are transparently created and maintained by the active database system. We define different types of delta abstractions as views of object deltas and illustrate how the services of delta abstractions can be used to inspect the state of active rule execution. An active rule analysis and debugging tool has been implemented to demonstrate the use of object deltas and delta abstractions for dynamic analysis of active rules at runtime.

Component adaptation for event-based application integration using active rules

Enterprise applications integrate information and applications in a distributed, networked environment to develop a global application of interconnected components and applications. This paper presents the design and implementation of the wrappers generated to adapt components to a middleware environment that employs active rules to build an enterprise application using an event-driven approach to integrating distributed black-box components. The components adapted in this implementation are based on the Enterprise JavaBeans component model. An application integrator declares the components to be integrated, and may define additional attributes, relationships, and events to be used in the integration process. The metadata for the components to be integrated is used to adapt and enhance the black-box components through the use of wrappers. The wrappers act as a proxy to the black-box component. The adaptation of the wrappers provides for the storage of additional properties for component instances and for the detection of events within the components to generate event notifications. The wrappers are automatically generated from the component metadata using the Extensible Stylesheet Language. The design and implementation of the wrappers establishes a framework that supports an active approach to component-based software integration.

An Execution and Transaction Model for Active, Rule-Based Component Integration Middleware

The Integration Rules (IRules) project is investigating the use of active rules for supporting event-driven activity in applications involving distributed component integration. Integration rules respond to events that are raised during the execution of distributed transactions to evaluate conditions and trigger actions over distributed components that are implemented using the Enterprise Java Beans (EJB) component model. This paper presents the distributed architecture for the IRules environment and defines the execution and transaction model for the use of integration rules. The execution model includes traditional active rule coupling modes for immediate, deferred, and decoupled rule execution and also defines an asynchronous mode for concurrent rule and transaction execution. The flexible transaction model is used to allow integration rules, application transactions, and methods on EJB components to be executed as subtransactions within global distributed transactions. An execution scenario for the integration of EJB components is presented to illustrate the nested execution of rules and transactions for distributed component integration.

An active database approach to integrating black-box software components

Active database technology uses active rules, called Event-Condition-Action (ECA) rules, as an integral feature of application development. Active rules specify an event that the database monitors, a declarative condition to evaluate when the event occurs, and an action to execute when the condition is true. This paper motivates the use of active rules to develop a software application that is the result of integrating black-box software components. This approach focuses on integrating black-box JavaBeans/sup TM/ components, which generate Property Change Events when the values of its properties are modified. The changes in property values are known as deltas in the database community. DeltaBeans are introduced as a mechanism to monitor the changes or deltas to the properties of a black-box JavaBeans/sup TM/ component. This paper illustrates DeltaBeans in a simple application example and motivates the use of deltas to trigger active rules that specify application integration.

An evaluation of distributed computing options for a rule-based approach to black-box software component integration

This paper presents an evaluation of distributed object computing technology and the manner in which such tools can be used to construct a distributed framework for active rule processing. The results are presented in the context of the Integration Rules (IRules) project, which is investigating the middle-tier, rule processing technology necessary for the use of declarative, active rules in the integration of distributed, black-box components. Assuming the use of Enterprise Java Beans (EJBs) for component interfaces, we provide an evaluation of the event and transaction processing features of CORBA compared to the same capabilities using Jini Connection Technology. Through the simulation of integration rules, we identify the event and transaction processing issues that must be considered in the construction of distributed architectures for the interconnection of EJB components. The results of this investigation are being used to develop a general purpose, distributed rule processing architecture for integration rules within the IRules project.

The IRules Project

This paper provides an overview of the Integration Rules (IRules) approach to the interconnection of distributed software components. The intended use of this rule processing technology is for the specification of event-based processing logic in the development of component-based applications for distributed environments, such as E-commerce applications. The IRules approach builds upon the use of the Enterprise JavaBeans (EJB) software component model, providing an environment to facilitate the integration of black-box software components. An application integrator uses the IRules Component Definition Language to extend the definition of an EJB component in the IRules environment with derived and stored attributes, externalized relationships, and events. The application integrator then uses the IRules Integration Rule Language together with a scripting language to develop applications. Integration rules provide active rule capability to the environment so that as distributed components and external sources generate event notifications, integration rules are used to invoke methods on components or on higher-level application transactions. The IRules approach is unique in that it addresses the language and semantic framework needed in the context of software component models for the effective use of rules in distributed environments.