In recent years, numerous transaction models have been proposed to address the problems posed by advanced database applications, but only a few of these models are being used in commercial products. In this paper, we make the case that such models may be too centered around databases to be useful in real environments. Advanced applications raise a variety of issues that are not addressed at all by transaction models. These same issues, however, are the basis for existing workflow systems, which are having considerable success as commercial products in spite of not having a solid theoretical foundation. We explore some of these issues and show that, in many aspects, workflow models are a superset of transaction models and have the added advantage of incorporating a variety of ideas that to this date have remained outside the scope of traditional transaction processing. 1 Introduction It is a widely accepted fact that conventional databases are unsuitable for many applications. To addr...

This paper presents the distributed architecture of the WIDE workflow management system. We show how distribution and scalability are obtained by the use of a distributed object model, a client /server architecture, and a distributed workflow server architecture. Specific attention is paid to the extended transaction support and active rule support subarchitectures. 1. Introduction to WIDE Workflow management is currently considered a major application domain for information technology. To provide reliable data processing in workflow applications, database systems have become important as the basis for workflow management systems. In the WIDE project, extended database technology is developed to serve as the basis for a commercial next-generation workflow management system. In WIDE, extending database technology focuses on extended transaction management and active rule support. Extended transaction management provides flexible and reliable workflow process semantics, active rule sup...

The construction of software systems from pre#existing# independently developed software components will only occur when application builders can adapt software components to suit their needs. We propose that soft# ware components provide two interfaces # one for be# havior and one for adapting that behavior as needed. The ADAPT framework presented in this paper sup# ports both component designers in creating components that can easily be adapted# and application builders in adapting software components. The motivating exam# ple# using JavaBeans# shows how adaptation# not cus# tomization# is the key to component#based software. KEYWORDS Software components# JavaBeans# Adaptation 1 INTRODUCTION An important aim of software engineering is to produce reliable and robust software systems. As software sys# tems grow in size# however# it becomes infeasible to de# sign and construct software systems from scratch. Most software developers are familiar with reusing code from component libra...

In this paper we describe our experience applying the concepts of reflection to a legacy transaction processing (TP) monitor in order to support the implementation of extended transaction models. In the past ten years, numerous extended transaction models have been proposed to address the challenges posed by new advanced applications. Few practical implementations of these extended transaction models exist and none are being used in a commercial TP monitor. We believe the reason for this state of affairs is that the interface and functionality of commercial TP monitors is "locked in" to a fixed transaction model. We have developed the Reflective Transaction Framework as a practical method to implement extended transaction models on a commercial TP monitor. The design of our framework is based on the principles of computational reflection, and in particular open implementation.

Database management systems #DBMSs# have been increasingly used for advanced application domains# such as software development environments# network management# workflow management systems# computer-aided design and manufacturing# and managed healthcare. In these domains# the standard correctness model of serializability is often too restrictive. We introduce the notion of a Concurrency Control Language #CCL# that allows a database application designer to specify concurrency control policies to tailor the behavior of a transaction manager. A well-crafted set of policies defines an extended transaction model. The necessary semantic information required by the CCL run-time engine is extracted from a task manager# a #logical# module by de#nition included in all advanced applications. This module stores task models that encode the semantic information about the transactions submitted to the DBMS. We have designed a rule-based CCL# called cord# and have implemented a run-time engine that ca...

rnal Concurrency Control (ECC) architecture that captures the essence of advanced database applications. We show how a transaction manager can employ semantic information from the Task Management Layer (TML) of these applications. Our mediator-based architecture allows for flexible integration of a transaction manager component with advanced database applications and provides for generic extraction of semantic information from database applications. The Pern transaction manager component we implemented realizes the ECC architecture. Pern employs a declarative concurrency control language, called Cord that determines how to extend the behavior of transactions. Using Cord, an ETM is specified by its extensions to serializability. Pern can then support the desired ETM by applying Cord rules during transaction execution. Cord is practical since it assumes that the transaction

Research in software architecture has emphasized compositional development, where the computational aspects of a system are modularly separated from communication and coordination aspects. Typically, software architectures are factored into a set of components, which encapsulate computation, and connectors, which encapsulate interactions. In terms of design, development and debugging, this separation has several important advantages. In particular, by separating application code from the protocols used for interaction, software components may be independently developed and tested. Moreover, as requirements change, existing architectural elements may be modularly replaced by new elements with appropriate properties. A fundamental problem with these abstractions is their interaction with "cross-cutting" architectural features such as heterogeneity, availability, and adaptability. Availability, for example, requires protocols that manipulate both communication and resources. Controlling architectural resources, however, requires access to the internal resource usage patterns of components and connectors. Unfortunately, current architectural abstractions have inflexible interfaces which obscure these patterns. This loss of information forces the implementation of such features to be hard-coded within architectural elements, eliminating many advantages of the modular approach. In this thesis, we propose a model for distributed software architectures that exposes resource access in a modular fashion. Our model extends current architectural abstractions by providing a meta-architecture for customization. This meta-architecture augments the functional interface of architectural elements with an operational interface for controlling resources. We also develop a formal semantic...

Workflow management systems (WFMS) support the modeling and coordinated execution of processes within an organization. To coordinate the execution of the various activities (or tasks) in a workflow, task dependencies are specified among them. As advances in workflow management take place, they are also required to support security. In a multilevel secure (MLS) workflow, tasks may belong to di#erent security levels. Ensuring the dependencies from the tasks at higher security levels to those at lower security levels (high-to-low dependencies) may compromise security. In this paper, we consider such MLS workflows and show how they can be executed in a secure and correct manner. Our approach is based on semantic classification of the task dependencies that examines the source of the task dependencies. We classify the high-to-low dependencies in several ways: conflicting versus conflict-free, result-independent versus result-dependent, strong versus weak, and abortive versus non-abortive. W...

We describe a method for building a variety of coor-dination protocols as well as distributed extended trans-action primitives. The method is called Open Coordi-nation Protocol (OCP), and we apply OCP to construct many variants of Commit_Transaction [15, 13, 22, 12], as well as distributed Split_Transaction [18] and distributed Join_Group [14, 20]. OCP adopts a modular decomposi-tion of popular coordination protocols (e.g., two-phase com-mit) into microprotocols [17], and then chooses appropri-ate microprotocols to build new coordination protocols or extended transaction primitives with desired features (e.g., Split_transaction with read-only optimization). We use in-cremental specialization [6, 19] to improve the e~ciency of each implemented protocol. 1

We report on the issues raised when designing a customizable locking mechanism for Persistent Java, a type-safe, object-oriented, orthogonally persistent system based on the language Java. Customizable locking mechanisms are supported by locking capabilities. A locking capability is a book-keeper of locks that automatically acquires locks with a customizable conflict detection mechanism. It implements the concepts of delegation of locks and ignorable conflicts, automatically keeps track of the dependencies created because of allowance of conflicts, supports querying of details about these dependencies, and supports the setting of user-defined notifications for conflicts that can't be ignored. Locking capabilities don't change the Java language specification, and allow use of any Java classes without changing a single line of their code to implement the body of transactions. We also present several novel techniques to implement efficiently this customizable locking mechanism in a persis...