Research On Transactional Workflows In Network Distributed Environment

Transaction technology is a key technology to ensure consistence and reliability in information systems. The most frequently used flat transactions are atomic operation sequences with ACID (atomicity, consistency, isolation and durability) characteristics. However, the flat transactions cannot provide sufficient supports for applications with complex business processes.The general workflow model, on the other hand, supports rich business process logic for coordination of independent activities, but with little transactional aspect. The transactional workflow model can be regarded as the merging point of transaction processing technology and general workflow model; it is motivated to support both transactional aspect and business process aspect of an application. Transactional workflow technology is promising for future distributed applications.In this thesis, we studied several key issues of transactional workflows. First, we developed a formal model, namely ISTWM, for transactional workflows. ISTWM specifies both structural and executive aspects of transactional workflows. We formally defined the concept of well-formedness as a structural correctness criteria for transactional workflows. An effective method for well-formedness validation was also proposed. ISTWM considers the correctness of concurrent execution as well, and specifies the definition of serializible and recoverable schedules.Second, we proposed a new scheduling protocol for transaction workflows. Due to different termination characteristics of transactions, only one workflow is allowed to execute non-compensatable transactions with current scheduling protocols. In our approach, we defined two granularities of conflict based on transaction classes and on transaction instances, and we developed a scheduling protocol using both granularities of conflict detection. Our method provides a higher degree of concurrency in following two ways: fine-grained locking mechanism based on transaction instances is used to reduce the conflict possibility among concurrent workflows; on the other hand, the coarse-grained conflict mechanism based on transaction classes is used to predict future conflict among workflows, multiple workflows are therefore allowed to execute non-compensatable transactions if they do not conflict in future.Third, we designed a transactional workflow description language ISTWL in context-free grammar. The data flow is implemented by context variables in ISTWL. ISTWL supports a rich set of control structures, including sequential, parallel, contingency, conditional and iterative structures. Enhanced with these features, ISTWL can be used to specify complex business process. Novel features of ISTWL include the specification of termination characteristics and conflict detection.Fourth, we designed and implemented a comprehensive environment supporting transactional workflows. The key components of the environment are message queueing system ISMQ and distributed transaction processing monitor ISTX. We used design patterns and object-oriented framework technology extensively in these systems. An object-oriented framework ISTM for multilevel transaction recovery was proposed to provide reusable transaction recovery mechanism. ISTM has been successfully employed in the implementation of ISMQ. A C++ wrapper for multiple network programming interfaces UniChannels was designed in ISMQ, which is used to handle with heterogeneity of distributed network environment. ISTX supports distributed transaction management, recovery and connection pooling. Moreover, ISMQ and ISTX provide standard interfaces IMS and JTA, respectively.Lastly, a prototype system ISTW for transactional workflows is implemented in J2EE environment. ISTW uses the JMS service provided by ISMQ and the JTA/JTS services provided by ISTX. Transactions in ISTW are implemented by session beans, and the interaction among transactions is realized via message queues. For simplicity, a centralized scheduler is used in ISTW, and an activity manager is running at each node in ISTW.