German Shegalov

XML-enabled workflow management for e-services across heterogeneous platforms

Abstract. Advanced e-services require efficient, flexible, and easy-to-use workflow technology that integrates well with mainstream Internet technologies such as XML and Web servers. This paper discusses an XML-enabled architecture for distributed workflow management that is implemented in the latest version of our Mentor-lite prototype system. The key asset of this architecture is an XML mediator that handles the exchange of business and flow control data between workflow and business-object servers on the one hand and client activities on the other via XML messages over http. Our implementation of the mediator has made use of Oracles XSQL servlet. The major benefit of the advocated architecture is that it provides seamless integration of client applications into e-service workflows with scalable efficiency and very little explicit coding, in contrast to an earlier, Java-based, version of our Mentor-lite prototype that required much more code and exhibited potential performance problems.

EOS: exactly-once E-service middleware

Publisher Summary This chapter aims to place failure handling logic into a generic Internet middleware framework so that failures are masked from application programs (and users). Application programs are, thus, relieved from handling message timeouts and other exceptions caused by system failures. Todays Web-based e-services do not handle system failures well. One of the most prominent examples is unintentional purchase of multiple copies of the same item in an online store. This may happen when the user sees a browser timeout for the final “checkout” (“place order”) request caused by a short outage or overload of the network or the backend servers (typically during peak load). Whereas the request may have been successfully, although slowly, processed, the user may attempt to send the checkout request once again, for example, by hitting the browser “refresh” button, unintentionally buying another copy of the same item. An e-service can be invoked either in a business-to-customer manner by a human user via the web browser or in a business-to-business manner by some other e-service.

A goal-driven auto-configuration tool for the distributed workflow management system mentorlite

The Mentor-lite prototype has been developed within the research project “Architecture, Configuration, and Administration of Large Workflow Management Systems” funded by the German Science Foundation (DFG). It has evolved from its predecessor Mentor [1], but aims at a simpler architecture. The main goal of Mentor-lite has been to build a light-weight, extensible, and tailorable workflow management system (WFMS) with small footprint and easy-to-use administration capabilities. Our approach is to provide only kernel functionality inside the workflow engine, and consider system components like history management and worklist management as extensions on top of the kernel. The key point to retain the light-weight nature is that these extensions are implemented as workflows themselves. The workflow specifications are interpreted at runtime, which is a crucial prerequisite for flexible exception handling and dynamic modifications during runtime. The interpreter performs a stepwise execution of the workflow specification according to its formal semantics. For each step, the activities to be performed by the step are determined and started. Mentor-lite supports a protocol for distributed execution of workflows spread across multiple workflow engines. This support is crucial for workflows that span large, decentralized enterprises with largely autonomous organizational units or even cross multiple enterprises to form so-called “virtual enterprises”. A communication manager is responsible for sending and receiving synchronization messages between the engines. In order to guarantee a consistent global state even in the presence of site or network failures, we have built reliable message queues using the CORBA Object Transaction Services. For administration, Mentor-lite provides a Java-based workbench for workflow design, workflow partitioning across multiple workflow servers, and a Java-based runtime monitoring tool.

Logging last resource optimization for distributed transactions in Oracle WebLogic server

State-of-the-art OLTP systems execute distributed transactions using XA-2PC protocol, a presumed-abort variant of the Two-Phase Commit (2PC) protocol. While the XA specification provides for the Read-Only and 1PC optimizations of 2PC, it does not deal with another important optimization, coined Nested 2PC. In this paper, we describe the Logging Last Resource (LLR) optimization in Oracle WebLogic Server (WLS). It adapts and improves the Nested 2PC optimization to/for the Java Enterprise Edition (JEE) environment. It allows reducing the number of forced (synchronous) writes and the number of exchanged messages when executing distributed transactions that span multiple transactional resources including a SQL database integrated as a JDBC datasource. This optimization has been validated in SPECjAppServer2004 (a standard industry benchmark for JEE) and a variety of internal benchmarks. LLR has been successfully deployed by high-profile customers in mission-critical high-performance applications.

Formal Verification of a Transactional Interaction Contract

A transactional information system guarantees as part of the ACID contract that multiple operations pertaining to a transaction are executed atomically and that if completed their effect is durable. However, message losses resulting from client and server crashes are not part of the transaction. Unlike failures occurring in the midst of a transaction (leading to its abort), the loss of a reply to the final commit message poses a problem of determining the transaction outcome that cannot be solved generically using state-of-the-art OLTP systems. This paper develops a formal specification of a generic transactional interaction contract that is part of a broader Interaction Contracts framework guaranteeing the exactly-once execution in general multi-tier applications. The formal specification is designed and verified using the statechart language and model checking in the reactive system design tool called Statemate.

Unstoppable stateful PHP web services

This paper presents the architecture and implementation of the EOS2 failure-masking framework for composite Web Services. EOS2 is based on the recently proposed notion of interaction contracts (IC), and provides exactly-once execution semantics for general, arbitrarily distributed Web Services in the presence of message losses and component crashes without requiring explicit coding effort by the application programmer. The EOS2 implementation masks failures by adding a recovery layer to popular Web technology products: (i) the server-side script language PHP run on Apache Web server, and (ii) Internet browsers like IE to deliver recovery guarantees to the end-user.