The basic transaction model has evolved over time to incorporate more complex transaction structures and to selectively modify the atomicity and isolation properties. In this chapter we discuss the application of transaction concepts to activities that involve coordinated execution of multiple tasks (possibly of different types) over different processing entities. Such applications are referred to as transactional workflows. In this chapter we discuss the specification of such workflows and the issues involved in their execution. 1 What is a Workflow? Workflows are activities involving the coordinated execution of multiple tasks performed by different processing entities. A task defines some work to be done and can be specified in a number of ways, including a textual description in a file or an email, a form, a message, or a computer program. A processing entity that performs the tasks may be a person or a software system (e.g., a mailer, an application program, a database mana...

The main difficulty in enforcing global serializability in a multidatabase environment lies in resolving indirect (transitive) conflicts between multidatabase transactions. Indirect conflicts introduced by local transactions are difficult to resolve because the the behavior or even the existence of local transactions is not known to the multidatabase system. To overcome these problems, we propose to incorporate additional data manipulationoperations in the subtransactions of each multidatabase transaction. We show that if these operations create direct conflicts between subtransactions at each participating local database system, indirect conflicts can be resolved even if the multidatabase system is not aware of their existence. Based on this approach we introduce a multidatabase transaction management method that requires the local database systems to ensure only local serializability. The proposed method and its refinements do not violate the autonomy of the local database systems an...

Service order provisioning is an important telecommunication application that automates the process of providing telephone services in response to the customer requests. It is an example of a multi-system application that requires access to multiple, independently developed application systems and their databases. In this paper, we describe the design and implementation of a prototype system 1 that supports the execution of the Flexible Transactions and its use to develop the service order provisioning application. We argue that such approach may be used to support the development of multi-system, flow-through processing applications in a systematic and organized manner. Its advantages include fast and easy specification of new services, support for testing of the declaratively specified work-flows, and the specification of potential concurrency among the tasks constituting an application.

To enforce global serializability in a multidatabase environment themultidatabase transaction manager must take into account the indirect (transitive) conflicts between multidatabase transactions caused by local transactions. Such conflicts are difficult to resolve because the behavior or even the existence of local transactions is not known to the multidatabase system. To overcome these difficulties, we propose to incorporate additional data manipulation operations in the subtransactions of each multidatabase transaction. We show that if these operations create direct conflicts between subtransactions at each participating local database system, indirect conflicts can be resolved even if the multidatabase system is not aware of their existence. Based on this approach, we introduce optimistic and conservative multidatabase transaction management methods that require the local database systems to assure only local serializability. The proposed methods do not violate the autonomy of the local database systems and guarantee global serializability by preventing multidatabase transactions from being serialized in different ways at the participating database systems. Refinements of these methods are also proposed for multidatabase environments where the participating database systems allow schedules that are cascadeless or transactions have analogous execution and serialization orders. In particular, we show that forced local conflicts can be eliminated in rigorous local systems, local cascadelessness simplifies the design of a global scheduler and that local strictness offers no significant advantages over cascadelessness.

Workflow management systems (WFMSs) more and more become the basic technology for organizations to perform their daily business processes (workflows). A consistent and reliable execution of such processes is crucial for all organizations. We claim that this can only be achieved by integrating transactional features - especially "workflow transactions " - into WFMSs. Based on this idea, we discuss in detail advanced workflow recovery concepts which are necessary for the reliable and consistent execution of business processes in the presence of failures and exceptions. Additionally, we distinguish between different workflow types and present adequate recovery concepts for each of them. 1.

A method for integrated concurrency control and recovery, applicable to heterogeneous multidatabase systems is proposed 1 . The role of the participant in the two-phase commit protocol is laid on an entity called 2PC Agent associated with the local database system. The main importance of the method is in preserving global serializability in the presence of unilateral aborts and site failures. The method requires the participating database systems to use the strict two-phase locking or a comparable rigorous concurrency control policy. Introduction There has recently been much interest in integrating pre-existing databases managed by heterogeneous database management systems (DBMS). This is understood to be caused by the need to eliminate "islands of information" [11] and, generally, the necessity to improve the interoperability of database systems [23]. There are various architectures supporting these objectives. The multidatabase architecture [25] is characterized by preserving vari...

Whereas serializability captures database consistency requirements and transaction correctness properties via a single notion, recent research has attempted to come up with correctness criteria that view these two types of requirements independently. The search for more flexible correctness criteria is partly motivated by the introduction of new transaction models that extend the traditional atomic transaction model. These extensions came about because the atomic transaction model in conjunction with serializability is found to be very constraining when used in advanced applications, such as design databases, that function in distributed, cooperative, and heterogeneous environments. In this paper, we develop a taxonomy of various correctness criteria that focus on database consistency requirements and transaction correctness properties from the viewpoint of what the different dimensions of these two are. This taxonomy allows us to categorize correctness criteria that have been proposed...

Whereas serializability captures database consistency requirements and transaction correctness properties via a single notion, recent research has attempted to come up with correctness criteria that view these two types of requirements independently. In this paper, we develop a taxonomy of various correctness criteria that focus on database consistency requirements and transaction correctness properties from the viewpoint of what the different dimensions of these two are. This taxonomy allows us to categorize correctness criteria that have been proposed in the literature. To help in this categorization, we have applied a uniform specification technique, based on ACTA, to express the various criteria. Such a categorization helps shed light on the similarities and differences between different criteria and to place them in perspective. To appear in Distributed Object Management, Ozsu, Dayal, and Valduriez Ed., Morgan Kaufmann Publishers, 1993 1 INTRODUCTION database co...

InaresearchandtechnologyapplicationprojectatBell- core,weusedmultidatabasetransactionstomodelmulti- systemworkflowsoftelecommunicationapplications.Dur- ingtheprojectaprototypeschedulerforexecutingmulti- databasetransactionswasdeveloped. Twooftheissues addressedinthisprojectwereconcurrentexecutionofmulti- databasetransactionsandtheirfailurerecovery.Thispaper discussesouruseofpropertiesoftheapplicationandthe telecommunicationsystemstodevelopsimpleandefficient solutionstotheconcurrencycontrolandrecoveryproblems. 1

Workflow management systems are finding wide applicability in small and large organizational settings. In this paper, we briefly review four large-scale applications to gauge their modeling and run-time requirements. Advanced transaction models (ATM) focus on maintaining data consistency and have provided solutions to many problems such as correctness, consistency, and reliability in transaction processing and database management environments. While such concepts have yet to be solved in the domain of workflow systems, database researchers have proposed to use, or attempted to use ATMs to model workflows. In this paper, we argue that workflow requirements in large-scale enterprise-wide applications involving heterogeneous and distributed environments far exceed the modeling and functionality support provided by ATMs, and suggest that an ATM is unlikely to provide a primary basis for workflow modeling and subsequent management. We have also presented various connotations of the term transaction that exist in the real-world organizational processes. Finally, we point out the need for looking beyond ATMs and using a multi-disciplinary approach for modeling large-scale workflow applications of the future.