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As pointed out in Section 6.2, there is a high demand of workflow management systems in large organizations. However, existing solutions are still limited. Most of these efforts have concentrated on conceptual transaction models, concurrent versions of algorithms, or theoretical results on model correctness. Relatively little attention has been given to the software development environments that are required to convert these efforts into operational distributed application programs. This chapter presents the Transaction-Oriented Workflow Environment (TOWE) system for programming workflow activities.

For databases to be interoperable, they need to bridge the dissimilarities that exist between their systems. However, in most cases, no a-priori contingency plans are put in place to deal with eventual interoperation. In that respect, there is a need to re-engineer the participating databases to achieve a seamless cooperation. This includes addressing the different aspects of database heterogeneity. Essentially, database heterogeneity can be of many forms (Sheth and Larson, 1990) (Bouguettaya et al., 1995b) (Batini et al., 1986) (Hammer and McLeod, 1993).

Advances in wide area networking are making the goal of achieving a worldwide interoperable database system closer than ever. In a large network of interoperable autonomous heterogeneous databases, the architecture should be flexible enough to allow negotiation to take place to establish grouping of databases. In such an environment, it is important that databases be made aware of other participating databases in an incremental fashion. Furthermore, users should be educated about the space of information in an incremental and dynamic fashion. These goals are to be achieved under the major assumptions that participating databases keep their autonomy intact as much as possible and that the overhead in bridging heterogeneity be proportional to the level of sharing. In this chapter, we present a system for describing, locating, and accessing data in large networks of databases. The use of flexible constructs such as service links, coalitions, and co-databases facilitates data organization, discovery, and sharing. A language supporting the definition and manipulation of these constructs is also proposed. We propose an implementation using CORBA (Common Object Request Broker) and Web technologies to support scalable and portable architecture interconnecting large networks of heterogeneous and autonomous databases.

It has been over ten years since the first workflow product was introduced. Despite the large number of workflow vendors and various research efforts all over the world, as well as the hype about the workflow market, workflow technology is still far from pervasive. This paper assesses the situation from a technical point of view, focusing on the development and enactment aspects of workflow processes. We discuss the current capabilities of workflow products, major issues that need to be addressed before workflow can be pervasive, as well as possible future trends and research that will help workflow succeed.

Replication introduces a tension between query optimization and remote access control in a distributed database system. If we view a transaction as a partially-ordered set of queries and updates, then factors that affect quorum selection for the fragments accessed by a transaction as a whole are currently orthogonal to factors that affect the replica selection during the planning of individual queries. Therefore, the two processes may act at cross-purposes to one another. Query optimization considers an individual query and selects a set of fragments that minimizes the computation and communication cost and allows computation to be pushed into the local site. Transaction management, on the other hand, selects quorums (sets of replicas to retrieve) based on replica availability and on mutual consistency constraints such as quorum intersection among write operations or between read and write operations. Thus, transaction optimization narrows the “optimal” solution space for the queries it contains Hence, transaction management should cooperate with query optimization to optimize transaction processing.

In a mobile computing environment, a user carrying a portable computer can execute a mobile t11m,,· action by submitting the ope.rations of the transaction to distributed data servers from different locations. M a result of this mobility, the operations of the transaction may be executed at different servers. The distribution oC operations implies that the transmission of messages (such as those involved in a two phase commit protocol) may be required among these data servers in order to coordinate the execution ofthese operations. In this paper, we will address the distribution oC operations that update partitioned data in mobile environments. We show that, for operations pertaining to resource allocation, the message overhead (e.g., for a 2PC protocol) introduced by the distribution of operations is undesirable and unnecessary. We introduce a new algorithm, the RenlnJation Algorithm (RA), that does not necessitate the incurring of message overheads Cor the commitment of mobile transactions. We address two issues related to the RA algorithm: a termination protocol and a protocol for non_partition.commutotive operation". We perform a comparison between the proposed RA algorithm and existing solutions that use a 2PC protocol.

We present a new lock management scheme which allows a read unlock for an item to be executed at any copy site of that item; the site may be different from the copy site on which the read lock is set. The scheme utilizes the replicated copies of data items to reduce the message costs incurred by the mobility of the transaction host. We demonstrate this idea in an optimistic locking algorithm called O2PL-MT (Optimistic Two Phase Locking for Mobile Transactions). Like its counterpart algorithm O2PL (Optimistic Two Phase Locking), O2PL-MT grants read locks immediately on demand and defers write locks until the commitment time. However, O2PL-MT requires the transmission of fewer messages than O2PL in a mobile environment in which data items are replicated.

We describe a Biomedical INteroperable Database System (BIND), which is part of a larger research project, the Biomedical Equipment Assessment and Management (BEAM) system. BEAM is an AIM (Advanced Informatics in Medicine) awarded project and it is funded by the European Community. It integrates a number of heterogeneous database systems which store Biomedical information, over public communications networks. The databases are located in various European countries. Users access the information via a common user interface and are able to run transactions over the multidatabase system.

This paper presents the InterSQL transaction programming language used in the InterBase-Star multidatabase system. InterBase-Star supports the atomic execution of transactions over heterogeneous, autonomous, and distributed component database systems. The component systems may use a variety of commitment methods, including ones recently developed specifically for multidatabase systems. Some of these new methods require the specification of semantic actions (e.g. compensating actions that semantically undo the effects of a subtransaction), and it is possible that multiple commitment methods may be used. Therefore, one requires the ability to specify which commitment methods may be used, and, for certain methods, semantic actions that are used to effect commitment. InterSQL is an object-oriented SQL-based transaction programming language that supports the specification of multidatabase transactions whose subtransactions may use various and multiple commitment methods.

Develops a formal basis for research into the reliability aspects of transaction processing in multidatabase systems (MDBSs). We define a new correctness notion called 'global committability' for the correct unilateral commit and the retry recovery of global transactions in an autonomous MDBS environment. This notion makes it easier to ensure the isolation property of global transactions when the retry approach is applied. The formalization work illustrates that the conventional serializability and recoverability notions are not sufficient to specify the correct execution (i.e. isolated execution and recovery) of global transactions when the unilateral commit and the retry recovery are used to ensure the atomicity of global transactions. This work is significant because the unilateral commit and the retry recovery are an attractive complementary means to the undo recovery (whose correct schedule is specified by the conventional recoverability notion) for advanced transaction applications with the characteristics of site autonomy and long-lived execution.

This article presents a theoretical basis for global concurrency control to maintain global serializability in multidatabase systems. Three correctness criteria are formulated that utilize the intrinsic characteristics of global transactions to determine the serialization order of global subtransactions at each local site. In particular, two new types of serializability, chain-conflicting serializability and sharing serializability, are proposed and hybrid serializability, which combines these two basic criteria, is discussed. These criteria offer the advantage of imposing no restrictions on local sites other than local serializability while retaining global serializability. The graph testing techniques of the three criteria are provided as guidance for global transaction scheduling. In addition, an optimal property of global transactions for determinating the serialization order of global subtransactions at local sites is formulated. This property defines the upper limit on global serializability in multidatabase systems.

A theoretical basis for global transaction scheduling to maintain global serializability in multidatabase systems is presented. Three correctness criteria are formulated to utilize the intrinsic characteristics of global transactions at the global level to determine the serialization order of global subtransactions at each local site. In particular, two new types of serializability, chain-conflicting serializability and sharing serializability, are proposed, and an optimal criterion (termed hybrid serializability) combining these two basic criteria is discussed. These criteria offer the advantage of imposing no restrictions on local sites while retaining global serializability. In addition, the optimal aspect of hybrid serializability defines limits on global serializability in multidatabase systems. >

The realization of truly heterogeneous database systems is hampered by two principal obstacles. One is the unsuitability of traditional transaction models; this has led to the proposal of a number of new, advanced transaction models. The second is the lack of appropriate programming support for these advanced concepts. This paper addresses these two issues by pointing out the advantages of using a logic-based approach for the integration of autonomous software systems.

For many applications, a multidatabase approach constitutes an attractive alternative to a single, integrated database. In this paper we describe our experiences gained in the course of the development of experimental multidatabase systems: OMNIBASE, at the University of Houston and InterBase at Purdue University. We concentrate on the problems of query processing and multidatabase transaction management and discuss solutions that were developed within both projects. We identify the main issues related to supporting updates spanning across multiple autonomous databases and define an extended transaction model suitable for heterogeneous computing environments. Then we review the major outstanding research problems and discuss the directions of further research in the area of multidatabase systems.

In this article, several practical algorithms are proposed to support content-based video analysis, modeling, representation, summarization, indexing, and access. First, a multilevel video data- base model is given. One advantage of this model is that it provides a reasonable approach to bridging the gap between low-level rep- resentative features and high-level semantic concepts from a hu- man point of view. Second, several model-based video analysis techniques are proposed. In order to detect the video shots, we present a novel technique, which can adapt the threshold for scene cut detection to the activities of variant videos or even different video shots. A seeded region aggregation and temporal tracking technique is proposed for generating the semantic video objects. The semantic video scenes can then be generated from these extracted video access units (e.g., shots and objects) according to some domain knowledge. Third, in order to categorize video contents into a set of semantic clusters, an integrated video classification technique is de- veloped to support more efficient multilevel video representation, summarization, indexing, and access techniques. © 2001 SPIE and

In this paper, a centralized deadlock detection algorithm with multiple outstanding requests (CDDMOR) is proposed for use in distributed database systems and transaction-processing systems. This algorithm allows a process to request many resources simultaneously. While a centralized scheme is superior to a completely distributed scheme in terms of performance, a major problem of such a scheme is congestion. Therefore, an important extension to the basic CDDMOR, a partially distributed scheme, is proposed to alleviate the problem of congestion, as well as to take advantage of the result presented by several researchers that global (multisite) deadlocks are infrequent. It takes care of the local (single site) deadlocks without involving other sites and uses centralized deadlock detection only when there is a possibility of global deadlock.

Synthesis of multiple randomized controlled trials (RCTs) in a systematic review can summarize the effects of individual outcomes and provide numerical answers about the effectiveness of interventions. Filtering of searches is time consuming, and no single method fulfills the principal requirements of speed with accuracy. Automation of systematic reviews is driven by a necessity to expedite the availability of current best evidence for policy and clinical decision-making. We developed Rayyan ( http://rayyan.qcri.org ), a free web and mobile app, that helps expedite the initial screening of abstracts and titles using a process of semi-automation while incorporating a high level of usability. For the beta testing phase, we used two published Cochrane reviews in which included studies had been selected manually. Their searches, with 1030 records and 273 records, were uploaded to Rayyan. Different features of Rayyan were tested using these two reviews. We also conducted a survey of Rayyan’s users and collected feedback through a built-in feature. Pilot testing of Rayyan focused on usability, accuracy against manual methods, and the added value of the prediction feature. The “taster” review (273 records) allowed a quick overview of Rayyan for early comments on usability. The second review (1030 records) required several iterations to identify the previously identified 11 trials. The “suggestions” and “hints,” based on the “prediction model,” appeared as testing progressed beyond five included studies. Post rollout user experiences and a reflexive response by the developers enabled real-time modifications and improvements. The survey respondents reported 40% average time savings when using Rayyan compared to others tools, with 34% of the respondents reporting more than 50% time savings. In addition, around 75% of the respondents mentioned that screening and labeling studies as well as collaborating on reviews to be the two most important features of Rayyan. As of November 2016, Rayyan users exceed 2000 from over 60 countries conducting hundreds of reviews totaling more than 1.6M citations. Feedback from users, obtained mostly through the app web site and a recent survey, has highlighted the ease in exploration of searches, the time saved, and simplicity in sharing and comparing include-exclude decisions. The strongest features of the app, identified and reported in user feedback, were its ability to help in screening and collaboration as well as the time savings it affords to users. Rayyan is responsive and intuitive in use with significant potential to lighten the load of reviewers.