This article discusses the challenges in computer systems research posed by the emerging field of pervasive computing. It first examines the relationship of this new field to its predecessors: distributed systems and mobile computing. It then identifies four new research thrusts: effective use of smart spaces, invisibility, localized scalability, and masking uneven conditioning. Next, it sketches a couple of hypothetical pervasive computing scenarios, and uses them to identify key capabilities missing from today's systems. The article closes with a discussion of the research necessary to develop these capabilities.

/pdf/pervasive-computing-vision-and-challenges-8dv8bu4mg9.pdf

Pervasive computing: vision and challenges

This third edition of a classic textbook can be used to teach at the senior undergraduate and graduate levels. The material concentrates on fundamental theories as well as techniques and algorithms. The advent of the Internet and the World Wide Web, and, more recently, the emergence of cloud computing and streaming data applications, has forced a renewal of interest in distributed and parallel data management, while, at the same time, requiring a rethinking of some of the traditional techniques. This book covers the breadth and depth of this re-emerging field. The coverage consists of two parts. The first part discusses the fundamental principles of distributed data management and includes distribution design, data integration, distributed query processing and optimization, distributed transaction management, and replication. The second part focuses on more advanced topics and includes discussion of parallel database systems, distributed object management, peer-to-peer data management, web data management, data stream systems, and cloud computing. New in this Edition: New chapters, covering database replication, database integration, multidatabase query processing, peer-to-peer data management, and web data management. Coverage of emerging topics such as data streams and cloud computing Extensive revisions and updates based on years of class testing and feedback Ancillary teaching materials are available.

Principles of Distributed Database Systems

Mining for a.ssociation rules between items in a large database of sales transactions has been described as an important database mining problem. In this paper we present an efficient algorithm for mining association rules that is fundamentally different from known algorithms. Compared to previous algorithms, our algorithm not only reduces the I/O overhead significantly but also has lower CPU overhead for most cases. We have performed extensive experiments and compared the performance of our algorithm with one of the best existing algorithms. It was found that for large databases, the CPU overhead was reduced by as much as a factor of four and I/O was reduced by almost an order of magnitude. Hence this algorithm is especially suitable for very large size databases.

/pdf/an-efficient-algorithm-for-mining-association-rules-in-large-13vj5oh7om.pdf

An Efficient Algorithm for Mining Association Rules in Large Databases

This survey covers rollback-recovery techniques that do not require special language constructs. In the first part of the survey we classify rollback-recovery protocols into checkpoint-based and log-based.Checkpoint-based protocols rely solely on checkpointing for system state restoration. Checkpointing can be coordinated, uncoordinated, or communication-induced. Log-based protocols combine checkpointing with logging of nondeterministic events, encoded in tuples called determinants. Depending on how determinants are logged, log-based protocols can be pessimistic, optimistic, or causal. Throughout the survey, we highlight the research issues that are at the core of rollback-recovery and present the solutions that currently address them. We also compare the performance of different rollback-recovery protocols with respect to a series of desirable properties and discuss the issues that arise in the practical implementations of these protocols.

/pdf/a-survey-of-rollback-recovery-protocols-in-message-passing-bnrpate93a.pdf

A survey of rollback-recovery protocols in message-passing systems

Database management systems will continue to manage large data volumes. Thus, efficient algorithms for accessing and manipulating large sets and sequences will be required to provide acceptable performance. The advent of object-oriented and extensible database systems will not solve this problem. On the contrary, modern data models exacerbate the problem: In order to manipulate large sets of complex objects as efficiently as today's database systems manipulate simple records, query-processing algorithms and software will become more complex, and a solid understanding of algorithm and architectural issues is essential for the designer of database management software. This survey provides a foundation for the design and implementation of query execution facilities in new database management systems. It describes a wide array of practical query evaluation techniques for both relational and postrelational database systems, including iterative execution of complex query evaluation plans, the duality of sort- and hash-based set-matching algorithms, types of parallel query execution and their implementation, and special operators for emerging database application domains.

/pdf/query-evaluation-techniques-for-large-databases-45td1anbls.pdf

Query evaluation techniques for large databases

Workflow management has become a fairly hot topic during the past two or three years. There is an increasing number of new products, and in addition, numerous vendors that have been around for a while have discovered that what their products actually do is workflow management. Terminology is just as undefined as in any other field of our discipline, and so it is not trivial to define precisely what workflow actually is, which components it includes, how the minimal functionality can be characterized, and so on. A consortium of vendors, users and researchers called . “workflow coalition” has been established to sort out these issues, to find a a reference model, and come up with standards wherever this seems possible. Although this group has making good progress, it has not had much influence on existing products yet. The kinds of services which are currently subsumed under the heading of “workflow management?’ come from very different origins. Some of them are functionally enhanced mail systems; the most notable example of this group is Lotus Notes. Another group is defined by TPmanagers, which typically also have some kind of highlevel controlflow language, such as STDL. A third group comprises those systems, which have been developed as workflow .management systems “from first principles”, generalizing the ideas one cannot find in production planning systems, job control systems, etc. A typical example of this approach is IBM’s BlowMark system. Now, is there anything database-specific in workflow management? Consider that the key purpose of workflow management is to orchestrate, control, supervise and schedule the execution and dependencies of a large number of related activities, the completion of which may take a fairly long time. Qpically, some of the activities of a complex workflow script will execute transactions against some shared database, but this is not the topic of this panel. The key aspect is the long duration of the computation defined by a worktlow specification. Since such computations can go on for days, weeks, or months, they will accumulate a large amount of “state”, which is not shared with anybody else, but as private that particular worktlow execution. But because it is a long-lived computation, it must be guaranteed that no hardware or software failure can stop it or cause it to roll back, it rather has to be rolled forward according io the specification, which means appropriate recovery mechanisms and preservation of the state information in the presence of failures. Maintaining state is something database-systems are good at.; On the other hand, under the transaction paradigm they do roll back recovery in case of a failure rather than rolling things forward to the most recent state. But the obvious question is, where the database systems should be functionally enhanced in order.to support worktlow management systems, or whether those systems should roll their own. The second interesting issue has to do with synchronization of accesses by workflow activities on shared databases. We assume that the database accesses issued by activities being part of the workflow are covered by conventional transactions. This means all locks are released at the end of the transaction, but of course the workflow still goes on, and most likely there are consistency constraints expressed in terms ef data intershare, database which are relevant for the workflow in the long run. So the question is how to maintain “long-lived” consistency constraints on ‘shared data for individual workflowswithout making conventional-locks long-livedbecause this would be an obviously bad idea. This looks like a database problem, or at least it has a lot to do with databases. The third group of problems has to do withevent& Events play an important role incoordinating and synchronizing the activities within a workflow, and due to the recoverability requirements, events have to be recoverable, too. The, question here is, what databases can do in support of “stable” events, and whether this is,similar to what is discussed in’ the field of active databases. To sum it up: Even though the functional requirements for workilow management systems are just beginning to emerge, I think there is clear evidence for. the need of additional database functionality in order to support such systems. ,f

/pdf/databases-and-workflow-management-what-is-it-all-about-panel-t5dc8mgybb.pdf

Andreas Reuter

Papers

Databases and Workflow Management: What is it All About? (Panel)