Concurrency Control in Advanced Database Applications

Concurrency control has been thoroughly studied in the context of traditional database applications such as banking and airline reservations systems. There are relatively few studies, however, that address the concurrency control issues of advanced database applications such as CAD/CAM and software development environments. The concurrency control requirements in such applications are different from those in conventional database applications; in particular, there is a need to support non-serializable cooperation among users whose transactions are long-lived and interactive, and to integrate concurrency control mechanisms with version and configuration control. This paper outlines the characteristics of data and operations in some advanced database applications, discusses their concurrency control requirements, and surveys the mechanisms proposed to address these requirements

Concurrency Control in Advanced Database Applications

Concurrency control has been thoroughly studied in the context of traditional database applications such as banking and airline reservations systems. There are relatively few studies, however, that address the concurrency control issues of advanced database applications such as CAD/CAM and software development environments. The concurrency control requirements in such applications are different from those in conventional database applications; in particular, there is a need to support non-serializable cooperation among users whose transactions are long-lived and interactive, and to integrate concurrency control mechanisms with version and configuration control. This paper outlines the characteristics of data and operations in some advanced database applications, discusses their concurrency control requirements, and surveys the mechanisms proposed to address these requirements

Proceedings of the ECSCW'95 Workshop on the Role of Version Control in CSCW Applications

The workshop entitled "The Role of Version Control in Computer Supported Cooperative Work Applications" was held on September 10, 1995 in Stockholm, Sweden in conjunction with the ECSCW'95 conference. Version control, the ability to manage relationships between successive instances of artifacts, organize those instances into meaningful structures, and support navigation and other operations on those structures, is an important problem in CSCW applications. It has long been recognized as a critical issue for inherently cooperative tasks such as software engineering, technical documentation, and authoring. The primary challenge for versioning in these areas is to support opportunistic, open-ended design processes requiring the preservation of historical perspectives in the design process, the reuse of previous designs, and the exploitation of alternative designs. The primary goal of this workshop was to bring together a diverse group of individuals interested in examining the role of versioning in Computer Supported Cooperative Work. Participation was encouraged from members of the research community currently investigating the versioning process in CSCW as well as application designers and developers who are familiar with the real-world requirements for versioning in CSCW. Both groups were represented at the workshop resulting in an exchange of ideas and information that helped to familiarize developers with the most recent research results in the area, and to provide researchers with an updated view of the needs and challenges faced by application developers. In preparing for this workshop, the organizers were able to build upon the results of their previous one entitled "The Workshop on Versioning in Hypertext" held in conjunction with the ECHT'94 conference. The following section of this report contains a summary in which the workshop organizers report the major results of the workshop. The summary is followed by a section that contains the position papers that were accepted to the workshop. The position papers provide more detailed information describing recent research efforts of the workshop participants as well as current challenges that are being encountered in the development of CSCW applications. A list of workshop participants is provided at the end of the report. The organizers would like to thank all of the participants for their contributions which were, of course, vital to the success of the workshop. We would also like to thank the ECSCW'95 conference organizers for providing a forum in which this workshop was possible

User Defined Prewrites for Increasing Concurrency in Design Databases

We introduce a prewrite operation before a write operation is performed on design databases, a database that consists of objects as engineering designs. A prewrite operation does not actually make a design but it only makes available the model of the design that the transaction will produce in future. Once the prewrite design by a transaction is announced, the transaction executes a pre-commit operation. After the pre-commit, read operations can access the prewrite design even before the pre-committed transaction has finally made the design and committed. Therefore, our algorithm increases the potential concurrency as compared to the algorithms that permit only read and write operations on the design objects. In our algorithm, a user explicitly makes available a prewrite model of the design to be finally produced. Similarly, a read transaction also mentions whether it wants to read a prewrite version or the final version of the design. Locking protocols using two phase locking are given to control concurrent operation

Semantics-based locking:from isolation to cooperation

'Advanced database applications', such as CAD/CAM, CASE, large AI applications or imageand voice processing, place demands on transaction management which differ substantially from those of traditional database applications. In particular, there is a need to support 'enriched' data models (which include, for example, complex objects or version and configuration management), 'synergistic' cooperative work, and application- or user-supported consistency. This paper deals with a subset of these problems. It develops a methodology for implementing semantics-based concurrency control on the basis of ordinary locking. More specifically, it will be shown how conventional locking can step by step be improved and refined to finally reach our initial goal, namely a comprehensive support of synergistic cooperative work by the exploitation of application-specific semantics. In addition to the 'conventional' binding of locks to transactions we consider the binding of locks to objects (object related) and subjects (subject related locks). Object related locks can define persistent and adaptable access restrictions on objects. This permits, among others, the modeling of different types of version models (time versions, version graphs) as well as library (standard) objects. Subject related locks are bound to subjects (user, application, etc.) and can be used among others to supervise or direct the transfer of objects between transactions.<br/

An Integrated Engineering-Computation Framework for Collaborative Engineering: An Application in Project Management

Today\u27s engineering applications suffer from a severe integration problem. Engineering, the entire process, consists of a myriad of individual, often complex, tasks. Most computer tools support particular tasks in engineering, but the output of one tool is different from the others\u27. Thus, the users must re-enter the relevant information in the format required by another tool. Moreover, usually in the development process of a new product/process, several teams of engineers with different backgrounds/responsibilities are involved, for example mechanical engineers, cost estimators, manufacturing engineers, quality engineers, and project manager. Engineers need a tool(s) to share technical and managerial information and to be able to instantly access the latest changes made by one member, or more, in the teams to determine right away the impacts of these changes in all disciplines (cost, time, resources, etc.). In other words, engineers need to participate in a truly collaborative environment for the achievement of a common objective, which is the completion of the product/process design project in a timely, cost effective, and optimal manner. In this thesis, a new framework that integrates the capabilities of four commercial software, Microsoft Excel™ (spreadsheet), Microsoft Project™ (project management), What\u27s Best! (an optimization add-in), and Visual Basic™ (programming language), with a state-of-the-art object-oriented database (knowledge medium), InnerCircle2000™ is being presented and applied to handle the Cost-Time Trade-Off problem in project networks. The result was a vastly superior solution over the conventional solution from the viewpoint of data handling, completeness of solution space, and in the context of a collaborative engineering-computation environment

Optimistic concurrency control revisited

Several years ago optimistic concurrency control gained much attention in the database community. However, two-phase locking was already well established, especially in the relational database market. Concerning traditional database systems most developers felt that pessimistic concurrency control might not be the best solution for concurrency control, but, a well-known and accepted one. With the work on new generation database systems, however, there has been a revival of optimistic concurrency control (at least a partial one). This paper will reconsider optimistic concurrency control. It will lay bare the shortcomings of the original approach and present some major improvements. Moreover, several techniques will be presented which especially support read transactions with the consequence that the number of backups can be decreased substantially. Finally, a general solution for the starvation problem is presented. The solution is perfectly consistent with the underlying optimistic approach

Extended Transaction Models for Software Development Environments

This technical report consists of two papers discussing concurrency control facilities for multiuser software development environments. A Marvelous Extended Transaction Processing Model briefly sketches the previously developed commit-serializability model and then applies it to the MARVEL kernel for software development environments. A Participant Semantics for Serializable Transactions describes our first pass at a different extended transaction model that moves users inside the system, so certain users may participate in transactions and the interactions among transactions while all other users observe only a serial order for the transactions