Real-time Collaborative Systems Research Articles

Integrating selective undo of feature-based modeling operations for real-time collaborative CAD systems

Abstract In collaborative editing systems, selective undo is a fundamental function that allows dispersed users to undo any executed operation in the history. Most selective undo mechanisms have been applied in collaborative editing systems with simple objects (plain text or image). However, how to provide a selective undo mechanism for collaborative editing systems with complex objects (feature-based CAD model) has been a technical challenge. This paper proposes a novel CRDT (Conflict-free Replicated Data Type)-based selective undo mechanism for feature-based Co-CAD (Collaborative CAD) systems. Firstly, a selective undo framework is presented to integrate (do/undo) operations. Secondly, three constraint relations of (do/undo) operations are defined and feature-based conflict detection conditions are proposed to detect the three constraint relations. Thirdly, a CRDT-based conflict resolution approach is proposed to integrate (do/undo) operations. Fourthly, collaborative case studies illustrate how the selective undo mechanism works and achieves consistent results. Finally, the complexities in theory are analyzed and the formal proofs are provided to verify the correctness.

A novel CRDT-based synchronization method for real-time collaborative CAD systems

CRDT (Conflict-free Replicated Data Type) has been proposed as an alternative synchronization mechanism for collaborative text editing systems in recent years. However, CRDT-based synchronization methods for collaborative systems with sophisticated objects, such as collaborative CAD (Co-CAD) systems, are rarely investigated in previous literatures. How well CRDT-based synchronization methods for Co-CAD systems could perform remains unknown. This paper presents a novel CRDT-based synchronization method to maintain eventual consistency for the feature-based CAD model. Firstly, three operation relations are defined as the dependency-conflict relation, the mutual exclusive relation and the compatible relation in context of the feature-based CAD systems. Secondly, a feature-based conflict detection mechanism is proposed to detect the three relations. Thirdly, a feature-based conflict resolution approach under the CRDT framework is presented to solve the conflicts. Fourthly, the time complexity and the space complexity are analyzed in theory. Finally, case studies of collaborative modeling procedures verify the correctness and feasibility of the proposed method.

Meta-operation conflict resolution for human–human interaction in collaborative feature-based CAD systems

Conflicts resolution is one of the key issues in maintaining consistency and in supporting smooth human---human interaction for real-time collaborative systems. This paper presents a novel approach of meta-operation conflict resolution for feature-based collaborative CAD system. Although commutative replicated data type (CRDT) is an emerging technique for conflict resolution, it is not capable of resolving conflicts among meta operations for 3D CAD systems. By defining 3 types of meta operations, this work extends CRDT capability to meta operation conflict resolution from 1D to 3D applications. The paper defines the dependency, casuality, conflict and compatible relations specific for 3D collaborative CAD systems. The conflicts of feature-based operations are automatically detected by tracking topological entity changes with the assistance of a persistent data structure, topological entity structure tree ($$TES\_Tree$$TES_Tree). An efficient commutativity-based confliction combination method is proposed to preserve the design intention of each user in a transparent way and maintains the eventual consistent state of the system. The proposed methods are tested in a prototype system with case studies, time complexity analysis and correctness proof.

Consistency maintenance of Do and Undo/Redo operations in real-time collaborative bitmap editing systems

In real-time collaborative graphical editing systems, bitmap-based graphical editing systems are particularly special and practically useful ones, and Do and Undo/Redo operations are intricate problems in this field. However, existing researches on graphical editing systems are quite scanty. In this paper, based on Multi-version strategy, we propose a new approach to solve the Do and Undo/Redo consistency maintenance problems with due consideration of three possible cases: all-causal, all-independent and causal-independent-mixed operations. Compared with previous collaborative algorithms, the algorithms proposed in this paper support Do and Undo/Redo operations without requiring additional space. In addition, two example analyses are also given to prove the algorithms' effectiveness separately. Furthermore, the time complexity of the two algorithms is both O(n). Finally, a system prototype called bitmap-based Co-Graphical Editor is implemented to verify them realistically.

Consistency Maintenance of Group/Ungroup Operations in Object-based Collaborative Graphical Editing Systems

In real-time collaborative graphical editing systems, Object-based Group/Ungroup operations are frequently accessible and practically useful. However, the existing research on these operations of the graphical editing is rare and defective. In this paper, based on Multi-Version strategy and Address Space Transformation method, a new MVSDR algorithm, which is not only applied to simple operations (such as Create, Delete, ChangeATT, etc.), but also suitable for Group/Ungroup ones, is proposed to solve the consistency maintenance problem. The proposed algorithm abandons previous attempts to divide conflict operations into Real-Conflict operations and Resolvable-Conflict ones and to deal with them separately, thus making the algorithm more simple and effective. In addition, an example analysis is also given in this paper to prove the algorithm’s correctness and effectiveness.

Consistency maintenance in real-time collaborative graphics editing systems

The following abstracts are from recent issues and the forthcoming issue of ACM's Transactions of Computer Human Interaction (ToCHI). They are included here to alert interactions' readers to what research is being done in the field of Computer Human Interaction. The complete papers, when published, can be found in ACM's Digital Library at www.acm. org/pubs/contents/journals/tochi/2002-9/#1.

Consistency maintenance in real-time collaborative graphics editing systems

Real-time collaborative graphics editing systems allow a group of users to view and edit the same graphics document at the same time from geographically dispersed sites connected by communication networks. Consistency maintenance in the face of concurrent accesses to shared objects is one of the core issues in the design of these types of systems. In this article, we propose an object-level multiversioning approach to consistency maintenance in real-time collaborative graphic editors. This approach is novel in achieving intention preservation and convergence, in preserving the work concurrently produced by multiple users in the face of conflict, and in minimizing the number of object versions for conflict resolution. Major technical contributions of this work include a formal specification of a unique combined effect for an arbitrary group of conflict and compatible operations, a distributed algorithm for incremental creation of multiple object versions, a consistent object identification scheme for multiple object versions, and a convergent layering scheme for overlapping objects. All algorithms and schemes presented in this article have been implemented in an Internet-based GRACE (graphics collaborative editing) system.

Real-time collaboration in design engineering: An expensive fantasy or affordable reality?

The purpose of this paper is to discuss the main issues that are both driving and impeding the implementation and use of CSCW systems within the automotive industry. The paper begins by describing the current competitive pressures within the European Automotive industry and then moves on to highlight the main requirements for real-time collaborative systems, as expressed by various organizations along the automotive supply chain. Finally, the paper presents the results of a recent project in this area and some conclusions on the viability of CSCW technology in the current technical and commercial climate.