Introducing Selective Undo Features in a Collaborative Editor

Undo is an important functionality of editors. Selective undo is widely regarded as an important feature for collaborative editing. However, even after nearly three decades of active research and development, there is still no practical support of selective undo for collaborative editing. This paper introduces the selective undo features that we have implemented as part of a collaborative editing subsystem in the GNU Emacs text editor

A Generic Undo Support for State-Based CRDTs

CRDTs (Conflict-free Replicated Data Types) have properties desirable for large-scale distributed systems with variable network latency or transient partitions. With CRDT, data are always available for local updates and data states converge when the replicas have incorporated the same updates. Undo is useful for correcting human mistakes and for restoring system-wide invariant violated due to long delays or network partitions. There is currently no generally applicable undo support for CRDTs. There are at least two reasons for this. First, there is currently no abstraction that we can practically use to capture the relations between undo and normal operations with respect to concurrency and causality. Second, using inverse operations as the existing partial solutions, the CRDT designer has to hard-code certain rules and design a new CRDT for almost every operation that needs undo support. In this paper, we present an approach to generic support of undo for CRDTs. The approach consists of two major parts. We first work out an abstraction that captures the semantics of concurrent undo and redo operations through equivalence classes. The abstraction is a natural extension of undo and redo in sequential applications and is straightforward to implement in practice. By using this abstraction, we then device a mechanism to augment existing CRDTs. The mechanism provides an "out of the box" support for undo without the involvement of the CRDT designers. We also present a practical application of the approach in collaborative editing

Conflict-Free Replicated Relations for Multi-Synchronous Database Management at Edge

International audienceIn a cloud-edge environment, edge devices may not always be connected to the network. Still, applications may need to access the data on edge devices even when they are not connected. With support for multi-synchronous access, data on an edge device are kept synchronous with the data in the cloud as long as the device is online. When the device is off-line, the application can still access the data on the device, asynchronously with concurrent data updates either in the cloud or on other edge devices. Conflict-free Replicated Data Types (CRDTs) emerged as a technology for multi-synchronous data access. CRDTs guarantee that when all sites have applied the same set of updates, the replicated data converge. However, CRDTs have not been successfully applied to relational databases (RDBs) for multi-synchronous access. In this paper, we present Conflict-free Replicated Relations (CRRs) that apply CRDTs to RDBs for support of multi-synchronous data access. With CRR, existing RDB applications, with very little modification, can be enhanced with multi-synchronous access. We also present a prototype implementation of CRR with some preliminary performance results

Feedback Stabilization for a Class of Nonlinear Stochastic Systems with State- and Control-Dependent Noise

This paper mainly studies the state feedback stabilizability of a class of nonlinear stochastic systems with state- and control-dependent noise. Some sufficient conditions on local and global state feedback stabilizations are given in linear matrix inequalities (LMIs) and generalized algebraic Riccati equations (GAREs). Some obtained results improve the previous work

A CRDT Supporting Selective Undo for Collaborative Text Editing

International audienceUndo is an important feature of editors. However, even after over two decades of active research and development, support of undo for real-time col-laborative editing is still very limited. We examine issues concerning undo in collaborative text editing and present an approach using a layered commutative replicated data type (CRDT). Our performance study shows that it provides sufficient responsiveness to the end users

Robust Stability, Stabilization, and H

This paper studies robust stability, stabilization, and H∞ control for a class of nonlinear discrete time stochastic systems. Firstly, the easily testing criteria for stochastic stability and stochastic stabilizability are obtained via linear matrix inequalities (LMIs). Then a robust H∞ state feedback controller is designed such that the concerned system not only is internally stochastically stabilizable but also satisfies robust H∞ performance. Moreover, the previous results of the nonlinearly perturbed discrete stochastic system are generalized to the system with state, control, and external disturbance dependent noise simultaneously. Two numerical examples are given to illustrate the effectiveness of the proposed results

Non-invasive assessment of intracranial wall shear stress using high-resolution magnetic resonance imaging in combination with computational fluid dynamics technique

In vivo studies on association between wall shear stress (WSS) and intracranial plaque are deficient. Based on the three-dimensional T1-weighted high-resolution magnetic resonance imaging (3DT1 HR-MRI) data of patients with low-grade stenotic (<50%) atherosclerotic middle cerebral artery (MCA) and subjects with normal MCA, we built a three-dimensional reconstructed WSS model by computational fluid dynamics (CFD) technique. Three-dimensional registration of the CFD model to the HR-MRI was performed with projections based on the resolution and thickness of the images. The relationships between the WSS at each side of the vessel wall and plaque location were analyzed. A total of 94 MCA plaques from 43 patients and 50 normal MCAs were analyzed. In the normal MCAs, WSS was lower at the ventral-inferior wall than at the dorsal-superior wall (proximal segment, p < 0.001; middle segment, p < 0.001) and lower at the inner wall than at the outer wall of the MCA curve (p < 0.001). In atherosclerotic MCAs, similar low WSS regions were observed where plaques developed. The WSS ratio of the ventral-inferior wall to the dorsal-superior wall in atherosclerotic MCAs was lower than that in normal MCAs (p = 0.002). The WSSinner-outer ratio in atherosclerotic MCAs was lower than that in normal MCAs (p = 0.002). Low WSS was associated with MCA atherosclerosis formation and occurred mainly at the ventral-inferior wall, which was anatomically opposite the orifices of penetrating arteries, and at the inner wall of the MCA curve. Overall, the results were well consistent with the low WSS theory in atherosclerosis formation. The reconstructed WSS model is a promising novel method for assessing an individualized vascular profile once validated by further studies