Rethinking Consistency Management in Real-time Collaborative Editing Systems

Networked computer systems offer much to support collaborative editing of shared documents among users. Increasing concurrent access to shared documents by allowing multiple users to contribute to and/or track changes to these shared documents is the goal of real-time collaborative editing systems (RTCES); yet concurrent access is either limited in existing systems that employ exclusive locking or concurrency control algorithms such as operational transformation (OT) may be employed to enable concurrent access. Unfortunately, such OT based schemes are costly with respect to communication and computation. Further, existing systems are often specialized in their functionality and require users to adopt new, unfamiliar software to enable collaboration. This research discusses our work in improving consistency management in RTCES. We have developed a set of deadlock-free multi-granular dynamic locking algorithms and data structures that maximize concurrent access to shared documents while minimizing communication cost. These algorithms provide a high level of service for concurrent access to the shared document and integrate merge-based or OT-based consistency maintenance policies locally among a subset of the users within a subsection of the document – thus reducing the communication costs in maintaining consistency. Additionally, we have developed client-server and P2P implementations of our hierarchical document management algorithms. Simulations results indicate that our approach achieves significant communication and computation cost savings. We have also developed a hierarchical reduction algorithm that can minimize the space required of RTCES, and this algorithm may be pipelined through our document tree. Further, we have developed an architecture that allows for a heterogeneous set of client editing software to connect with a heterogeneous set of server document repositories via Web services. This architecture supports our algorithms and does not require client or server technologies to be modified – thus it is able to accommodate existing, favored editing and repository tools. Finally, we have developed a prototype benchmark system of our architecture that is responsive to users’ actions and minimizes communication costs

Request Scheduling for Multiactive Objects

National audienceThe Active Object programming model aims to facilitate the writing of distributed applica- tions. It provides asynchronous remote method calls and mechanisms to prevent data races. However, this model does not take advantage of multicore architectures as it is intrinsically mono-threaded. To overcome this problem, a recent extension of the active object model has been designed, which is called the Multiactive Object model. Multiactive objects enable local parallelism at a high level without giving up simplicity and safety provided by active objects: the programmer can declare which requests can be run in parallel through a customized spec- ification language. However, in this new model, the programmer has not yet control on the scheduling policy applied to the requests executed by a multiactive object. In this work, we study application-level scheduling concepts that can be applied to multiactive objects. The goal is to allow the programmer to have a fine control on the scheduling policy through simple specifications. We first develop a priority mechanism that can be used to reorder awaiting requests in the queue of multiactive objects. Second, we provide a simple thread management mechanism to better allocate available threads to awaiting requests. Finally, we experiment the new features in a practical context, showing that the proposed mechanisms increase the efficiency of multiactive objects while keeping a low overhead. On the whole, we provide gen- eral specifications for application-level scheduling that are together fine-grained, user-friendly, and efficient

Towards Collaborative Scientific Workflow Management System

The big data explosion phenomenon has impacted several domains, starting from research areas to divergent of business models in recent years. As this intensive amount of data opens up the possibilities of several interesting knowledge discoveries, over the past few years divergent of research domains have undergone the shift of trend towards analyzing those massive amount data. Scientific Workflow Management System (SWfMS) has gained much popularity in recent years in accelerating those data-intensive analyses, visualization, and discoveries of important information. Data-intensive tasks are often significantly time-consuming and complex in nature and hence SWfMSs are designed to efficiently support the specification, modification, execution, failure handling, and monitoring of the tasks in a scientific workflow. As far as the complexity, dimension, and volume of data are concerned, their effective analysis or management often become challenging for an individual and requires collaboration of multiple scientists instead. Hence, the notion of 'Collaborative SWfMS' was coined - which gained significant interest among researchers in recent years as none of the existing SWfMSs directly support real-time collaboration among scientists. In terms of collaborative SWfMSs, consistency management in the face of conflicting concurrent operations of the collaborators is a major challenge for its highly interconnected document structure among the computational modules - where any minor change in a part of the workflow can highly impact the other part of the collaborative workflow for the datalink relation among them. In addition to the consistency management, studies show several other challenges that need to be addressed towards a successful design of collaborative SWfMSs, such as sub-workflow composition and execution by different sub-groups, relationship between scientific workflows and collaboration models, sub-workflow monitoring, seamless integration and access control of the workflow components among collaborators and so on. In this thesis, we propose a locking scheme to facilitate consistency management in collaborative SWfMSs. The proposed method works by locking workflow components at a granular attribute level in addition to supporting locks on a targeted part of the collaborative workflow. We conducted several experiments to analyze the performance of the proposed method in comparison to related existing methods. Our studies show that the proposed method can reduce the average waiting time of a collaborator by up to 36% while increasing the average workflow update rate by up to 15% in comparison to existing descendent modular level locking techniques for collaborative SWfMSs. We also propose a role-based access control technique for the management of collaborative SWfMSs. We leverage the Collaborative Interactive Application Methodology (CIAM) for the investigation of role-based access control in the context of collaborative SWfMSs. We present our proposed method with a use-case of Plant Phenotyping and Genotyping research domain. Recent study shows that the collaborative SWfMSs often different sets of opportunities and challenges. From our investigations on existing research works towards collaborative SWfMSs and findings of our prior two studies, we propose an architecture of collaborative SWfMSs. We propose - SciWorCS - a Collaborative Scientific Workflow Management System as a proof of concept of the proposed architecture; which is the first of its kind to the best of our knowledge. We present several real-world use-cases of scientific workflows using SciWorCS. Finally, we conduct several user studies using SciWorCS comprising different real-world scientific workflows (i.e., from myExperiment) to understand the user behavior and styles of work in the context of collaborative SWfMSs. In addition to evaluating SciWorCS, the user studies reveal several interesting facts which can significantly contribute in the research domain, as none of the existing methods considered such empirical studies, and rather relied only on computer generated simulated studies for evaluation

Request Scheduling for Multiactive Objects

National audienceThe Active Object programming model aims to facilitate the writing of distributed applica- tions. It provides asynchronous remote method calls and mechanisms to prevent data races. However, this model does not take advantage of multicore architectures as it is intrinsically mono-threaded. To overcome this problem, a recent extension of the active object model has been designed, which is called the Multiactive Object model. Multiactive objects enable local parallelism at a high level without giving up simplicity and safety provided by active objects: the programmer can declare which requests can be run in parallel through a customized spec- ification language. However, in this new model, the programmer has not yet control on the scheduling policy applied to the requests executed by a multiactive object. In this work, we study application-level scheduling concepts that can be applied to multiactive objects. The goal is to allow the programmer to have a fine control on the scheduling policy through simple specifications. We first develop a priority mechanism that can be used to reorder awaiting requests in the queue of multiactive objects. Second, we provide a simple thread management mechanism to better allocate available threads to awaiting requests. Finally, we experiment the new features in a practical context, showing that the proposed mechanisms increase the efficiency of multiactive objects while keeping a low overhead. On the whole, we provide gen- eral specifications for application-level scheduling that are together fine-grained, user-friendly, and efficient

Shelfaware: Accelerating Collaborative Awareness with Shelf CRDT

Collaboration has become a key feature of modern software, allowing teams to work together effectively in real-time while in different locations. In order for a user to communicate their intention to several distributed peers, computing devices must exchange high-frequency updates with transient metadata like mouse position, text range highlights, and temporary comments. Current peer-to-peer awareness solutions have high time and space complexity due to the ever-expanding logs that each client must maintain in order to ensure robust collaboration in eventually consistent environments. This paper proposes an awareness Conflict-Free Replicated Data Type (CRDT) library that provides the tooling to support an eventually consistent, decentralized, and robust multi-user collaborative environment. Our library is tuned for rapid iterative updates that communicate fine-grained user actions across a network of collaborators. Our approach holds memory constant for subsequent writes to an existing key on a shared resource and completely prunes stale data from shared documents. These features allow us to keep the CRDT\u27s memory footprint small, making it a feasible solution for memory constrained applications. Results show that our CRDT implementation is comparable to or exceeds the performance of similar data structures in high-frequency read/write scenarios

Developing Collaborative XML Editing Systems

In many areas the eXtensible Mark-up Language (XML) is becoming the standard exchange and data format. More and more applications not only support XML as an exchange format but also use it as their data model or default file format for graphic, text and database (such as spreadsheet) applications. Computer Supported Cooperative Work is an interdisciplinary field of research dealing with group work, cooperation and their supporting information and communication technologies. One part of it is Real-Time Collaborative Editing, which investigates the design of systems which allow several persons to work simultaneously in real-time on the same document, without the risk of inconsistencies. Existing collaborative editing research applications specialize in one or at best, only a small number of document types; for example graphic, text or spreadsheet documents. This research investigates the development of a software framework which allows collaborative editing of any XML document type in real-time. This presents a more versatile solution to the problems of real-time collaborative editing. This research contributes a new software framework model which will assist software engineers in the development of new collaborative XML editing applications. The devised framework is flexible in the sense that it is easily adaptable to different workflow requirements covering concurrency control, awareness mechanisms and optional locking of document parts. Additionally this thesis contributes a new framework integration strategy that enables enhancements of existing single-user editing applications with real-time collaborative editing features without changing their source code

Elastic Business Process Management: State of the Art and Open Challenges for BPM in the Cloud

With the advent of cloud computing, organizations are nowadays able to react rapidly to changing demands for computational resources. Not only individual applications can be hosted on virtual cloud infrastructures, but also complete business processes. This allows the realization of so-called elastic processes, i.e., processes which are carried out using elastic cloud resources. Despite the manifold benefits of elastic processes, there is still a lack of solutions supporting them. In this paper, we identify the state of the art of elastic Business Process Management with a focus on infrastructural challenges. We conceptualize an architecture for an elastic Business Process Management System and discuss existing work on scheduling, resource allocation, monitoring, decentralized coordination, and state management for elastic processes. Furthermore, we present two representative elastic Business Process Management Systems which are intended to counter these challenges. Based on our findings, we identify open issues and outline possible research directions for the realization of elastic processes and elastic Business Process Management.Comment: Please cite as: S. Schulte, C. Janiesch, S. Venugopal, I. Weber, and P. Hoenisch (2015). Elastic Business Process Management: State of the Art and Open Challenges for BPM in the Cloud. Future Generation Computer Systems, Volume NN, Number N, NN-NN., http://dx.doi.org/10.1016/j.future.2014.09.00