Geo-replicated storage systems are at the core of current Internet services. The designers of the replication protocols used by these systems must choose between either supporting low-latency, eventually-consistent operations, or ensuring strong consistency to ease application correctness. We propose an alternative consistency model, Explicit Consistency, that strengthens eventual consistency with a guarantee to preserve specific invariants defined by the applications. Given these application-specific invariants, a system that supports Explicit Consistency identifies which operations would be unsafe under concurrent execution, and allows programmers to select either violation-avoidance or invariant-repair techniques. We show how to achieve the former, while allowing operations to complete locally in the common case, by relying on a reservation system that moves coordination off the critical path of operation execution. The latter, in turn, allows operations to execute without restriction, and restore invariants by applying a repair operation to the database state. We present the design and evaluation of Indigo, a middleware that provides Explicit Consistency on top of a causally-consistent data store. Indigo guarantees strong application invariants while providing similar latency to an eventually-consistent system in the common case.

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Putting consistency back into eventual consistency

Architecture for a scalable, pluggable multi-party, and distributed multimedia conferencing. A centralized policy and control conferencing component allows the seamless plug-in of different distributed media components (e.g., data, audio/video, messaging) to accommodate client participation in a conference session. The centralized conference control component includes the following: a conference notification service for accepting subscriptions to the conference state and notifying subscribers about changes to that state; a conference policy and roster control service for storing and manipulating conference policy and rosters; a security service for user authorization/authentication based on user identity information; a scheduling service for conference scheduling; an allocation service for allocating the most available media component(s) for a conference session; and, an MCU management service for conference policy and roster management of the distributed media components.

Distributable, scalable, pluggable conferencing architecture

Putting the Consistency Back Into Eventual Consistency

A system and method for editing images. Each image editing operation is described by a few parameters. Multiple users can share image processing changes by sharing a few set of parameters instead of the whole bitmaps of the images. An Editing List describes the parameters defining the image changes. The size of Editing List is very small and is ideal for network transmission and collaboration. Image Editing Lists are independent of the images themselves. By decoupling the Image Editing Lists from the original bitmap images, other advantages are obtained. For instance, the same Editing List can be applied to other images and also to multiple images at the same time. Rendering of the modified images can be performed at a later time and only when necessary. In case of collaborative editing, the transmission time is reduced drastically.

System and method for image editing

An event-based system and process for recording and playback of collaborative electronic presentations is presented. The present system and process includes a technique for recording collaborative electronic presentations by capturing and storing the interactions between each participant and presentation data where each interaction event is timestamped and linked to a data file comprising the presentation data. The present system and process also includes a technique for playing back the recorded collaborative electronic presentation, which involves displaying the presentation data in an order it was originally presented and reproducing the recorded interactions between each participant and the displayed presentation data at the same point in the presentation that they were originally performed, based on the aforementioned timestamps.

Event-based system and process for recording and playback of collaborative electronic presentations

In asynchronous collaborative applications, users usually collaborate accessing and modifying shared information independently. We have designed and implemented a replicated object store to support such applications in distributed environments that include mobile computers. Unlike most data management systems, awareness support is integrated in the system. To improve the chance for new contributions, the system provides high data availability. The development of applications is supported by an object framework that decomposes objects in several components, each one managing a different aspect of object "execution". New data types may be created relying on pre-defined components to handle concurrent updates, awareness information, etc.

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Data management support for asynchronous groupware

Mobile computing characteristics demand data management systems to support independent operation. However, the execution of updates in a mobile client usually need to be considered tentative because uncoordinated updates that conflict need to be reconciled. In this paper we present a mechanism to independently guarantee that updates can be executed in the server without conflicts. To this end, clients obtain leased reservations upon the database state. Updates are specified as common small PL/SQL programs, dubbed mobile transactions, that execute both in the mobile client and in the server. Using the available reservations, the client transparently verifies that a transaction can be executed in the same way both in the mobile client and in the server, thus leading to the same final result. Mobile transactions may specify conflict detection and resolution rules to be used when transactions cannot be locally guaranteed.

Reservations for Conflict Avoidance in a Mobile Database System

It is common that, in a long-term asynchronous collaborative activity, groups of users engage in occasional synchronous sessions. In this paper, we discuss the data management requirements for supporting this common work practice. As users interact in different ways in each setting, requirements and solutions often need to be different. We present a data management system that allows to integrate a synchronous session in the context of a long-term asynchronous interaction, using the suitable data sharing techniques in each setting and an automatic mechanism to convert the long sequence of small updates produced in a synchronous session into a large asynchronous contribution. We exemplify the use of our approach with two multi-synchronous applications.

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Integrating synchronous and asynchronous interactions in groupware applications

In this technical report we describe a storage system aimed on supporting collaborative applications in large-scale environments that include mobile computers. To maximize availability, it uses weakly consistent server replication and client caching with a read any/write any model of data access. To allow easy management of concurrent updates it provides an object framework that isolates the programmer from the inherent complexity of data replication through code reuse. Type and situation specific conflict detection and resolution are implemented based on support provided by the system and the object framework.

/pdf/system-support-for-large-scale-collaborative-applications-3yxs3ivk15.pdf

System Support for Large-Scale Collaborative Applications

In this paper, we describe a case study of the design and development of a group-conferencing tool suite, built on top of an overlay network based event dissemination framework, which is extensible via quality of service template plug-ins We explain, for each of the tools, how the framework built-in conveniences were explored to create simple but effective distributed solutions, backed by the appropriate quality of service templates, whose design we also discuss

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J. Legatheaux Martins

Papers

Data management support for asynchronous groupware

Reservations for Conflict Avoidance in a Mobile Database System

Integrating synchronous and asynchronous interactions in groupware applications

System Support for Large-Scale Collaborative Applications

A case study on event dissemination in an active overlay network environment