Henrique João L. Domingos

Integrating synchronous and asynchronous interactions in groupware applications

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.

Reservations for Conflict Avoidance in a Mobile Database System

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.

Mobile Transaction Management in Mobisnap

In this paper we describe a transaction management system designed to face the inherent characteristics of mobile environments. Mobile clients cache subsets of the database state and allow disconnected users to perform transactions independently. Transactions are specified as mobile transactional programs that are propagated and executed in the server, thus allowing the validation of transactions based on application-specific semantics. In the proposed model (as in others previously presented in literature) the final result of a transaction is only determined when the transaction is processed in the central server. Users may be notified of the results of their transactions using system support (even when they are no longer using the same application or even the same computer). Additionally, the system implements a reservation mechanism in order to guarantee the results of transactions performed in disconnected computers.

Flexible data storage for mobile computing

In this paper we describe a flexible object storage system aimed at supporting collaborative applications in large-scale environments that include mobile computers. We present an integrated solution to two major problems that arise in such environments: data availability and concurrency control. The first is tackled by the flexible combination of weakly consistent server replication and client caching. The second is tackled through an open object framework that enables easy object development using type specific conflict detection and resolution. This object storage serves as a supporting platform to produce new distributed and mobile collaborative

SUPPORTING MULTI-SYNCHRONOUS GROUPWARE: DATA MANAGEMENT PROBLEMS AND A SOLUTION

It is common that, in a long-term asynchronous collaborative activity, groups of users engage in occasional synchronous sessions. In this paper, we analyze the data management requirements for supporting this common work practice in typical collaborative activities and applications. We call the applications that support such work practice multi-synchronous applications. This analysis shows that, as users interact in different ways in each setting, some applications have different requirements and need to rely on different data sharing techniques in synchronous and asynchronous settings. 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.

A flexible object-group-oriented framework to support large scale collaborative applications

Recent results of distributed systems research in multicasting and group oriented communication systems and protocols, are very attractive to implement multiparticipant and collaborative applications. We examine the requirements and criteria placed by large scale cooperative applications, namely those alternating multiparticipant synchronous work sessions with asynchronous interactions and disconnected work. We propose a topology organization, an architectural model and the materialization of an integrated generic platform to support those requirements. We argue about the necessary evolution from the well known client/server model to new paradigms involving collaborative-object-group orientation. We describe the implementation of an object-group-oriented infrastructure as well as a generic programming framework offering high flexibility.

Coordination support for scalable collaborative work

In this paper we discuss the principles, design options and implementation issues to support coordination and awareness services in the context of scalable CSCW sessions. We analyze essential differences between the coordination support needed by these sessions when compared with the conventional coordination activity within workflow systems. Then we propose a flexible support model, which is more adequate for group-oriented collaborative work tasks developed in the context of a more complex workgroup activity. The support is concerned with a set of adaptable mechanisms as well as system base components and services provided by an integrated, open and extensible support platform. These components implement a set of facilities for coordination and awareness control in the context of collaboration sessions.

Position summary: supporting disconnected operation in DOORS

The increasing popularity of portable computers opens the possibility of collaboration among multiple distributed and disconnected users. In such environments, collaboration is often achieved through the concurrent modification of shared data. DOORS is a distributed object store to support asynchronous collaboration in distributed systems that may contain disconnected computers. In this summary we focus on the mechanisms to support disconnected operation. The DOORS architecture is composed by servers that replicate objects using an epidemic propagation model. Clients cache key objects to support disconnected operation. Users run applications to read and modify the shared data (independently from other users)-a read any/write any model of data access is used. Modifications are propagated from clients to servers and among servers as sequences of operations-the system is log-based. Objects are structured according to an object framework that decomposes object operation in several components. Each component manages a different aspect of object execution. Each object represents a data type (e.g. a structured document) and it is composed by a set of sub-objects. Each sub-object represents a subpart of the data type (e.g. sections). A new object is created composing the set of subobjects that store the type-specific data with the adequate implementations of the other components. The following main characteristics are the base to support disconnected operation in DOORS.