Mihail F. Ionescu

The DISCIPLE system for collaboration over the heterogeneous Web

With the proliferation of mobile devices we witness an increasing demand for supporting collaboration among users working in the field and in the office. A key component for collaboration in this domain is sharing and manipulation of information using very different display capabilities on the diverse devices. We present a system based on a distributed repository of shared data objects and a client-server based infrastructure. The system is robust to intermittent connections, and a mixture of slow and fast links. To preserve bandwidth, application-specific data distribution agents decide what data to send to the clients. We also present a framework for building collaborative applications for clients with different display and processing capabilities. We describe example applications implemented both as Java applets to run in Web browsers and as Java spotlets to run on Palm OS based handheld computers. Using these applications we evaluated the framework and the results show that the framework is scaleable, offers good performance and has a high degree of code reusability.

Stateful publish-subscribe for mobile environments

The Publish-Subscribe paradigm has become an important architectural style for designing distributed systems. In the recent years, we have been witnessing an increasing demand for supporting publish-subscribe for mobile systems in wireless environments. In this paper we present SUBLIM, a stateful model for publish-subscribe systems, which is suitable for mobile systems. In our system, the server maintains a state for each client, which contains variables that describe the properties of particular clients, such as the quality of the connection or the battery utilization. The interest of each subscriber can be expressed in terms of these variables. Based on the subscriber interests, an associated agent is created on the server. The agent filters the data that reach the subscriber based on the content of the message and the current subscriber state. Experimental results show good performance and scalability of our approach.

Decentralized Peer-to-Peer Auctions

This paper proposes a flexible architecture for the creation of Internet auctions. It allows the custom definition of the auction parameters, and provides a decentralized control of the auction process. Auction policies are defined as laws in the Law Governed Interaction (LGI) paradigm. Each of these laws specifies not only the auction algorithm itself (e.g., open-cry, Dutch, etc.) but also how to handle the other parameters usually involved in the online auctions, such as certification, auditioning, and treatment of complaints. LGI is used to enforce the rules established in the auction policy within the agents involved in the process. After the agents find out about the actions, they interact in a peer-to-peer communication protocol, reducing the role of the centralized auction room to an advertising registry, and taking profit of the distributed nature of the Internet to conduct the auction. The paper presents an example of an auction law, illustrating the use of the proposed architecture.

Tree-Based Concurrency Control inDistributed Groupware

We present a novel algorithm, called dARB, forsolving the concurrency control problem indistributed collaborative applications. Themain issue of concurrency control is resolvingthe conflicts resulting from simultaneousactions of multiple users. The algorithmreduces the need for manual conflict resolutionby using a distributed arbitration scheme. Themain advantages of our approach are thesimplicity of use and good responsiveness, asthere are no lock mechanisms. Our algorithmrequires the applications to use a tree as theinternal data structure. This makes itapplication independent and suitable forgeneral collaborative applications. The treerequirement is reasonable since many newapplications use XML (extensible MarkupLanguage) for data representation and exchange,and parsing XML documents results in treestructures. Example applications of thealgorithm, a group text editor and acollaborative 3D virtual environment calledcWorld, are implemented and evaluated in theDISCIPLE collaboration framework. We alsointroduce awareness widgets that users avoidgenerating the conflicting events and help inmanual conflict resolution.

Law-governed peer-to-peer auctions

This paper proposes a flexible architecture for the creation of Internet auctions. It allows the custom definition of the auction parameters, and provides a decentralized control of the auction process. Auction policies are defined as laws in the Law Governed Interaction (LGI) paradigm. Each of these laws specifies not only the auction algorithm itself (e.g. open-cry, dutch, etc.) but also how to handle the other parameters usually involved in the online auctions, such as certification, auditioning, and treatment of complaints. LGI is used to enforce the rules established in the auction policy within the agents involved in the process. After the agents find out about the actions, they interact in a peer-to-peer communication protocol, reducing the role of the centralized auction room to an advertising registry, and taking profit of the distributed nature of the Internet to conduct the auction. The paper presents an example of an auction law, illustrating the use of the proposed architecture.

Enforcement of Communal Policies for P2P Systems

We consider the question of how to establish and enforce communal policies for peer-to-peer (P2P) communities. Generally, members of each P2P community must conform to an application specific communal policy if the community is to operate smoothly and securely. An open question, however, is how can such communal policies be established reliably and in a scalable manner? While some communities can rely on voluntary compliance with their stated policies, voluntary compliance will not be sufficient for many future P2P applications. We illustrate the nature of policies that must be enforced to be reliable by means of an example of a community that operates like Gnutella, but which is established to exchange more sensitive and critical information than music files. Then, we propose to employ the intrinsically distributed control mechanism called Law-Governed Interaction (LGI) for the scalable enforcement of communal P2P policies. To demonstrate the efficacy of the proposed approach, we show how our example policy can be formulated and enforced under LGI. Finally, we modify an existing open-source Gnutella client to work with LGI and show that the use of LGI incurs little overhead.

Publish-subscribe for mobile environments

The Publish-Subscribe paradigm has become an important architectural style for designing distributed systems. In the recent years, we are witnessing an increasing demand for supporting publish-subscribe for mobile computing devices, where conditions used for filtering the data can depend on the particular state of the subscriber (quality of the connection, space and time locality, device capabilities). In this paper we present a stateful model for publish-subscribe systems, suitable for mobile environments. In our system, the server maintains a state for each client, which contains variables that describe the properties of the particular client, such as the quality of the connection or the display size. The interest of each client can be expressed in terms of these variables. Based on the client interests, an associated agent is created on the server. The agent filters the data that reach the client based on the current client state. Experimental results show good performance and scalability of our approach.