On the Performance of Flooding-Based Resource Discovery

We consider flooding-based resource discovery in distributed systems. With flooding, a node searching for a resource contacts its neighbors in the network, which in turn contact their own neighbors and so on until a node possessing the requested resource is located. Flooding assumes no knowledge about the network topology or the resource distribution thus offering an attractive means for resource discovery in dynamically evolving networks such as peer-to-peer systems. We provide analytical results for the performance of a number of flooding-based approaches that differ in the set of neighbors contacted at each step. The performance metrics we are interested in are the probability of locating a resource and the average number of steps and messages for doing so. We study both uniformly random resource requests and requests in the presence of popular (hot) resources. Our analysis is also extended to take into account the fact that nodes may become unavailable either due to failures or voluntary departures from the system. Our analytical results are validated through simulation     

YmalDB: exploring relational databases via result-driven recommendations

The typical user interaction with a database system is through queries. However, many times users do not have a clear understanding of their information needs or the exact content of the database. In this paper, we propose assisting users in database exploration by recommending to them additional items, called Ymal (“You May Also Like”) results, that, although not part of the result of their original query, appear to be highly related to it. Such items are computed based on the most interesting sets of attribute values, called faSets, that appear in the result of the original query. The interestingness of a faSet is defined based on its frequency in the query result and in the database. Database frequency estimations rely on a novel approach of maintaining a set of representative rare faSets. We have implemented our approach and report results regarding both its performance and its usefulness.     

Locating objects in mobile computing

In current distributed systems, the notion of mobility is emerging in many forms and applications. Mobility arises naturally in wireless computing since the location of users changes as they move. Besides mobility in wireless computing, software mobile agents are another popular form of moving objects. Locating objects, i.e., identifying their current location, is central to mobile computing. We present a comprehensive survey of the various approaches to the problem of storing, querying, and updating the location of objects in mobile computing. The fundamental techniques underlying the proposed approaches are identified, analyzed, and classified along various dimensions     

Mobile agents for World Wide Web distributed database access

The popularity of the Web as a universal access mechanism for network information has created the need for developing Web-based DBMS client/server applications. However, the current commercial applet-based approaches for accessing database systems offer limited flexibility, scalability, and robustness. We propose a new framework for Web-based distributed access to database systems based on Java-based mobile agents. The framework supports lightweight, portable, and autonomous clients as well as operation on slow or expensive networks. The implementation of the framework using the aglet workbench shows that its performance is comparable to, and in some case outperforms, the current approach. In fact, in wireless and dial-up environments and for average size transactions, a client/agent/server adaptation of the framework provides a performance improvement of approximately a factor of ten. For the fixed network, the gains are about 40 percent and 30 percent, respectively. We expect our framework to perform even better when deployed using different implementation platforms as indicated by our preliminary results from an implementation based on Voyager     

Managing contextual preferences

To handle the overwhelming amount of information currently available, personalization systems allow users to specify through preferences which pieces of data interest them. Most often, users have different preferences depending on context. In this paper, we introduce a model for expressing such contextual preferences. Context is modeled using a set of hierarchical attributes, thus allowing context specification at various levels of detail. We formulate the context resolution problem as the problem of selecting appropriate preferences based on context for personalizing a query. We also propose algorithms for context resolution based on data structures that index preferences by exploiting the hierarchical nature of the context attributes. Finally, we evaluate our approach from two perspectives: usability and performance. Usability evaluates the overheads imposed on users for specifying context-dependent preferences, as well as their satisfaction from the quality of the results. Our performance results focus on the context resolution using the proposed indexes.     

Recommending packages with validity constraints to groups of users

The success of recommender systems has made them the focus of a massive research effort in both industry and academia. Recent work has generalized recommendations to suggest packages of items to single users, or single items to groups of users. However, to the best of our knowledge, the interesting problem of recommending a package to a group of users (P2G) has not been studied to date. This is a problem with several practical applications, such as recommending vacation packages to tourist groups, entertainment packages to groups of friends or sets of courses to groups of students. In this paper, we formulate the P2G problem, and we propose probabilistic models that capture the preference of a group toward a package, incorporating factors such as user impact and package viability. We also investigate the issue of recommendation fairness. This is a novel consideration that arises in our setting, where we require that no user is consistently slighted by the item selection in the package. In addition, we study a special case of the P2G problem, where the recommended items are places and the recommendation should consider the current locations of the users in the group. We present aggregation algorithms for finding the best packages and compare our suggested models with baseline approaches stemming from previous work. The results show that our models find packages of high quality which consider all special requirements of P2G recommendation.     

Sequential group recommendations based on satisfaction and disagreement scores

Journal of Intelligent Information Systems - Recently, group recommendations have gained much attention. Nevertheless, most approaches consider only one round of recommendations. However, in a...     

Providing Database Interoperability through Object-Oriented Language Constructs

Seamless access to resources and services provided by distributed, autonomous, and heterogeneous systems is central to many advanced applications. Building an integrated system to provide such uniform access and cooperation among underlying heterogeneous systems is both an increasing necessity and a formidable challenge. An important component of such a complex integrated system is a unified language that serves both as a data definition and as a data manipulation tool. Special requirements are posed in the instance of an integrated system which includes database systems among its components. In this paper, we introduce the necessary constructs that an object-oriented programming language should provide for being adopted as the language of the integrated system in such a setting. We adopt a modular, object-based approach to integration. Each component system that joins the integration provides a set of basic classes and pre-defined basic methods. We show how the class hierarchy of the system can be used to provide a uniform way of mapping database resources to basic classes and associative queries to basic methods. A view mechanism is introduced that supports the integration of the basic classes and provides a means of expressing relationships among them and resolving any potential conflicts. The view mechanism is implemented by extending the standard class constructors of an object-oriented language to support the definition of virtual classes. The language provides workflow constructs for defining the structure of programs and for attaining synchronization among concurrently executing programs. Furthermore, atomicity and concurrency control information is included in the form of consistency assertions as part of the interface of each basic method.