Daniel F. Lieuwen

WebViews: accessing personalized web content and services

The ability to take information, entertainment and e-commerce on the go has great promise. However, the existing Web infrastructure and content were designed for desktop computers and are not well-suited for other types of accesses, e.g., devices that have less processing power and memory, small screens, and limited input facilities, or through wireless data networks with low bandwidth and high latency. Thus, there is a growing need for techniques that provide alternative means to access Web content and services, be it the ability to browse the Web through a wireless PDA or smart phone, or hands-free access through voice interfaces. In this paper, we discuss issues involved in making existing Web content and services available for diverse environments, and describe WebViews, a system that allows casual Web users to easily create customized views of Web sites that are well-suited for di erent types of terminals. In particular, we describe our approach to provide voice access to these Web views and experiences in building the system.

Enabling context-aware and privacy-conscious user data sharing

This paper provides detail on two key components of the Houdini framework under development at Bell Labs, that enable context-aware and privacy-conscious user data sharing appropriate for mobile and/or ubiquitous computing. The framework includes an approach for integrating data from diverse sources, for gathering user preferences for what data to share and when to share it, and a policy management infrastructure in the network for enforcing those preferences. The current paper focuses on two components of this infrastructure that are essential for mobile and ubiquitous computing, namely the framework to support self-provisioning of preferences, and the performance of the underlying rules engine.

Automating Web navigation with the WebVCR

Recent developments in Web technology such as the inclusion of scripting languages, frames, and the growth of dynamic content, have made the process of retrieving Web content more complicated, and sometimes tedious. For example, Web browsers do not provide a method for a user to bookmark a frame-based Web site once the user navigates within the initial frameset. Also, some sites, such as travel sites and online classifieds, require users to go through a sequence of steps and fill out a sequence of forms in order to access their data. Using the bookmark facilities implemented in all popular browsers, often it is not possible to create a shortcut to access such data, and these steps must be manually repeated every time the data is needed. However, hard-to-reach pages are often the best candidates for a shortcut, because significantly more effort is required to reach them than to reach a standard page with a well-defined URL. The WebVCR system addresses this problem by letting users record and replay a series of browsing steps in smart bookmarks— shortcuts to Web content that require multiple steps to be retrieved. It provides a VCR-style interface to transparently record and replay users’ actions. Creating and updating smart bookmarks is a simple process involving only the usual browsing actions and requiring no programming by the user. In addition to saving users time by providing shortcuts to hard-to-reach Web content, smart bookmarks can be used as building blocks for many interesting Web applications and new e-commerce services. In this paper, we describe the WebVCR and the techniques it uses to record and replay smart bookmarks, as well as our experiences in building the system. We also discuss some applications that are simplified/enabled by smart bookmarks.

Supporting multiple view maintenance policies

Materialized views and view maintenance are becoming increasingly important in practice. In order to satisfy different data currency and performance requirements, a number of view maintenance policies have been proposed. Immediate maintenance involves a potential refresh of the view after every update to the deriving tables. When staleness of views can be tolerated, a view may be refreshed periodically or (on-demand) when it is queried. The maintenance policies that are chosen for views have implications on the validity of the results of queries and affect the performance of queries and updates. In this paper, we investigate a number of issues related to supporting multiple views with different maintenance policies. We develop formal notions of consistency for views with different maintenance policies. We then introduce a model based on view groupings for view maintenance policy assignment, and provide algorithms, based on the viewgroup model, that allow consistency of views to be guaranteed. Next, we conduct a detailed study of the performance aspects of view maintenance policies based on an actual implementation of our model. The performance study investigates the trade-offs between different maintenance policy assignments. Our analysis of both the consistency and performance aspects of various view maintenance policies are important in making correct maintenance policy assignments.

Concurrency Control Theory for Deferred Materialized Views

We consider concurrency control problems that arise in the presence of materialized views. Consider a database system supporting materialized views to speed up queries. For a range of important applications (e.g. banking, billing, network managementransactions that access materialized views would like to get some consistency guarantees--if a transaction reads a base relation after an update, and then reads a materialized view derived from the base relation, it expects to see the effect of the base update on the materialized view. If a transaction reads two views, it expects that the two views reflect a single consistent database state. Such guarantees are not easy to obtain, as materialized views become inconsistent upon updates to base relations. Immediate maintenance reestablishes consistency within the transaction that updates the base relation, but this consistency comes at the cost of delaying update transactions. Deferred maintenance has been proposed to avoid penalizing update transactions by shifting maintenance into a different transaction (for example, into the transaction that reads the However, doing so causes a materialized view to become temporarily inconsistent with its definition. Consequently, transactions that read multiple materialized views, or that read a materialized view and also read and/or write base relations may execute in a non-serializable manner even when they are running under a strict two phase locking (2PL) protocol. We formalize the concurrency control problem in systems supporting materialized views. We develop a serializability theory based upon conflicts and serialization graphs in the presence of materialized views. Concurrency control algorithms based on this theory are being developed in the SWORD/Ode database system.z The work of Akira Kawaguchi and Kenneth A. Ross was performed while visiting AT&T Bell Laboratories, and was also partially supported by a grant from the AT&T Foundation, by a David and Lucile Packard Foundatio

Implementing Incremental View Maintenance in Nested Data Models

Previous research on materialized views has primarily been in the context of flat relational databases—materialized views defined in terms of one or more flat relations. This paper discusses a broader class of view definitions-materialized views defined over a nested data model such as the nested relational model or an object-oriented data model. An attribute of a tuple deriving the view can be a reference (i.e., a pointer) to a nested relation, with arbitrary levels of nesting possible. The extended capability of this nested data model, together with materialized views, simplifies data modeling and gives more flexibility.

The Architecture of the Dalí Main-Memory Storage Manager

Performance needs of many database applicationsdictate that the entire database be stored in main memory.The dali system is a main memory storage manager designed toprovide the persistence, availability and safety guarantees one typically expects from a disk-resident database, while at the same time providing very high performance by virtue of being tuned to support in-memory data.User processes map the entire database into their address space andaccess data directly, thus avoiding expensive remote procedure calls andbuffer manager interactionstypical of accesses in disk-resident commercial systems available today.dali recovers the database to a consistent state in the case of system as well as process failures. It alsoprovides unique concurrency control and memory protection features, aswell as ordered and unordered index structures. Both object-oriented and relational database management systems have beenimplemented on top of dali. dali provides access to multiple layers ofapplication programming interface, including its low-level recovery,concurrency control and indexing components as well as its high-levelrelational component. Finally, various features of dali can be tailored tothe needs of an application to achieve high performance–for example,concurrency control and logging can be turned off if not desired, enablingdali to efficiently support applications that requirenon-persistent memory-resident data to be shared by multiple processes.

A transformation-based approach to optimizing loops in database programming languages

Database programming languages like <italic>O</italic><subscrpt>2</subscrpt>, <italic>E</italic>, and <italic>O</italic>++ include the ability to iterate through a set. Nested iterators can be used to express joins. This paper describes compile-time optimizations similar to relational transformations like join reordering for such programming constructs. This paper also shows how to use a standard transformation-based optimizer to optimize these joins. An optimizer built using the EXODUS Optimizer Generator [GRAE87] was added to the Bell Labs <italic>O</italic>++ [AGRA89] compiler. We used the resulting optimizing compiler to experimentally validate the ideas in this paper. The experiments show that this technique can significantly improve the performance of database programming languages.

Performance evaluation of object-oriented active database systems using the BEAST benchmark

This paper uses the BEAST benchmark to present the first serious performance study of object-oriented active database management systems (ADBMS). BEAST stresses the performance-critical components of active systems: event detection, event composition, rule retrieval, and rule firing. Method invocation events and transactional events are taken into account. Four systems, namely ACOOD, NAOS, Ode, and SAMOS, have been tested with the benchmark tests of BEAST. The performance measurements demonstrate achievements in the area of active database technology, but also indicate tradeoffs (e.g. between performance and functionality). Finally, the benchmark identifies optimizations and provides hints to ADBMS desigers about producing systems with adequate performance and functionality --- as well as some open issues.

Subscriber data management in IMS networks

Next-generation communication services will be driven by increasingly rich and distributed subscriber information. Current wireless networks have evolved such that subscriber information now resides in various elements e.g., home location register [HLR], prepay, voice mail, short message, and location determination systems). Convergence with the Internet promises significantly more personal information, such as presence, calendars, address books, buddy lists, pictures, and video. The home subscriber server (HSS) in the IP Multimedia Subsystem (IMS) architecture provides centralized storage for subscriber data. However, some application servers will also have their own subscriber data. As the quantity and variety of applications grow, it will become increasingly useful to provide unified views of subscriber data both within a network and across networks. The Lucent Datagrid™ software provides a telecom-targeted data integration capability, so that applications can use a logical “single-point-of-access” for user profile information inside a service providers network.