Hubert Pham

Structured Decomposition of Adaptive Applications

We describe an approach to automate certain high- level implementation decisions in a pervasive application, allowing them to be postponed until run time. Our system enables a model in which an application programmer can specify the behavior of an adaptive application as a set of open-ended decision points. We formalize decision points as goals, each of which may be satisfied by a set of scripts called Techniques. The set of Techniques vying to satisfy any goal is additive and may be extended at runtime without needing to modify or remove any existing techniques. Our system provides a framework in which Techniques may compete and interoperate at runtime in order to maintain an adaptive application. Technique development may be distributed and incremental, providing a path for the decentralized evolution of applications. Benchmarks show that our system imposes reasonable overhead during application startup and adaptation.

A dynamic platform for runtime adaptation

We present a middleware platform for assembling pervasive applications that demand fault-tolerance and adaptivity in distributed, dynamic environments. Unlike typical adaptive middleware approaches, in which sophisticated component model semantics are embedded into an existing, underlying platform (e.g., CORBA, COM, EJB), we propose a platform that imposes minimal constraints for greater flexibility. Such a tradeoff is advantageous when the platform is targeted by automatic code generators that inherently enforce correctness by construction. Applications are written as simple, single-threaded programs that assemble and monitor a set of distributed components. The approach decomposes applications into two distinct layers: (1) a distributed network of interconnected modules performing computations, and (2) constructor logic that assembles that network via a simple block-diagram construction API. The constructor logic subsequently monitors the configured system via a stream of high-level events, such as notifications of resource availability or failures, and consequently provides a convenient, centralized location for reconfiguration and debugging. The component network is optimized for performance, while the construction API is optimized for ease of assembly.

User interface models for the cloud

The current desktop metaphor is unsuitable for the coming age of cloud-based applications. The desktop was developed in an era that was focused on local resources, and consequently its gestures, semantics, and security model reflect heavy reliance on hierarchy and physical locations. This paper proposes a new user interface model that accounts for cloud applications, incorporating representations of people and new gestures for sharing and access, while minimizing the prominence of location. The models key feature is a lightweight mechanism to group objects for resource organization, sharing, and access control, towards the goal of providing simple semantics for a wide range of tasks, while also achieving security through greater usability.

Reducing configuration overhead with goal-oriented programming

The rapid increase in the number and variety of consumer-level electronic devices without the corresponding development of device management technology has lead to a configuration nightmare. We propose to use goal-oriented programming over a substrate of network-portable objects to help reduce the amount of configuration users must do in order to have their applications use their devices efficiently. We detail an architecture and describe a prototype system using existing pervasive computing technology that plays music on the most appropriate devices without requiring user interaction and configuration

Interactive streaming of structured data

We present ChunkStream, a system for efficient streaming and interactive editing of online video. Rather than using a specialized protocol and stream format, ChunkStream makes use of a generic mechanism employing chunks. Chunks are fixed-size arrays that contain a mixture of scalar data and references to other chunks. Chunks allow programmers to expose large, but fine-grained, data structures over the network. ChunkStream represents video clips using simple data types like linked lists and search trees, allowing a client to retrieve and work with only the portions of the clips that it needs. ChunkStream supports resource-adaptive playback and “live” streaming of real-time video as well as fast, frame-accurate seeking; bandwidth-efficient high-speed playback; and compilation of editing decisions from a set of clips. Benchmarks indicate that ChunkStream uses less bandwidth than HTTP Live Streaming while providing better support for editing primitives.

Clui: a platform for handles to rich objects

On the desktop, users are accustomed to having visible handles to objects that they want to organize, share, or manipulate. Web applications today feature many classes of such objects, like flight itineraries, products for sale, people, recipes, and businesses, but there are no interoperable handles for high-level semantic objects that users can grab. This paper proposes Clui, a platform for exploring a new data type, called a Webit, that provides uniform handles to rich objects. Clui uses plugins to 1) create Webits on existing pages by extracting semantic data from those pages, and 2) augmenting existing sites with drag and drop targets that accept and interpret Webits. Users drag and drop Webits between sites to transfer data, auto-fill search forms, map associated locations, or share Webits with others. Clui enables experimentation with handles to semantic objects and the standards that underlie them.

Vision: a lightweight computing model for fine-grained cloud computing

Cloud systems differ fundamentally in how they offer and charge for resources. While some systems provide a generic programming abstraction at coarse granularity, e.g., a virtual machine rented by the hour, others offer specialized abstractions with fine-grained accounting on a per-request basis. In this paper, we explore Tasklets, an abstraction for instances of short-duration, generic computations that migrate from a host requiring computation to hosts that are willing to provide computation. Tasklets enable fine-grained accounting of resource usage, enabling us to build infrastructure that supports trading computing resources according to various economic models. This computation model is especially attractive in settings where mobile devices can utilize resources in the cloud to mitigate local resource constraints.

PerViz: Painkillers for pervasive application debugging

Debugging pervasive applications is difficult due to their distributed, asynchronous, and dynamic nature. To help ease the debugging process, we propose PerViz, a developer-targeted tool that enhances system visibility through real-time visualizations of system state, semi-automates application restarts and positioning, and enables both real-time and asynchronous collaboration in debugging between developers. Developers interact with PerViz through a web browser, which provides a convenient, centralized location to study and filter aggregated application debugging logs and state. In our experience with using PerViz, we have found its log aggregation and real-time visualizations to be key facilitators for effective debugging.

Cloudtop: a workspace for the cloud

Even as users rely more on the web for their computing needs, they continue to depend on a desktop-like area for quick access to in-use resources. The traditional desktop is file-centric and prone to clutter, making it suboptimal for use in a web-dominated world. This paper introduces Cloudtop, a browser plugin that offers a lightweight workplace for temporary items, optimized around the idea that its contents originate from and will ultimately return to the web. Cloudtop improves upon the desktop by 1) implementing a simple, time-based notebook metaphor for managing clutter, 2) capturing and bundling extensible metadata for web resources, and 3) providing a platform for greater interface uniformity across sites.