Apratim Purakayastha

Composing pervasive data using iQL

The emergence of pervasive networked data sources, such as Web services, sensors, and mobile devices, enables context-sensitive, mobile applications. We have developed a programming model for writing such applications, in which entities called composers accept data from one or more sources, and act as sources of higher-level data. We have defined and implemented a nonprocedural language, iQL, specifying the behavior of composers. An iQL programmer expresses requirements for data sources rather than identifying specific sources; a runtime system discovers appropriate data sources, binds to them, and rebinds when properties of data sources change. The language has powerful operators useful in composition, including operators to generate, filter, and abstract streams of values.

iQueue: a pervasive data composition framework

There will soon be a huge number of data sources accessible to applications across the Internet. These include Web services, personal devices such as cellular phones and cars, and sensors measuring physical phenomena. New classes of data-composition applications can exploit this data. However, the data is diverse, voluminous, and often rapidly changing. The sources of data can be mobile, distributed, and failure-prone. Without system support, applications that use this kind of data are difficult to write. The iQueue data composition framework provides system support for data composition, thereby making the task of writing applications easier.

Exploiting non-determinism for reliability of mobile agent systems

An important technical hurdle blocking the adoption of mobile agent technology is the lack of reliability. Designing a reliable mobile agent system is especially challenging since a mobile agent is potentially affected by failure of any host that it visits, or failure of any communication link that it needs to traverse. Previous work in this domain has attempted techniques such as periodic checkpointing of mobile agent state and restarting upon machine or communication recovery. Such approaches render an agent unavailable until a machine or a communication link itself recovers. In this paper, we take an alternate approach based on the premise that a mobile agent can often complete its task in more than one way. We capture such redundancy in non-deterministic constructs in the agent language and maintain state about an agents actual computational path in its possible computational tree. We design and implement a distributed recovery scheme that detects a failure, rolls back an agents computation, and restarts the agent from a previous point in its computational tree down a different but equivalent computational path without waiting for the actual failure itself to be repaired.

Enterprise data access from mobile computers: an end-to-end story

Currently, hand-held and palmtop computers are widely used for personal information management. In the near future, they will also be used to access enterprise data. There are however, numerous technical challenges in enabling an end-to-end system that provides enterprise data access from mobile computers. The challenges include heterogeneity, various resource constraints, scalability and security. In this paper, we describe the design and implementation of the Mobile Data Synchronization Service (MDSS), an end-to-end system that provides enterprise data access from mobile computers. Specifically, we address the heterogeneity of devices and data sources, the memory and power constraints of devices, the poor quality of communication and the need for scalability. Our system achieves interoperability and solves the key technical challenges related to enterprise data access from mobile computers.

On demand web-client technologies

This paper describes a comprehensive set of technologies that enables rich interaction paradigms for Web applications. These technologies improve the richness of user interfaces and the responsiveness of user interactions. Furthermore, they support disconnected or weakly connected modes of operation. The technologies can be used in conjunction with many Web browsers and client platforms, interacting with a J2EE™ server. The approach is based on projecting the server-side model-view-controller paradigm onto the client. This approach is firmly rooted in the Web paradigm and proposes a series of incremental extensions. Most of the described technologies have been adopted by IBM server (WebSphere®) and client products.

Mobiscope: A Scalable Spatial Discovery Service for Mobile Network Resources

Mobiscope is a discovery service where clients submit long-running queries to continually find sets of moving network resources within a specified area. As in moving object databases (MODBMSs), moving resources advertise their positions as functions over time. When Mobiscope receives a query, it runs the query statically against advertisements (ads) that are currently cached by Mobiscope, and then continuously over ads that Mobiscope receives subsequently. For scalability, Mobiscope distributes the workload to multiple nodes by spatial coordinates. Application-level routing protocols based on geography ensure that all queries find all matching resources on any node without significant processing overhead. Simulation results indicate that Mobiscope scales well, even under workloads that stress Mobiscopes distribution model.

A programming framework for mobilizing enterprise applications

Mobile applications often need to synchronize their data with backend servers. Synchronization semantics have typically been set at the level of backend datastores. This is a major hindrance for enterprise applications that cannot assume a uniform storage model. In this paper, we present the SodaSync framework that provides a generic synchronization model for mobile enterprise applications that use heterogeneous backend stores. SodaSync exploits a unifying higher-level data model of service data objects (SDO) and introduces a persistence and synchronization framework for the model. It allows application programmers to express data and consistency requirements in terms of the SDO model and thereby emancipates them from the replication nuances of various backend stores. We present the major features of SodaSync, its architecture, and the status of our implementation.

Managed portal appliance: an experiment in extending the reach of Web applications

In the typical Web application, a client renders markup and the application or service is implemented as a set of tiered functions in the network. However, clients can contain resources useful for an application and network connections cannot always be assumed. In this paper, we consider extending the reach of a Web application to include: 1) access to and use of local client resources, and 2) operation while disconnected from the network. We, however, try to preserve desirable programming model and management characteristics of Web applications. We propose a system architecture and discuss an initial implementation using a portal as an example Web application.

Toward interoperable data synchronization with COSMOS

COSMOS (Co-Operative State Machines for Object Synchronization) is a method for specifying the behavior of a synchronizable data store by modeling the data store as a state machine. Such a model can be used to define a standard for interoperable data synchronization systems, defining the sequence of messages sent and received during synchronization without constraining the implementation of a conforming system. COSMOS models can be collected, studied and categorized, allowing a synchronization scheme with the properties appropriate for a given application to be selected from a catalog. Alternatively, for pre-existing synchronization systems built without a common standard, COSMOS models can serve as a specification for an adapter allowing the systems to interoperate.