Construct
An Open Source Pervasive Systems Platform

Simon Dobson, Paddy Nixon, Lorcan Coyle, Steve Neely, Greame Stevenson and Graham Williamson
Systems Research Group
Adaptive Information Cluster
UCD School of COmputer Science and Informatics
UCD Belfield, Dublin, Ireland
Firstname.Lastname@ucd.ie




Construct differs from other pervasive systems platforms
in a number of key respects. It is completely standards-
based, using RDF as its data exchange model and
ZeroConf for resource discovery. It supports a knowledge-
centric model of interaction where clients' actions are
driven by queries and triggers about the context of the
system. It uses gossiping to maintain a consistent state
across a distributed data structure, which maximises
robustness and scalability and avoids many problems with
hot-spots and hot-paths in communications. Finally, it
treats all information sources uniformly as sensors acting
as inputs to uncertain reasoning algorithms.
Keywords-component; autonomic, pervasive, context aware,
middleware.
I. INTRODUCTION
Pervasive and autonomic systems share many features in
common: they are highly adaptive, involve a large and
dynamically-changing population of components and services,
must deal with a variety of sensors and information sources
delivering partial and uncertain results and must deliver an
overall experience which is simultaneously adaptive to
changing context but stable enough to present a predictable
and scrutable service to users and other systems. Building
systems which meet these criteria is challenging, involves
considerable infrastructural development work, and requires
the designer to understand a wide range of quite subtle issues -
- all of which interfere with the development of application-
level services.

It is attractive to address as many of the infrastructural issues
as possible using middleware, providing a common platform
on which to construct more advanced applications and
services. A number of such platforms heve been developed:
the Context Toolkit, Project Aura, Cooltown, Semantic Space
and others. Each has been highly influential, but also presents
challenges (of maintenance, openness, availability, scalability
or abstraction) for new projects. We have designed Construct
to address these issues. The goals of Construct are:

• to provide an open, standards-based platform to
encourage and facilitate the development of pervasive
and autonomic systems;
• to simplify the development of novel systems by
providing a collection of pre-built sensors, modules
and services addressing important system features;
• to act as a target for research into adaptive systems
design, and into programming language constructs for
such systems; and
• to nurture a community of developers who can build
on each others' work.
Construct differs from other pervasive systems platforms in a
number of key respects. It is completely standards-based,
using RDF as its data exchange model and ZeroConf for
resource discovery. It supports a knowledge-centric model of
interaction where clients' actions are driven by queries and
triggers about the context of the system. It uses gossiping to
maintain a consistent state across a distributed data structure,
which maximises robustness and scalability and avoids many
problems with hot-spots and hot-paths in communications.
Finally, it treats all information sources uniformly as sensors
acting as inputs to uncertain reasoning algorithms.

II. FUNDAMENTALS

The majority of the codebase is written in Java. At the heart of
the infrastructure is a component loader which instantiates the
five core services at runtime. As new peers come online they
discover other nodes using an implementation of the zeroconf
protocol [7]. When entities start-up they also use zeroconf to
locate instances of Construct. The result of this is a reference
to the discovery service that supplies the manifests for
additional local services. Manifests are described using the
Web Service Definition Language (WSDL), which provides
information on how to connect to and use each service. All
data in Construct are modelled using the Resource Description
Framework (RDF). RDF is an open-standard that meets our
requirement of providing a common language with which to
represent information generated within a networked home.
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