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The Semantic Grid Pervasive Computing |
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The Semantic Grid Pervasive Computing |
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Pervasive Computing is the means by which the digital world of the Grid couples into our physical world. I argue for combined work on grid and pervasive computing, and for a semantic approach.
Pervasive or ubiquitous computing is about devices everywhere; e.g. in everyday artefacts, in our clothes and surroundings, in the external environment. The term ubiquitous was adopted by Xerox through the work of Mark Weiser, who emphasised the 'calm' aspects, i.e. the computing is very much in the background. In Europe it's part of the Ambient Intelligence vision.
Some of our grid applications involve pervasive computing, including the coupling of sensors to the grid (such as in a 'smart laboratory'), collaboration technologies, and signal processing based on data from medical devices. So the Grid doesn't necessarily present itself as a socket on the wall (like the electricity utility after which it is named) - it has a more pervasive coupling with the physical world.
Conversely, some of our pervasive applications need the Grid in the background. As sensors and sensor arrays evolve, we can acquire data with higher temporal or spatial resolution, and this increasing bulk of (often realtime) data demands the computational power of the Grid. Meanwhile many pervasive projects are currently small scale, due to small numbers of devices or small numbers of users, but will demand more grid processing as numbers scale up.
Both are about large numbers of distributed processing elements. At an appropriate layer of abstraction, i.e. from a few thousand feet, both grid and pervasive computing involve similar computer science challenges in distributed systems. These include service description, discovery and composition, issues of availability and mobility of resources, and of course security, authentication and trust. Both rely on interoperability to achieve their goals. And the peer-to-peer paradigm is relevant across the picture.
This abstracted view blurs the boundary between the Grid and the devices. For example, we can ask to what extent we can push the computation from the Grid back towards the devices? And to what extent can we achieve commonality in the middleware; e.g. how far can the OGSA infrastructure be applied towards the devices side of the picture? We envisage grid services relating to the sensors, be they polution monitors, physiological signals, motion or location information.
There is a fundamental trade-off that is being explored here. On the one hand the computational power and storage capability of our devices increases as the technology improves. But at the same time we move into a world in which our devices can delegate storage and computation to the Grid, perhaps in real-time through greater connectivity and devices which are increasingly 'always on'. There's no one correct answer - the best solution for a given application can be clear and in general we do need to explore both routes.
Perhaps most profoundly, Grid computing and pervasive computing are two visions of the future that really do seem to be upon us, and so surely they must be investigated together rather than in isolation.
Then of course there is the third vision: the Semantic Web. This gives us the three corners of "Dave's Triangle" as depicted below. Above I argued the bottom edge of the triangle.
In the Semantic Grid we argue for the application of Semantic Web technologies to grid infrastructure and applications - the right hand edge of the triangle. We can also argue the left hand edge - that the full richness of the pervasive vision also needs the Semantic Web technologies. Again it's all about semantic interoperability. A key motivation for the semantic interop on the Grid is the need to assemble new Grid applications with ease (and preferably automatically), and surely we wish to do this with pervasive applications too. Essentially we have lots of distributed bits and pieces that need to work together, and we'd like this to happen without manual intervention - our autonomous software agents can do it (and things can be autonomic and one day can self-organise).
Again we need service description, discovery and composition, and indeed research areas such as Semantic Web Services are being applied both to Grid and to Pervasive computing. However, semantic interoperability applies to content as well as services and there is strong evidence that pervasive computing research and development projects do not always address these information and knowledge issues (just look in the proceedings of a pervasive computing conference). In fact I feel they pay less attention to such issues than Grid projects, which more often are motivated by information requirements.
The picture is improving with standards for representing e.g. sensor data, but we need the metadata too - for example, we need to achieve semantic annotation with context information at source. So metadata schema need to be established. To enjoy the magic of the Semantic Web we also need a means of creating and sharing URIs to get the added value of linking up disparate metadata via the objects it describes. Interestingly there's a whole new way of tying 'stuff' together here in the pervasive world because physical object and physical space provide more ways of tying that metadata together. There are great opportunities here.
As with Semantic Grid we will certainly find that we are pushing the Semantic Web technologies quite hard. For example, current solutions (such as triple stores) tend to favour a world of fairly static metadata - grid applications challenge this, and pervasive more so. So there's much important work to be done on this edge of the triangle.
And so to all three - the full richness of the grid, pervasive and semantic visions. There are people who will argue that each of these futures will surely happen, and I've argued that there are clear reasons why they need to happen together. Hence it is clear to me that we need to be exploring that combined world - the whole triangle! Through combining grid and pervasive and semantic we see a comprehensive infrastructure for the vision of 'ambient intelligence'. It is the manifestation of the Semantic Grid in the physical world.
Exploring these three visions together requires working across at least three communities. With Semantic Grid we bridge the Web and Grid communities, for the "Semantic Pervasive Grid" we touch the devices and the next generation of the pervasive networking infrastructure too.
A number of projects are driving this forward, including the UK e-Science projects connected with the Equator project and some under the Ambient Intelligence banner. As with Semantic Grid, we also need to put in place the community mechanisms to enable this all to happen. Organisations such as the Global Grid Forum provide the necessary environment for agreement about those schemes that will provide interop. How do we do that for semantic pervasive computing?
I have argued a case here based on engineering - to build the systems we need to build, these are the technologies we need. The sad thing is that the measure of success of the semantic grid, and of ubiquitous computing, and of semantic pervasive etc, is that we've succeeded when nobody knows it's there!
The real motivation for grid computing is the new science we can do with the power of our computers. That's why we want to build the grid applications in the first place. So remember also the power of pervasive computing - such as new ways to augment our experience and improve our quality of life (and of course to assist those scientific discoveries). Those increasingly powerful devices coupled to the increasingly powerful grid fabric are increasingly capable of knowledge processing. Think about that world of knowledgeable devices.
And let's challenge that "disappearing computer" and the aspiration to "seamlessness". Let's use these technologies to do new and interesting and creative and fun things. Let's have something appearing to replace the disappearing computer - let's have some new seams!
David De Roure, Madrid, May 2003
Web page maintained by David De Roure,
dder@ecs.soton.ac.uk