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ImplementationHELIO is being implemented with a service-oriented architecture – this basically means that capabilities that are required are split into a number of separate services. In principle, the services can be grouped into two areas: search for interesting events and phenomena; and identify, locate and retrieve observations.The first of these is quite difficult to quantify – what information is required and how it will be used depends on the science problem being addressed. HELIO is therefore creating a set of services that we believe will provide the types of capability that might be needed; these can be combined together using the workflow tool deployed by HELIO – Taverna. The Heliophysics Event Catalogue and Heliophysics Feature Catalogue facilitate searches on events and features throughout the heliosphere and contain that have been recognized by semi-automated techniques. Because some occurrences are quite subtle and cannot easily be detected, the Metadata Evaluation Service allows the user to manipulate time series data and search for events; a similar capability will be provided for image data. In order to understand the temporal and spatial relationship between phenomena and events observed in different parts of the Solar System, the ability to run models is provided; this is just one of a number of processing capabilities that can be provided. Quick-look information, combining inputs from several sources, will be generated by the Context Service and present them as a means of helping the user to decide which events are most interesting and worth pursuing. In comparison to looking for interesting events, once the times, locations and types of observation required have been determined the task of matching these to data is relatively straightforward. The Instrument Capabilities Service and Instrument Location Service, together with Observation Coverage Service allow the user needs know whether suitable observations were made at the required location at the desired time. The Data Provider Access Service is then used to find the required data, wherever and however they are stored and accessed in archive around the world. Of course, the split between the tasks is not rigid. As part of the task of determining whether it is worth pursuing a particular event, a user is interested in the quality of observations available. Also, a user may have already made certain decisions about what they need based on other criteria; the design of HELIO allows them to use services and they jump into workflows at any point. A Semantic Mapping Service is used to manage differences in the ways that the communities describe their data. Storage and Processing services are also available; authorization to use these services is managed by another service. All services are described in a the HELIO Registry Service.
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