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use of workflows to the community. Second, and more importantly, it left a set of
web services to query online databases. The VSO (2014) is a search engine for
heliophysical data from both ground- and space-based observatories. VSO allows
the user to search these data centres (and many others) for data in a speci
c time
range and for speci
c instruments. Finally, AMDA (2014) is a GUI that allows for
searching, downloading, processing, and plotting of heliophysical data.
HELIOGate builds on top of these projects by offering a tool capable of com-
bining and orchestrating existing web services in a flexible and easily con
gurable
fashion. HELIOGate acknowledges different users
preferences by allowing them to
integrate workflows in their language of preference. Finally, HELIOGate connects
to sizeable computation and storage infrastructures to execute data processing
codes.
Scienti
'
c investigation in heliophysics comprises a large variety of use cases that
may be useful only for the investigation of a speci
c event; this characteristic of
the discipline stresses the necessity of reusability whenever it is possible. In the
development of HELIOGate, we aim at maximizing reusability in both the main
fields tackled by the portal: propagation models and data processing. In propagation
models, we have developed a three-layer approach in the development of work-
flows that ensures that the basic components can be reused as much as it is possible.
At the lowest layer, there are sets of simple workflows that implement use cases,
that is, descriptions of atomic operations that can be used across different scientific
investigations. A very common example of a use case and its workflow imple-
mentation for heliophysics is the invocation of a HELIO service (a remote web
service) to query a catalogue of events. An atomic workflow that connects to a web
service and retrieves information can be reused in all the propagation models that
need information from that service. Atomic workflows are then combined in
metaworkflows: more complex entities that are designed to solve science cases
(the description of scienti
c challenges). Science cases can be extended to cover the
investigation of a set of events rather than a single one; in this case, we extend the
meta-workflows with the parameter sweep execution capacities of WS-PGRADE.
The technology offered by gUSE and WS-PGRADE provided a natural and
powerful solution to all the needs of the community and thus shaped the main
characteristics of the HELIO portal as a
gurable
propagation modelling and data processing support. For the users who want to use
existing TAVERNA (2014) workflows or develop new solutions with different
platforms, HELIOGate uses the workflow interoperability technology offered by
SHIWA (2014) to offer the capability of integrating their own solutions.
“
workflow-oriented
”
tool for con
14.3 Propagation Models
To investigate the relation between the Sun and the other bodies of the Solar
System, heliophysicsts use propagation models that describe and predict the
movement of physical events through the Solar System. The HELIO project
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