Chapter 20. OGSA-DAI case study - SEE-GEO
The SEE-GEO (SEcurE access to GEOspatial services) project
used many of the features of OGSA-DAI when developing a service to
provide access to geo-spatial information on a grid.
As part of a geo-linking interoperability experiment, the project
addressed a scenario which involved accessing and joining data from
two existing data resources and then rendering this data in a
graphical format. The two data resources are as follows:
Census statistics: this contains attributes about a region, e.g. the
cost of a loaf of bread, and is accessed via a Geo-data access service
Borders data: this is data on unique geographical regions encoded as
polygons and is accessed via a web feature service (WFS).
By joining data from these data resources questions such as: "how does
the cost of a loaf of bread vary across different regions in Scotland?",
can be answered.
The project used OGSA-DAI to develop a geo-linking service which would
get data from each of the two data resources and execute a join
across these. It would then use the joined data, in conjunction with a
feature portrayal service (FPS), to get an image representation of the
joined data which could then be returned to the client.
Figure 20.1. SEE-GEO geo-linking service constructed using OGSA-DAI
The solution uses a number of features of OGSA-DAI:
OGSA-DAI's data resource extensibility points are used to enable the
GDAS (and so the census data) and the WFS (and so the borders data) to
be accessed within OGSA-DAI workflows.
OGSA-DAI's support for application-specific activities allowed
application-specific activities for querying the above data resources
as well as executing the join across the data resources and also the
conversion of the joined data to an image via the FPS to be developed
OGSA-DAI's support for different types of delivery mechanism allowed
the image to be delivered via FTP rather than via the more inefficient
SOAP over HTTP.
OGSA-DAI gave SEE-GEO many advantages including:
The leveraging of OGSA-DAI's workflow execution functionality and
out-of-the-box activities for data delivery and interacting with other
grid technologies (e.g. GridFTP).
The ability to enforce additional levels of security.
To utilise other grid technologies via OGSA-DAI.
A toolkit to develop application-specific activities and
support for application-specific data resources
A framework that allowed them to choose data resources dynamically
with very little effort.