The Full Picture

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Components of GEOSS are expected to interoperate primarily
over network communication services by passing structured
messages. The GEOSS Plan speaks about defining both the struc-
ture of messages (syntax) and the meaning of data elements within
the message (semantics). With regard to syntax, the GEOSS Plan
states: “Systems interoperating in GEOSS agree to avoid non-stan-
dard data syntaxes in favour of well-known and precisely defined
syntaxes for data traversing system interfaces.” On semantics, the
GEOSS Plan states: “It is also important to register the semantics
of shared data elements so that any system designer can determine
in a precise way the exact meaning of data occurring at service
interfaces between components.”
In the wildland fire example, the standard for alert messages
provides an example of using standards for syntax and semantics.
Messages compliant with the alert standard are defined using both
of the most common international standard data syntaxes. Also,
the exact meanings of elements in those alert messages are defined
using the international standard for data semantics.
Another key standard referenced in the GEOSS Plan concerns
metadata. Metadata refers to descriptive information about the
data itself, which is essential for many aspects of data processing.
For instance, the GEOSS Plan calls out the standard for the syntax
and semantics of geospatial metadata. (The term ‘geospatial’
includes anything referenced to a place on the Earth.) Just as a
bibliographic catalogue entry specifies title, author, subject and
publication date, this standard specifies important characteristics
of geospatial data. Searchers use a few of these metadata elements
to discover data that may be of interest. Other metadata elements
are useful to evaluate what the data is about, and how it can be
applied effectively.
The standard service interface for network search adopted by
GEOSS is that used by libraries worldwide for searching online
catalogues. Consequently, GEOSS searching spans all manner of
resources, including geospatial metadata and alert messages,
books, scientific articles, museum collections, archives, and virtu-
ally any other information.
The standard search service defines how to specify searches
precisely. This includes latitude and longitude boundaries and
scientific terms, as well as bibliographic citations. The standard
can be used simply with Internet search engines, yet it has the
expressive power for complex data searches such as
chemical formulas and the pattern matching needed
for images.
Bringing it all together with GEOSS
Clearinghouse
GEOSS Clearinghouse acts as a cross-cutting catalogue
among registered resources, including services and
standards as well as data and information. GEOSS
Clearinghouse provides registry services with a
description of each of the formally contributed compo-
nents of GEOSS; metadata about the various data and
information holdings in each of the contributed
components; technical specifications for using the
services exposed by the contributed components, and
descriptions of key interoperability standards in use
across the contributed components of GEOSS.
The GEOSS Plan states: “GEO Members and
Participating Organizations and their contributions
will be catalogued in a publicly accessible, network-
distributed clearinghouse maintained collectively
under GEOSS. The catalogue will itself be subject to
GEOSS interoperability specifications, including the
standard search service and geospatial services.”
Service interfaces to GEOSS Clearinghouse help users
discover, evaluate and use data and information resource
across all GEOSS components. For instance, the Global
Spatial Data Infrastructure (GSDI) is a GEO Participating
Organization and a partnership among 60 nations and
organizations in its own right. Dedicated to sharing
geospatial data, its GSDI Registry provides interoperable
access to the holdings compiled through over 400 cata-
logue servers. The GSDI Registry is a contributed GEOSS
Component and already complies with the standard search
service interface and geospatial services given in the
GEOSS Plan. This means that users of GEOSS
Clearinghouse can already discover hundreds of thousands
of geospatial data items across the interoperable catalogues
registered by GSDI.
Of course, searchers for Earth observations data and
services need to find more than just those resources
and services specifically registered in GEOSS. Because
GEOSS has adopted existing standards already in
broad use, GEOSS Clearinghouse searchers can also
discover, evaluate and use the broadest range of useful
information – millions of items across many thou-
sands of libraries worldwide, as well as Web pages and
‘deep Web’ databases.
GEOSS is meeting the challenge to realize a system of
comprehensive, coordinated, and sustained Earth observa-
tion. Mindful of the wide diversity and independence of its
component systems, the GEOSS Architecture embodies
principles that enhance interoperability. With particular
attention to international standards and common interop-
erability arrangements, the GEOSS Architecture and GEOSS
Clearinghouse are enabling GEO Members and
Participating Organizations to cooperate in realizing GEOSS.
The resulting system of systems is simplifying access to all
manner of relevant resources for all users worldwide.
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Search service
An example of a search service message, using the international standard
adopted by GEOSS.
version=1.1&maximumRecords=100&recordSchema=XML&
query=(geo.bounds within/partial/nwse “43.8 –101.48 31.8 –77.8”)
and(geo.keywords any “biologic ecologic”)
terms, etc
latitude,
longitude
boundaries
Source: Eliot Christian
GEOSS C OMPONENTS – OBSERVING S YSTEMS