The OGC Catalogue services support the ability to publish and search collections
of descriptive information (metadata) for data, services, and related information
objects (Douglas et al. 2007). The metadata in catalogues represent resource characteristics that can be queried and presented for evaluation and further processing by
both humans and software. For example, once the metadata information about each
farm is maintained in a catalogue service, searching for farms of interest based on
location, opening dates, products, and crops in different seasons would be a very
straightforward approach, as defined in the catalogue service standard. To reach this
goal, the OGC Catalogue service standard defines the way to organize the metadata
information, to define query against the metadata in the request, and to present the
matched results in the response.
The OGC Web Map Service (WMS) is mainly for producing maps of spatially
referenced data dynamically from geographic information (de la Jeff 2006). In
particular, it defines a “map” to be a portrayal of geographic information as a digital
image file suitable for display on a computer screen. The WMS-produced maps are
generally rendered in a pictorial format such as PNG, GIF, or JPEG or occasionally
as vector-based graphical elements in Scalable Vector Graphics (SVG) or Web
Computer Graphics Metafile (WebCGM) formats. In this standard, what needs to
be rendered (such as specific data layer) and how are clearly defined.
The OGC Web Feature Service (WFS) standard specifies the behavior of a service
that provides transactions on and access to geographic features (Panagiotis 2010). It
mainly specifies discovery operations, query operations, locking operations, and
transaction operations. The WFS actually represents a change in the way the
geographic information is created, modified, and exchanged on the Internet. Rather
than sharing geographic information at the file level using File Transfer Protocol
(FTP), for example, the WFS offers direct fine-grained access to the geographic
information at the feature and feature property level. The Web Feature Services
allow clients to only retrieve or modify the data they are seeking, rather than
retrieving a file that contains the data they are seeking and possibly much more.
That data can then be used for a wide variety of purposes, including purposes other
than their producers’ intended ones. For example, once the national farm geolocation
data is exposed as a Web Feature Service, any small part of it, such as all the farms
located in one specific state, county, or city or even in a user-specified area, could be
dynamically exported. One of the significant benefits of this service is that the data
owner only needs to maintain one copy of this national-scale data, and the WFS
enables the flexibility of accessing to any subset of this agricultural data.
The OGC Web Coverage Service (WCS) standard supports the electronic
retrieval of geospatial data as “coverages” – that is, digital geospatial information
representing spaceÀ/time-varying phenomena (Peter 2010). Unlike the WMS,
which portrays spatial data to return static maps (rendered as pictures by the
server), the WCS provides available data together with their detailed descriptions
which may be interpreted, extrapolated, etc., and not just portrayed. Unlike the
WFS, which returns discrete geospatial features, WCS returns coverages
representing spaceÀ/time-varying phenomena that relate a spatiotemporal domain
to a (possibly multidimensional) range of properties. One use case of utilizing the
5 Standards and Interoperability
77
of descriptive information (metadata) for data, services, and related information
objects (Douglas et al. 2007). The metadata in catalogues represent resource characteristics that can be queried and presented for evaluation and further processing by
both humans and software. For example, once the metadata information about each
farm is maintained in a catalogue service, searching for farms of interest based on
location, opening dates, products, and crops in different seasons would be a very
straightforward approach, as defined in the catalogue service standard. To reach this
goal, the OGC Catalogue service standard defines the way to organize the metadata
information, to define query against the metadata in the request, and to present the
matched results in the response.
The OGC Web Map Service (WMS) is mainly for producing maps of spatially
referenced data dynamically from geographic information (de la Jeff 2006). In
particular, it defines a “map” to be a portrayal of geographic information as a digital
image file suitable for display on a computer screen. The WMS-produced maps are
generally rendered in a pictorial format such as PNG, GIF, or JPEG or occasionally
as vector-based graphical elements in Scalable Vector Graphics (SVG) or Web
Computer Graphics Metafile (WebCGM) formats. In this standard, what needs to
be rendered (such as specific data layer) and how are clearly defined.
The OGC Web Feature Service (WFS) standard specifies the behavior of a service
that provides transactions on and access to geographic features (Panagiotis 2010). It
mainly specifies discovery operations, query operations, locking operations, and
transaction operations. The WFS actually represents a change in the way the
geographic information is created, modified, and exchanged on the Internet. Rather
than sharing geographic information at the file level using File Transfer Protocol
(FTP), for example, the WFS offers direct fine-grained access to the geographic
information at the feature and feature property level. The Web Feature Services
allow clients to only retrieve or modify the data they are seeking, rather than
retrieving a file that contains the data they are seeking and possibly much more.
That data can then be used for a wide variety of purposes, including purposes other
than their producers’ intended ones. For example, once the national farm geolocation
data is exposed as a Web Feature Service, any small part of it, such as all the farms
located in one specific state, county, or city or even in a user-specified area, could be
dynamically exported. One of the significant benefits of this service is that the data
owner only needs to maintain one copy of this national-scale data, and the WFS
enables the flexibility of accessing to any subset of this agricultural data.
The OGC Web Coverage Service (WCS) standard supports the electronic
retrieval of geospatial data as “coverages” – that is, digital geospatial information
representing spaceÀ/time-varying phenomena (Peter 2010). Unlike the WMS,
which portrays spatial data to return static maps (rendered as pictures by the
server), the WCS provides available data together with their detailed descriptions
which may be interpreted, extrapolated, etc., and not just portrayed. Unlike the
WFS, which returns discrete geospatial features, WCS returns coverages
representing spaceÀ/time-varying phenomena that relate a spatiotemporal domain
to a (possibly multidimensional) range of properties. One use case of utilizing the
5 Standards and Interoperability
77