Friday, October 05, 2007

What the heck is SDI 1.0?

There's been alot of hype about "SDI 1.0" this year and some folks find it confusing - so here's a simple breakdown (mybe not perfect, but a start)...

The US government defines a Spatial Data Infrastructure, an "SDI", as the “consistent means to share geographic data among all users.” They go on to describe an SDI as the “technology, policies, criteria, standards and people necessary to promote geospatial information sharing throughout all levels of government, the private and non-profit sectors, and academia. It provides a base of practices and relationships among data producers and users that facilitates data sharing and use.”

The successful implementation of an SDI starts with the availability of content and services on the back-end and continues with front-end software clients for the end users. This type of a net-centric environment is dependent on industry-wide implementation of these open non-proprietary standards and specifications in software applications, often called standards-based commercial off-the-shelf software (SCOTS). A major push toward commercial embrace of SDIs is the endorsement of "SDI 1.0" by national geospatial organizations as part of the effort to coordinate geospatial standards and promote interoperability.

So given all that - here's is an initial crack at deciphering the bits and pieces of SDI 1.0...

- Web Features Service (WFS): The WFS implementation specification allows clients to retrieve and update geospatial data encoded in Geography Markup Language (GML) from multiple WFSs. It defines interfaces for data access and manipulation of geographic features and through these interfaces, a web user or service can combine, use, and manage geo-data. The basic Web Feature Service allows querying and retrieval of features. A transactional Web Feature Service (WFS-T) allows creation, deletion, and updating of features.

- Web Map Service (WMS): The WMS implementation specification supports the creation and display of registered and super-imposed maplike views (graphical images, such as GIF, JPEG, TIFF, and NITFS).

- Web Coverage Service (WCS): The WCS specification allows access to geospatial “coverages” (raster data sets) that represent values or properties of geographic locations rather than WMS-generated maps (pictures).

- Web Map Context (WMC): The WMC implementation specification is a companion to WMS. It describes how to save a map view comprised of many different layers from different Web Map Services.

- Geography Markup Language (GML): GML is eXtensible Markup Language (XML) encoding for the transport and storage of geographic information, including both the spatial and non-spatial properties of geographic features.

- Styled Layer Descriptor (SLD): The SLD standard defines the structure of an XML file that applies rendering or symbolization rules to features. An SLD requests a WMS to present a map according to submitted style rules.

- Catalog Services (CS-W): The CS-W provides an abstract model and protocol-specific solutions for the discovery of geospatial resources. Through catalog metadata and query interfaces, metadata properties are returned to the requestor, often embedded with links to actual data or services that allow the catalog to act as a referral service to other information resources.

- Filter Encoding Specification (FE): FE is used to express a query or filter using a predicate language, or terms and operators, stored in XML elements. FE is used in requests to WFS and queries to CS-W.


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