Catalog Service for the Web
'Catalog Service for the Web' (CSW or sometimes seen as Catalog Service - Web) is a standard for exposing a catalogue of geospatial records on the Internet (over HTTP).
CSW is one part (or "profile") of the OGC Catalog Service, which defines common interfaces to discover, browse, and query metadata about data, services, and other potential resources.
The catalogue is made up of metadata records that describe these types of data:
- geospatial data (e.g. KML)
- geospatial services (e.g. WMS)
- other related resources
The format of each metadata record is defined in the standard only as XML, but is typically an encoding of Dublin Core, ISO19139 or FGDC metadata and with UTF8 character encoding. Whatever format is used, each record must contain a set of core fields, such as: Title, Format, Type (e.g. Dataset, DatasetCollection or Service), BoundingBox (a rectangle of interest, expressed in latitude and longitude), Coordinate Reference System and Association (a link to another metadata record).
- GetCapabilities - returns the properties of requests that are accepted by the server
- DescribeRecord - returns info about the model of records
- GetDomain (optional) - returns for a given record field, the range of values held by records
- GetRecords - search for records, returning record IDs
- GetRecordsById - returns records, specified by their ID
- Harvest (optional) - create/update metadata by asking the server to 'pull' metadata from somewhere
- Transaction (optional) - create/edit metadata by 'pushing' the metadata to the server
Requests can encode the parameters in three different ways:
- GET with URL parameters
- POST with form-encoded payload
- POST with XML payload
Responses are in XML.
Versions 2.0.0, 2.0.1 and 2.0.2 are subtly different, and different vendors implement them with variations. Typically a CSW server will accept requests in one CSW version only, and it is up to the client to be flexible. e.g. ESRI Geoportal can be configured to harvest documents from CSW servers of a variety of versions and vendor variants  such as "GeoNetwork CSW 2.0.2 APISO".
- Web Map Service (WMS)
- Web Feature Service (WFS)
- Web Coverage Service (WCS)
- Web Processing Service (WPS)
- OGC Catalogue Service
- OpenGIS Catalogue Service Implementation Specification (PDF)
- Commercial implementations of CSW 2.0.2
- pycsw - Open source Python implementation of CSW
- GeoNetwork - Open source Java implentation of CSW
- Open source Python client for CSW 2.0.2
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