Use ows4R with OGC CSW (Catalogue Service for the Web)

This vignette shows how to use ows4R with a Catalogue Service for the Web (OGC CSW).

An overview of the Catalogue Service (CSW) can be found on the official OGC webpage: https://www.ogc.org/standard/cat/

Create CSW Client

In order to operate on a Catalogue Service, you need to create an interface in R to this CSW. This is done with the class CSWClient, as follows:

CSW <- CSWClient$new("http://localhost:8080/csw", "2.0.2", logger = "INFO")

You can define the level of logger: “INFO” to get ows4R logs, “DEBUG” for all internal logs (such as as Curl details). It is also possible to define a username and credentials in case operations would require an authentication to use the Catalogue Service.

For operations that require authentication (e.g. CSW Transaction operations on GeoNetwork), you may need to specify the user and pwd parameters.

Get Capabilities (GetCapabilities)

When create the CSWClient, ows4R will run a GetCapabilities request. To access the CSW Capabilities and its sections, you can use the following code:

caps <- CSW$getCapabilities()

Describe a record (DescribeRecord)

NOT YET SUPPORTED

Get a record (GetRecordById)

The below example shows how to get a metadata record by ID, and bind it with geometa ISO/OGC metadata classes.

#supposing a metadata identified as "my-metadata-identifier"
md <- CSW$getRecordById("my-metadata-identifier", outputSchema = "http://www.isotc211.org/2005/gmd")

Get records (GetRecords)

This section gives several examples how to get records with the ows4R CSW client.

Basic query

A basic GetRecords request can be done with the following code:

records <- CSW$getRecords()

By default, this request will return the 5 first metadata records. These records are returned in the Dublin Core metadata format, handled as list in R.

Query with maxRecords parameter

To change the maximum number of records to be returned, use the maxRecords parameter

records <- CSW$getRecords(maxRecords = 20L)

Query with CQL filters

To query records based on a filter, we introduce 2 notions inherited from the CSW specification: a query handled in ows4R that will accept as parameter a constraint (corresponding to a given filter).

Query with CQL Filter on metadata title

The example below shows you:

  • how to create a CSWConstraint specifying a CQL text filter on metadata title. Here the properties refer to the Dublin Core metadata format, hence the notation dc:title.
  • how to set a CSWQuery based on this constraint/filter
  • how to get get metadata records based on the query
cons <- CSWConstraint$new(cqlText = "dc:title like '%ips%'")
query <- CSWQuery$new(constraint = cons)
records <- CSW$getRecords(query = query)

Query with CQL Filter on metadata title and abstract

Another example of GetRecords query with a CQL filter based on two properties (title, abstract):

cons <- CSWConstraint$new(cqlText = "dc:title like '%ips%' and dct:abstract like '%pharetra%'")
query <- CSWQuery$new(constraint = cons)
records <- CSW$getRecords(query = query)

Query with CQL Filter on metadata identifier

We may also try to perform a ``GetRecords``` based on a metadata identifier. In case there is an existing metadata record with such identifier, we expect to get a list of length 1.

cons <- CSWConstraint$new(cqlText = "dc:identifier = 'my-metadata-identifier'")
query <- CSWQuery$new(constraint = cons)
records <- CSW$getRecords(query = query)

Query with OGC filters

Instead of using a CQL text filter, ows4R allows to specify an OGC Filter as basis to build the CSWConstraint. OGC Filters can be created with the class/function OGCFilter specifying an expression, among the following:

  • Simple OGC expressions
    • PropertyIsEqualTo / PropertyIsNotEqualTo
    • PropertyIsLessThan / PropertyIsGreaterThan
    • PropertyIsLessThanOrEqualTo / PropertyIsGreaterThanOrEqualTo
    • PropertyIsLike
    • PropertyIsNull
    • PropertyIsBetween
    • BBOX
  • Combinations of OGC expressions
    • And
    • Or
    • Not

Query with OGC filter - PropertyIsLike

The below example constructs a constraint with an OGCFilter made of a PropertyIsLike predicate on CSW AnyText. The result will be a list of records for which _any text is like ‘%Physio%’ (all records for which the string ‘Physio’ is included):

filter <- OGCFilter$new( PropertyIsLike$new("csw:AnyText", "%Physio%"))
cons <- CSWConstraint$new(filter = filter)
query <- CSWQuery$new(constraint = cons)
records <- csw2$getRecords(query = query)

Query with OGC filter - PropertyIsEqualTo

filter <- OGCFilter$new( PropertyIsEqualTo$new("csw:AnyText", "species"))
cons <- CSWConstraint$new(filter = filter)
query <- CSWQuery$new(constraint = cons)
records <- CSW$getRecords(query = query)

Transaction - Insert,Update,Delete (Transaction)

If the CSW server used supports Transaction operations (Insert, Update, Delete), ows4R allows you to perform these operations. The following examples highlight the different operations available:

Insert

mdfile <- system.file("extdata/data", "metadata.xml", package = "ows4R")
md <- geometa::ISOMetadata$new(xml = XML::xmlParse(mdfile))
insert <- CSW$insertRecord(record = md)
insert$getResult() #TRUE if inserted, FALSE otherwise

Update (Full)

md$identificationInfo[[1]]$citation$setTitle("a new title")
update <- CSW$updateRecord(record = md)
update$getResult() #TRUE if updated, FALSE otherwise

Update (Partial)

recordProperty <- CSWRecordProperty$new("apiso:Title", "NEW_TITLE")
filter = OGCFilter$new(PropertyIsEqualTo$new("apiso:Identifier", md$fileIdentifier))
constraint <- CSWConstraint$new(filter = filter)
update <- CSW$updateRecord(recordProperty = recordProperty, constraint = constraint)
update$getResult() #TRUE if updated, FALSE otherwise

Delete

delete <- CSW$deleteRecordById(md$fileIdentifier)
delete$getResult() #TRUE if deleted, FALSE otherwise

The methods insertRecord and updateRecord also support options to deal with geometa ISOMetadata objects. The option geometa_validate is set by default to TRUE and operates a validation vs. ISO/TC 19139 schemas. The option geometa_inspire can be enabled to test the metadata with INSPIRE. Records inserted/updated through CSW-T will then include a footer of XML comments containing the validation details. See the geometa documentation