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Smart IRIs


The SmartIri trait can be used to parse and validate IRIs, and in particular for converting Knora type IRIs between internal and external schemas. It validates each IRI it parses. To use it, import the following:

import org.knora.webapi.messages.SmartIri
import org.knora.webapi.messages.IriConversions._

Ensure that an implicit instance of StringFormatter is in scope:

import org.knora.webapi.messages.StringFormatter
implicit val stringFormatter: StringFormatter = StringFormatter.getGeneralInstance

Then, if you have a string representing an IRI, you can can convert it to a SmartIri like this:

val propertyIri: SmartIri = "".toSmartIri
If the IRI came from a request, use this method to throw a specific
exception if the IRI is invalid:

val propertyIri: SmartIri = propertyIriStr.toSmartIriWithErr(throw BadRequestException(s"Invalid property IRI: <$propertyIriStr>"))

You can then use methods such as SmartIri.isKnoraApiV2EntityIri and SmartIri.getProjectCode to obtain information about the IRI. To convert it to another schema, call SmartIri.toOntologySchema. Converting a non-Knora IRI returns the same IRI.

If the IRI represents a Knora internal value class such as knora-base:TextValue, converting it to the ApiV2Simple schema will return the corresponding simplified type, such as xsd:string. But this conversion is not performed in the other direction (external to internal), since this would require knowledge of the context in which the IRI is being used.

The performance penalty for using a SmartIri instead of a string is very small. Instances are automatically cached once they are constructed.

There is no advantage to using SmartIri for data IRIs, since they are not schema-specific (and are not cached). If a data IRI has been received from a client request, it is better just to validate it using StringFormatter.validateAndEscapeIri, and represent it as an org.knora.webapi.IRI (an alias for String).


The smart IRI implementation, SmartIriImpl, is nested in the StringFormatter class, because it uses Knora's hostname, which isn't available until the Akka ActorSystem has started. However, this means that the Scala type of a SmartIriImpl instance is dependent on the instance of StringFormatter that constructed it. Therefore, instances of SmartIriImpl created by different instances of StringFormatter can't be compared directly.

There are in fact two instances of StringFormatter:

  • one returned by StringFormatter.getGeneralInstance, which is available after Akka has started and has the API server's hostname (and can therefore provide SmartIri instances capable of parsing IRIs containing that hostname). This instance is used throughout the DSP-API server.
  • one returned by StringFormatter.getInstanceForConstantOntologies, which is available before Akka has started, and is used only by the hard-coded constant knora-api ontologies (see Generation of Ontologies in External Schemas).

This is the reason for the existence of the SmartIri trait, which is a top-level definition and has its own equals and hashCode methods. Instances of SmartIri can thus be compared (e.g. to use them as unique keys in collections), regardless of which instance of StringFormatter created them.

Last update: January 19, 2023