Package org.dspace.content.crosswalk

Class QDCCrosswalk

  • All Implemented Interfaces:
    DisseminationCrosswalk, IngestionCrosswalk, NameAwarePlugin
    public class QDCCrosswalk
extends SelfNamedPlugin
implements DisseminationCrosswalk, IngestionCrosswalk
    Configurable QDC Crosswalk

    This class supports multiple dissemination crosswalks from DSpace internal data to the Qualified Dublin Core XML format (see http://dublincore.org/).

    It registers multiple Plugin names, which it reads from the DSpace configuration as follows:

    Configuration

    Every key starting with "crosswalk.qdc.properties." describes a QDC crosswalk. Everything after the last period is the plugin instance, and the value is the pathname (relative to dspace.dir/config) of the crosswalk configuration file.

    You can have two aliases point to the same crosswalk, just add two configuration entries with the same value, e.g. 

        crosswalk.qdc.properties.QDC = xwalk/qdc.properties
    crosswalk.qdc.properties.default = xwalk/qdc.properties
    The first line creates a plugin with the name "QDC" which is configured from the file dspace-dir/xwalk/qdc.properties.

    Since there is significant overhead in reading the properties file to configure the crosswalk, and a crosswalk instance may be used any number of times, we recommend caching one instance of the crosswalk for each alias and simply reusing those instances. The PluginService does this by default.

    Each named crosswalk has two other types of configuration lines:

    XML Namespaces: all XML namespace prefixes used in the XML fragments below must be defined in the configuration as follows. Add a line of the form: 

      crosswalk.qdc.namespace.{NAME}.{prefix} = {namespace-URI}
    e.g. for the namespaces dc and dcterms in the plugin named QDC, add these lines: 
    crosswalk.qdc.namespace.QDC.dc = http://purl.org/dc/elements/1.1/
 crosswalk.qdc.namespace.QDC.dcterms = http://purl.org/dc/terms/

    Finally, you need to declare an XML Schema URI for the plugin, with a line of the form 

      crosswalk.qdc.schema.{NAME} = {schema-URI}
    for example, 
    crosswalk.qdc.schemaLocation.QDC  = \
  http://purl.org/dc/terms/ \
  http://dublincore.org/schemas/xmls/qdc/2003/04/02/qualifieddc.xsd
    Author:
    Larry Stone

    • Constructor Detail

      • QDCCrosswalk

        public QDCCrosswalk()

    • Method Detail

      • initStatic

        public static void initStatic()
        Call this method again in tests to repeat initialization if necessary.

      • getPluginNames

        public static String[] getPluginNames()

      • getNamespaces

        public org.jdom2.Namespace[] getNamespaces()
        Description copied from interface: DisseminationCrosswalk
        Get XML namespaces of the elements this crosswalk may return. Returns the XML namespaces (as JDOM objects) of the root element.
        Specified by:
        getNamespaces in interface DisseminationCrosswalk
        Returns:
        array of namespaces, which may be empty.

      • getSchemaLocation

        public String getSchemaLocation()
        Description copied from interface: DisseminationCrosswalk
        Get the XML Schema location(s) of the target metadata format. Returns the string value of the xsi:schemaLocation attribute that should be applied to the generated XML.

        It may return the empty string if no schema is known, but crosswalk authors are strongly encouraged to implement this call so their output XML can be validated correctly.

        Specified by:
        getSchemaLocation in interface DisseminationCrosswalk
        Returns:
        SchemaLocation string, including URI namespace, followed by whitespace and URI of XML schema document, or empty string if unknown.

      • canDisseminate

        public boolean canDisseminate​(DSpaceObject dso)
        Description copied from interface: DisseminationCrosswalk
        Predicate: Can this disseminator crosswalk the given object. Needed by OAI-PMH server implementation.
        Specified by:
        canDisseminate in interface DisseminationCrosswalk
        Parameters:
        dso - dspace object, e.g. an Item.
        Returns:
        true when disseminator is capable of producing metadata.

      • ingest

        public void ingest​(Context context,
                   DSpaceObject dso,
                   List<org.jdom2.Element> ml,
                   boolean createMissingMetadataFields)
            throws CrosswalkException,
                   IOException,
                   SQLException,
                   AuthorizeException
        Description copied from interface: IngestionCrosswalk
        Crosswalk metadata from external XML representation to DSpace internal representations. This version accepts metadata as a List of JDOM XML elements. It interprets the contents of each element and adds the appropriate values to the DSpace Object's internal metadata represenation.

        Note that this method may be called several times for the same target Item, if the metadata comes as several lists of elements, so it should not add fixed metadata values on each or they may appear multiples times.

        NOTE:
        Most XML metadata standards (e.g. MODS) are defined as a "root" element which contains a sequence of "fields" that have the descriptive information. Some metadata containers have a "disembodied" list of fields, rather than the root element, so this ingest method is intended to accept that bare list of fields. However, it must also accept a list containing only the "root" element for the metadata structure (e.g. the "mods:mods" wrapper in a MODS expression) as a member of the list. It can handle this case by calling the single-element version of ingest() on the "root" element.

        Some callers of the crosswalk plugin may not be careful about (or capable of) choosing whether the list or element version should be called.

        Specified by:
        ingest in interface IngestionCrosswalk
        Parameters:
        context - DSpace context.
        dso - DSpace Object (Item, Bitstream, etc) to which new metadata gets attached.
        ml - List of XML Elements of metadata
        createMissingMetadataFields - whether to create missing fields
        Throws:
        CrosswalkInternalException - (CrosswalkException) failure of the crosswalk itself.
        CrosswalkObjectNotSupported - (CrosswalkException) Cannot crosswalk into this kind of DSpace object.
        MetadataValidationException - (CrosswalkException) metadata format was not acceptable or missing required elements.
        IOException - I/O failure in services this calls
        SQLException - Database failure in services this calls
        AuthorizeException - current user not authorized for this operation.
        CrosswalkException

      • preferList

        public boolean preferList()
        Description copied from interface: DisseminationCrosswalk
        Predicate: Does this disseminator prefer to return a list of Elements, rather than a single root Element?

        Some metadata formats have an XML schema without a root element, for example, the Dublin Core and Qualified Dublin Core formats. This would be true for a crosswalk into QDC, since it would "prefer" to return a list, since any root element it has to produce would have to be part of a nonstandard schema. In most cases your implementation will want to return false

        Specified by:
        preferList in interface DisseminationCrosswalk
        Returns:
        true when disseminator prefers you call disseminateList().