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/**
 * The contents of this file are subject to the license and copyright
 * detailed in the LICENSE and NOTICE files at the root of the source
 * tree and available online at
 *
 * http://www.dspace.org/license/
 */
package org.dspace.content.crosswalk;

import java.io.IOException;
import java.sql.SQLException;
import java.util.List;

import org.dspace.authorize.AuthorizeException;
import org.dspace.content.DSpaceObject;
import org.dspace.core.Context;
import org.jdom.Element;
import org.jdom.Namespace;

/**
 * Dissemination Crosswalk plugin -- translate DSpace native
 * metadata into an external XML format.
 * 
 * This interface describes a plugin that produces metadata in an XML-based
 * format from the state of a DSpace object.  Note that the object
 * may be an Item, Bitstream, Community, or Collection, although most
 * implementations only work on one type of object.
 *
 * @author Larry Stone
 * @version $Revision$
 */
public interface DisseminationCrosswalk {
    /**
     * XSI namespace, required for xsi:schemalocation attributes
     */
    static final Namespace XSI_NS =
        Namespace.getNamespace("xsi", "http://www.w3.org/2001/XMLSchema-instance");

    /**
     * Get XML namespaces of the elements this crosswalk may return.
     * Returns the XML namespaces (as JDOM objects) of the root element.
     *
     * @return array of namespaces, which may be empty.
     */
    public Namespace[] getNamespaces();

    /**
     * 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.
     *
     * @return SchemaLocation string, including URI namespace, followed by
     * whitespace and URI of XML schema document, or empty string if unknown.
     */
    public String getSchemaLocation();

    /**
     * Predicate: Can this disseminator crosswalk the given object.
     * Needed by OAI-PMH server implementation.
     *
     * @param dso dspace object, e.g. an Item.
     * @return true when disseminator is capable of producing metadata.
     */
    public boolean canDisseminate(DSpaceObject dso);

    /**
     * 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
     *
     * @return true when disseminator prefers you call disseminateList().
     */
    public boolean preferList();

    /**
     * Execute crosswalk, returning List of XML elements.
     * Returns a List of JDOM Element objects representing
     * the XML produced by the crosswalk.  This is typically called when
     * a list of fields is desired, e.g. for embedding in a METS document
     * xmlData field.
     * 

     * When there are no results, an
     * empty list is returned, but never null.
     *
     * @param context context
     * @param dso     the  DSpace Object whose metadata to export.
     * @return results of crosswalk as list of XML elements.
     * @throws CrosswalkInternalException  (CrosswalkException) failure of the crosswalk itself.
     * @throws CrosswalkObjectNotSupported (CrosswalkException) Cannot crosswalk this kind of DSpace
     *                                     object.
     * @throws IOException                 I/O failure in services this calls
     * @throws SQLException                Database failure in services this calls
     * @throws AuthorizeException          current user not authorized for this operation.
     */
    public List disseminateList(Context context, DSpaceObject dso)
        throws CrosswalkException, IOException, SQLException,
        AuthorizeException;

    /**
     * Execute crosswalk, returning one XML root element as
     * a JDOM Element object.
     * This is typically the root element of a document.
     * 
     *
     * @param context context
     * @param dso     the  DSpace Object whose metadata to export.
     * @return root Element of the target metadata, never null
     * @throws CrosswalkInternalException  (CrosswalkException) failure of the crosswalk itself.
     * @throws CrosswalkObjectNotSupported (CrosswalkException) Cannot crosswalk this kind of DSpace
     *                                     object.
     * @throws IOException                 I/O failure in services this calls
     * @throws SQLException                Database failure in services this calls
     * @throws AuthorizeException          current user not authorized for this operation.
     */
    public Element disseminateElement(Context context, DSpaceObject dso)
        throws CrosswalkException, IOException, SQLException,
        AuthorizeException;
}