Latest revision as of 13:21, 6 July 2016

This page aims to explain how to publish ISO metadata using legacy GIS library org.gcube.common.geoserverinterface (referred as GeoServerInterface from now on).

Since various components still rely on GeoServerInterface to publish geo-referenced data, the library has been enhanced to facilitate publication of ISO Metadata correctly filled (see GCube Object Metadata).

This guide require the reader to already know the functionality of GeoServerInterface library.

Maven Dependency

The GeoServerInterface library is released as a maven artifact with the following coordinates

<groupId>org.gcube.common</groupId>
<artifactId>geoserverinterface</artifactId>

Please note that ISO Metadata facilities are released from version 1.10.2.

ISO 19115:2003 metadata compliance

Metadata objects used by the libraries implement GeoAPI interfaces, which are fully compliant to ISO 19115:2003/19139. Current implementation is based on GeoToolkit Metadata module.

Code Adaptation

Introduced enhancements have been designed in order to make code adaptation as easy as possible from developers view. The class org.gcube.common.geoserverinterface.GeoCaller remains the main entry point of GeoServerInterface library for publishing means.

Preexistent publishing methods have been doubled in a way that users just need to change the passed arguments in order to change ISO Metadata publishing behavior.

The following is the list of newly introduced methods

public boolean addGeoLayer(String fileUrl, String layerName, String layerTitle, String workspace, GeonetworkCategory category, Metadata toPublishMeta, String scope, String defaultStyle) throws Exception;
public boolean addFeatureType(FeatureTypeRest featureTypeRest,String defaultStyle, GeonetworkCategory category, Metadata toPublishMeta) throws Exception;
public boolean addGeoTiff(String geoTiffUrl, final String layerName, String layerTitle, final String workspace, GeonetworkCategory category, Metadata toPublishMeta, String scope, String defaultStyle) throws Exception;
public boolean addPreExistentGeoTiff(String fileName, final String layerName, String layerTitle, final String workspace, GeonetworkCategory category, Metadata toPublishMeta,String defaultStyle) throws Exception;

To summerize difference in methods signature :

• removed argument String description
• removed argument String abstract
• added argument org.opengis.metadata.Metadata toPublishMeta : ISO Metadata object representation. It must be already filled with all needed information but layer OGC links, which will be generated at publishing time by the library.
• added arguemnt String defaultStyle : the defaultStyle to be used when generating OGC links in ISO metadata

Instances of org.opengis.metadata.Metadata interface can be arbitrarily generated by the invoking application. However, the library has been provided with facilities to easily generate Metadata instances for most gCube applications needs.

Metadata generation facilities

Instances of org.opengis.metadata.Metadata interface can be generated in very different ways. However, we identified a common set of information which every application should include in its published metadata. Providing a common way to generate these metadata entry aims to :

• Reduce the needed effort to generate metadata from the developer's point of view;
• Reuse of code;
• Common behavior to gather common information (see #Infrastructure configuration);
• Check project's constraints (see GCube Object Metadata).

GcubeISOMetadata class

The utility class org.gcube.common.geoserverinterface.bean.iso.GcubeISOMetadata lets developers to simply specify the metadata information strictly needed for the generation, relying on internal logic for generic behavior.

Instantiating

A GcubeISOMetadata instance should be generated for each publishing request, but this behavior depends on the caller application logic. At construction time, common information fetched from the gCube IS is loaded. Queries to IS are done via the ic-client, so be sure that a proper scope is setted via org.gcube.common.scope.api.ScopeProvider. Loaded configuration is represented by instances of the class org.gcube.common.geoserverinterface.bean.iso.EnvironmentConfiguration see #EnvironmentConfiguration class.

import org.gcube.common.geoserverinterface.bean.iso.EnvironmentConfiguration;
import org.gcube.common.geoserverinterface.bean.iso.GcubeISOMetadata;
import org.gcube.common.scope.api.ScopeProvider;
....
ScopeProvider.instance.set(...);
GcubeISOMetadata meta=new GcubeISOMetadata();
EnvironmentConfiguration configuration = meta.getConfig();
System.out.println("Current configuration is "+configuration);

Filling parameters

The GcubeISOMetadata class exposes setter/add methods to let users specify metadata information. The following is a list of attributes that can be set along with their cardinality. Attributes which cardinality can be more then 1 are setted via the related addXXX() method, while setXXX() methods are provided for the other ones.

The following snippets shows how this parameters are set :

import org.gcube.common.geoserverinterface.bean.iso.EnvironmentConfiguration;
import org.gcube.common.geoserverinterface.bean.iso.GcubeISOMetadata;
import org.gcube.common.geoserverinterface.bean.iso.Thesaurus;
import org.geotoolkit.metadata.iso.extent.DefaultExtent;
import org.opengis.metadata.citation.PresentationForm;
import org.opengis.metadata.identification.TopicCategory;
import org.opengis.metadata.spatial.GeometricObjectType;
import org.opengis.metadata.spatial.TopologyLevel;
 
...
 
GcubeISOMetadata meta=new GcubeISOMetadata();
//Setter methods
meta.setAbstractField(...);
meta.setCreationDate(...);
meta.setExtent(DefaultExtent.WORLD);
meta.setGeometricObjectType(GeometricObjectType.SURFACE);
meta.setPresentationForm(PresentationForm.MAP_DIGITAL);
meta.setPurpose(...);
meta.setResolution(...);
meta.setTitle(..);
meta.setTopologyLevel(TopologyLevel.GEOMETRY_ONLY);
meta.setUser(...);						
 
//Add methods
meta.addCredits(..);
meta.addGraphicOverview(...);
 
//Need to get keywords referred Thesaurus
Thesaurus generalThesaurus=meta.getConfig().getThesauri().get(...);		
meta.addKeyword(..., generalThesaurus);
meta.addKeyword(..., generalThesaurus);
 
 
meta.addTopicCategory(TopicCategory.BIOTA);

Getting the metadata

Once the metadata information have been set to the GCubeISOMetadata instance, the caller can obtain the metadata to publish just by calling its public org.opengis.metadata.Metadata getMetadata() method. In case any mandatory value is missing a MissingInformationException is thrown.

ScopeProvider.instance.set("/gcube/devsec");
GcubeISOMetadata meta=new GcubeISOMetadata();
 
// Set information
....
 
// Print out the metadata
XML.marshal(meta.getMetadata(),System.out);

Extending default behaviour

GCubeISOMetadata class can be extended in order to enhance its purpose and behaviour. In the following example we define our MyApplicationIsoMetadata class in order to :

• Automatically set application default values when instatiating;
• Add new mandatory fields to generate data quality information to our metadata, via :
  • Adding new member to our class
  • Override of protected method checkConstraints
  • Override of public method getMetadata()

import org.gcube.common.geoserverinterface.bean.iso.GcubeISOMetadata;
import org.gcube.common.geoserverinterface.bean.iso.MissingInformationException;
import org.opengis.metadata.Metadata;
 
//Extends org.gcube.common.geoserverinterface.bean.iso.GcubeISOMetadata
public class MyApplicationIsoMetadata extends GcubeISOMetadata {
 
	//We want this citation to be automatically added to credits
	private static final String applicationCitation="....";
 
 
	//Our mandatory field
	private String mandatoryField=null;
 
	public MyApplicationIsoMetadata() throws Exception {
		//Let the super class initialize itself
		super();
		//Let's add our citation to credits
		this.getCredits().add(applicationCitation);
	}
 
	@Override
	protected void checkConstraints() throws MissingInformationException {
		// We let the super class to perform its checks before continuing
		super.checkConstraints();
		// Custom check against mandatoryField
		if(mandatoryField==null) throw new MissingInformationException();
	}
 
	@Override
	public Metadata getMetadata() throws URISyntaxException,MissingInformationException {
		Metadata toReturn=super.getMetadata();
		//We set our mandatory field to the metadata
                ........
		return toReturn;
	}
 
	public String getMandatoryField() {
		return mandatoryField;
	}
 
	public void setMandatoryField(String mandatoryField) {
		this.mandatoryField = mandatoryField;
	}
}

Infrastructure configuration

Common metadata values (i.e. project citation, project name etc.) are loaded from a gCube generic resource that must be accessible in the current scope. The given generic resource's body must contain an XML Serialization of #EnvironmentConfiguration class.

Configuring IS interaction

The gcube generic resource is found submitting a query to the ic-client with the following parameters.

• Secondary Type [default value = ISO]
• Resource Name [default value = MetadataConstants]

The Generic resource is cached to avoid overhead in querying the IS. The cache TTL, along with the query parameters value can be configured by editing the #Properties file.

EnvironmentConfiguration class

The class org.gcube.common.geoserverinterface.bean.iso.EnvironmentConfiguration represents the metadata constants declared for the entire project.

Parameters

Thesaurus class

Thesaurus class represents a thesaurus declaration for a given keyword set in ISO metadata (see ISO 19115:2003/19139).

The following is the list of its members.

Publishing Configuration

GeoServerInterface library allows administrator to easily configure their environment constants. The following snippets shows how :

import org.gcube.common.geoserverinterface.bean.iso.EnvironmentConfiguration;
import org.gcube.common.scope.api.ScopeProvider;
import org.gcube.common.resources.gcore.GenericResource;
....
//Create the configuration
EnvironmentConfiguration config=new EnvironmentConfiguration();
//Set all the values in the configuration
...
//We set the scope where to Publish the configuration
ScopeProvider.instance.set(...);
//Let's actually publish the configuration
GenericResource res=config.publish();
//Just some output log here
String id=res.id();
System.out.println("Published configuration [res ID = "+id+"] under scope "+ScopeProvider.instance.get());

The method config.publish() creates and publishes a generic resource with the configured name and secondary type (see #Properties file).

Properties file

Configuration of GeoServerInterface library's behaviour can be done by editing the geoserverInterface.properties file distributed inside the library.

The following parameters affects ISO Metadata logic behaviour: