org.geotools.catalog
Interface MetadataEntity

public interface MetadataEntity

Interface for progamatic access to the Metadata content. This API is used by Catalog to query against CatalogEntry Metadata.

Conceptually a Metadata is comprised of a series of elements. These elements are described by an associated EntityType & Element schema information.

In the best of all possible worlds the EntityType is a member of a well known specification such as ISO19115 (Metadata for spatial data), or ISO19119 (Metadata for Services). GeoAPI kindly provides these abstractions as a series of interfaces, which we are in the process of implementing.

The Metadata interface is similar in use to that of the Feature, it has the same relationship with EntityType that Feature has with FeatureType. By extention Element is similar to AttributeType.

Aside: Many classes that implement Metadata follow Java Bean property conventions to allow for element access. This is not a requirement.

Internationalization: Accounting for internationlization is an interesting problem with metadata.

• One way is to provide a language metadata and only query against Metadata that matches the language you are interested in.
• Another way is to return a "InternationalString" that knows how to write itself out in the Locale you are interested in.
• Consider use of a elements( Locale ) method
• Finally you can ignore the problem

This interface is based on the discussion in the Abstract Catalog specification:

 4.6 Metadata dataset
     Metadta describing a specific dataset [ISO 19101]
 
 4.7 Metadata entity
     Group of metadata elements and other metadata entities describing the same
     aspect of data.
 
 NOTE 1  A metadata entity may contain one or more metadata entities
 NOTE 2  A metadata is equivalent to a class in UML terminology [ISO 19101]
 
 4.8 Metadata schema
     Conceptual schema describing metadata
 
 NOTE ISO 19115 describes a standard for a metadata schema [ISO 19101]
 

Version:

Catalog Services 1.1.1

Author:

ISO 19101, ISO 19115, OpenGIS® consortium

Nested Class Summary

static interface	MetadataEntity.Element Metadata element schema description (name, class, nillable).
static interface	MetadataEntity.EntityType Metadata schema description - the "type" of Metadata.

Method Summary

java.util.List	elements() Access to the values associated with metadata elements.
java.lang.Object	getElement(MetadataEntity.Element element) Gets the value of the provided Element.
java.lang.Object	getElement(java.lang.String xPath) Access to Metadata element values specified by the xPath expression.
MetadataEntity.EntityType	getEntityType() Returns the entity type that describes the schema of this Metadata.

Method Detail

elements

public java.util.List elements()

Access to the values associated with metadata elements. The list is returned in the same order as described by the MetadataEntity.EntityType schema information.

Returns:

List of element values.

getElement

public java.lang.Object getElement(java.lang.String xPath)

Access to Metadata element values specified by the xPath expression. Usually used to return individual objects, if the xPath expression matches multiple elements a List will be returned.

To be clear xPath expression can be used to:

• extract individual members from a List or Array element
• extract individual members from a Map element
• extract individual elements from a nested Metadata

  There is no way at this time to tell the difference between a xPath expression that matches multiple elements, and a xPath expression that matches a single element that happens to be a List. Similarly there is no way to tell if a element had the value null, or if the element did not exist at all. Both these questions may answered by working through the EntityType schema information.

  Parameters:

  xPath - XPath representation of element location.

  Returns:

  element value, List of element value, or null if xPath did not match anything.

getElement

public java.lang.Object getElement(MetadataEntity.Element element)

Gets the value of the provided Element.

Parameters:

element - Element that indicates the value the caller wishes to obtain.

Returns:

The value of the element the parameter represents null if the current Metadata does not contain the Element.

getEntityType

public MetadataEntity.EntityType getEntityType()

Returns the entity type that describes the schema of this Metadata.

Returns:

the entity type that describes the current Metadata object