19.7 Schema information

Introduction

GeoNetwork is able to handle several metadata schema formats. Up to now, the supported schemas are:

  • ISO-19115 (iso19115): GeoNetwork implements an old version of the draft, which uses short names for elements. This is not so standard so this schema is obsolete and will be removed in future releases.

  • ISO-19139 (iso19139): This is the XML encoding of the ISO 19115:2007 metadata and ISO 19119 service metadata specifications.

  • Dublin core (dublin-core): This is a simple metadata schema based on a set of elements capable of describing any metadata.

  • FGDC (fgdc-std): It stands for Federal Geographic Data Committee and it is a metadata schema used in North America.

In parenthesis is indicated the name used by GeoNetwork to refer to that schema. These schemas are handled through their XML schema files (XSD), which GeoNetwork loads and interprets to allow the editor to add and remove elements. Beside its internal use, GeoNetwork provides some useful XML services to find out some element properties, like label, description and so on.

xml.schema.info

This service returns information about a set of schema elements or codelists. The returned information consists of a localised label, a description, conditions that the element must satisfy etc...

Request

Due to its nature, this service accepts only the POST binding with application/XML content type. The request can contain several element and codelist elements. Each element indicate the will to retrieve information for that element. Here follows the element descriptions:

  • element: It must contain a schema and a name attribute. The first one must be one of the supported schemas (see the section above). The second must be the qualified name of the element which information must be retrieved. The namespace must be declared into this element or into the root element of the request.

  • codelist: Works like the previous one but returns information about codelists.

<request xmlns:gmd="http://www.isotc211.org/2005/gmd"> 
    <element schema="iso19139" name="gmd:constraintLanguage" /> 
    <codelist schema="iso19115" name="DateTypCd" /> 
</request>

Note

The returned text is localised depending on the language specified during the service call. A call to /geonetwork/srv/en/xml.schema.info will return text in the English language.

Response

The response’s root element will be populated with information of the elements/codelists specified into the request. The structure is the following:

  • element: A container for information about an element. It has a name attribute which contains the qualified name of the element.

    • label: The human readable name of the element, localised into the request’s language.

    • description: A generic description of the element.

    • condition [0..1]: This element is optional and indicates if the element must satisfy a condition, like the element is always mandatory or is mandatory if another one is missing.

  • codelist: A container for information about a codelist. It has a name attribute which contains the qualified name of the codelist.

    • entry [1..n]: A container for a codelist entry. There can be many entries.

      • code: The entry’s code. This is the value that will be present inside the metadata.

      • label: This is a human readable name, used to show the entry into the user interface. It is localised.

      • description: A generic localised description of the codelist.

<response> 
    <element name="gmd:constraintLanguage"> 
        <label>Constraint language</label> 
        <description>language used in Application Schema</description> 
        <condition>mandatory</condition> 
    </element> 
    <codelist name="DateTypCd"> 
        <entry> 
            <code>creation</code> 
            <label>Creation</label> 
            <description>date when the resource was brought into existence</description> 
        </entry> 
        <entry> 
            <code>publication</code> 
            <label>Publication</label> 
            <description>date when the resource was issued</description> 
        </entry> 
        <entry> 
            <code>revision</code> 
            <label>Revision</label> 
            <description>date identifies when the resource was examined 
                or re-examined and improved or amended</description> 
        </entry> 
    </codelist> 
</response>

Error management

Beside the normal exceptions management, the service can encounter some errors trying to retrieve an element/codelist information. In this case, the object is copied verbatim to the response with the addition of an error attribute that describes the encountered error. The returned errors are described in Table 19.6, “Possible errors returned by xml.schema.info service”. Here follows an example of such response:

<response>
    <element schema="iso19139" name="blablabla" error="not-found"/>
</response>

Table 19.6. Possible errors returned by xml.schema.info service

Error code

Description

unknown-schema

The specified schema is not supported

unknown-namespace

The namespace of the specified prefix was not found

not-found

The requested element / codelist was not found



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