User Defined Extensions

One of the significant enhancements of the FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998) is the ability of the metadata producer to extend the base standard, through User Defined Extensions, by defining a set of metadata entities and/or elements that are used by a specific discipline or organization. The official requirements and rules for the development of User Defined Extensions are documented in Appendix D of the FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998).

Extended elements to the Standard may be defined by a data set producer or a user community. Extended elements are elements outside the Standard, but needed by the data set producer. If extended elements are created, they must follow the guidelines.

The following rules must be followed when defining extended elements:

• Extended elements must be formally documented within the hierarchical structure of the Standard (Section 0- "Metadata"). When metadata extended elements are used, their existence must be documented in the Metadata Reference Information, element Metadata_Extensions. Every effort should be made to logically organize extended elements within the existing sections and structure. Where there is no logical or natural "fit", new section(s) and/or subsections may be defined.
  
  
• Extended elements must not be used to change the name, definition, type, or domain of a standard element. In particular, an extended element cannot be nested under a data element.
  
  
• Extended elements may be defined as compound and may include extended and standard elements as components. If a standard element is included in an extended compound element, no components of the standard element are changed.
  
  
• Extended elements, like the standard element "Single_Date/Time" may appear in multiple places in the metadata set.
  
  

The basic semantic elements for required for describing a user defined extension are:

• Extended_Element_Name -- (Mandatory) -- the name of the element. The name given to the element must not be the name of any other element in the Standard.
  
• Domain: free text (Do not duplicate any other Standard element name.)
  
  
• Definition -- (Mandatory) -- the definition of the element.
  
• Domain: free text
  
  
• Rationale -- (Optional) -- the reason for creating the Extended element, and its expected uses.
  
• Domain: free text
  
  
• Source -- (Mandatory) -- the name of the entity creating the Extended element.
  
• Domain: free text
  
  
• Type -- (Mandatory) -- the kind of value to be provided, or "compound" if the Extended element contains other elements.
  
• Domain: integer, real, text, date, time, compound
  
  
• Domain -- (Mandatory) -- valid values that can be assigned to the data element. The same rules as those for Standard elements are applied here.
  
• Domain: free text
  
  
• Short Name -- (Mandatory) -- a unique short name consisting of eight alphabetic characters or less.
  
• Domain: free text (Do not duplicate another short name used by the Standard or any other short name in the Extension Registry.)
  
  
• Parent -- (Mandatory) -- The name of the element(s) under which this element may appear. The name(s) may be standard or other extended element(s).
  
• Domain: none, free text (Must be the name of an existing standard or extended element. If the extended element is not part of any other compound element, its parent is the section name as defined by the Standard. If the extended element is defining a whole new section, then its parent is Section 0 - “Metadata”.)
  
  
• Child -- (Mandatory-if-applicable) -- The name of the element(s) which may appear under this element. The name(s) may be standard or other extended element(s).
  
• Domain: none, free text (Must be the name of an existing Standard or extended element.)
  
  
• Rule: production rule for the element, specified using the form given in this Standard.
  
  
  

Below is an example for User Defined Metadata Entities and elements as documented in the FGDC Biological Data Profile of the Content Standard for Digital Geospatial Metadata, FGDC-STD-001.1-1999.

• Extension_Information:
  
  • Name: Bounding_Altitudes
    
  • Short_Name: boundalt
    
  • Type: compound
    
  • Child: Altitude_Minimum
    
  • Child: Altitude_Maximum
    
  • Child: Altitude_Distance_Units
    
  • Parent: Bounding_Coordinates
    
  • Optionality: optional
    
  • Definition: The limits of coverage of a data set expressed by altitude.
    
  • Rationale: To be able to locate the vertical extent of a data set in association with its horizontal extent. The term "altitude" is used instead of the common term "elevation" to conform to the terminology in Federal Information Processing Standards 70-1and 173.
    
  • Source: National Biological Information Infrastructure (NBII), USGS Biological Resources Division, FGDC Biological Data Working Group
    
    
• Extension_Information:
  
  • Name: Altitude_Minimum
    
  • Short_Name: altmin
    
  • Type: real
    
  • Domain: free real
    
  • Parent: Bounding_Altitudes
    
  • Optionality: mandatory
    
  • Definition: The minimum altitude extent of coverage.
    
  • Rationale: To be able to locate the vertical extent of a data set in association with its
    
  • horizontal extent.
    
  • Source: National Biological Information Infrastructure (NBII), USGS Biological Resources Division, FGDC Biological Data Working Group
    
    
• Extension_Information:
  
  • Name: Altitude_Maximum
    
  • Short_Name: altmax
    
  • Type: real
    
  • Domain: free real
    
  • Parent: Bounding_Altitudes
    
  • Optionality: mandatory
    
  • Definition: The maximum elevation extent of coverage.
    
  • Rationale: To be able to locate the vertical extent of a data set in association with its horizontal extent.
    
  • Source: National Biological Information Infrastructure (NBII), USGS Biological Resources Division, FGDC Biological Data Working Group