Latest revision as of 14:41, 12 February 2018

DMF metadata elements

General

Viewpoints

The DGIWG Metadata Vision defines a general metadata use case involving metadata elements in four different contexts (i.e. use case scenarios):

• Discovery concerns the most important metadata elements, i.e. the metadata elements involved when a user needs to discover existing resources;
• Evaluation concerns the metadata elements needed to understand whether the discovered resources meet the user requirements;
• Use concerns the metadata elements needed to access and use the resource;
• Management concerns the metadata elements needed to manage the existing resources.

From a user viewpoint, the involved DMF metadata elements depend on these four contexts. Four viewpoints corresponding each to one of these four contexts are expressed here as sets of metadata elements applicable to the specific context.

Metadata element sets

The DMF metadata elements document different aspects of the resources including their identification, the related quality information, the spatial representation and the content description of the resource data. Each aspect is dealt with by the definition of an identified element set grouping the metadata elements covering the documentation of the aspect.

This grouping mechanism is important for the users especially when the number of metadata elements to be considered becomes high.#

Metadata classes

• DMF/Core defines the minimum set of metadata elements to be implemented by any metadata catalogue. This set satisfies the discovery use case.
• DMF/Common is an additional set of metadata elements for a more complete description of any type of resource supported by DMF. It extends DMF/Core and covers discovery and basic evaluation use cases.
• DMF/Services extends DMF/Core for service metadata and can be used together with DMF/Common (i.e. it is possible to use DMF/Services on top of DMF/Core (if DMF/Common elements are not needed) or on top of DMF/Common for an extensive profile).
• DMF/Data extends DMF/Common for data related resources (i.e. dataset, series and tile). DMF/Data adds metadata elements for evaluation and use.
• DMF/Data+ extends DMF/Data for the implementation of coverage quality results and other metadata elements introduced in ISO 19115-2 but having some applications for any geospatial product.
• A DMF/Sensor class extending DMF/Data for sensors.
• DMF/Defence extends DMF/Core or DMF/Common for military oriented needs including NATO needs (extensions defined in NGMP, particularly security). It is needed to handle metadata to be exchanged with NATO in conformance with NGMP. DMF/Defence can be implemented with DMF/Core and possibly any other metadata class.
• DMF/Specific is an extension of the ISO metadata standards for high level military implementation of the DMF metadata elements.

Metadata element requirements

Each DMF metadata element pertains to one metadata class. Each metadata element of the DMF has:

• A unique Identifier introduced for consistency of the documentation;
• A Title serving as a human-oriented comprehensive identifier;
• An indication of the related metadata class;
• A Description statement which may include the expression of constraints (preceded by “Constraints:”) applicable to the metadata element;
• A Value Domain defining the applicable data types and vocabularies, as well as the applicable restrictions of the domain of values. Individual values are expressed in bold.
• A Cardinality statement.

Each basic type and vocabulary also pertains to one metadata class. Some data types are complex, i.e. they comprise of a set of properties also having an identifier, a title, a description, an indication of the related metadata class, a value domain and a cardinality. A complex data type implicitly pertains to the metadata classes defined for its properties (i.e. the complex type properties may relate to different metadata classes).

The cardinality statement may be expressed as:

• a number of occurrences (typically 1 indicates that one and only one occurrence is expected), or;
• a range expressing a minimum and maximum number of occurrences. The format of a range of occurrences is n…m where:
• n is a positive integer or 0 indicating that the field is optional, i.e. it may not occur on any resource;
• m is a positive integer or * indicating that the maximum is unbounded.

The cardinality statement defines the minimum and maximum number of occurrences of the DMF metadata elements in terms of relevance for the types of resources supported by DMF. A metadata element is optional (i.e., its minimum occurrence is set to 0) when it may not occur when documenting any resource in the scope of DMF. Constraints are expressed when the relevance of the metadata elements is specific to some resource types or depends on the value of other metadata elements.

The constraints applicable to DMF profiles with respect to the cardinality of the metadata elements are part of the rules for profiling defined in Annex A.

The following documentation of the DMF metadata elements is composed of:* The overview of the DMF metadata elements (see clause 5.2) which expresses the identifier, the title, the metadata class and the cardinality statement of the DMF Metadata Elements. It also organizes the metadata elements into four different viewpoints

• The detailed description of the DMF metadata elements organised by metadata element sets (see clause Error: Reference source not found).

Metadata Element Overview

For a detailed description of the metadata elements see clause 5.3.