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Section 3: The Models

Table of contents
  1. 1. 3.1 Design principles adopted

3.1 Design principles adopted

3.2 The producer quality model

3.3 The user quality model

3.4 Using the GeoViQua schemas

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3.1 Design principles adopted

This schema imports existing 19115 schema elements where appropriate, by referencing the 2007 implementation of ISO 19139, at http://schemas.opengis.net/iso/19139/20070417/

Elements of 19115 are replaced by specific GeoViQua documents as follows:

Top‐level schema:

  • GeoViQua_PQM_UQM.xsd

Defines many of the elements of the producer and user quality models, including:

- the GVQ_Metadata root element used by a producer to generate metadata,

- the GVQ_FeedbackCollection root element which may be used to hold the results of a request to the feedback server.

The relationship between these two elements which allows them to be combined in a single document is explained in section 3.4.

Imported schemata

  • ISO 19139 implementation of the 19115 standard
  • 19157_DataQuality.xsd

imported in place of the 19115 ‘dataQuality.xsd’ document (see section 3.1.2).

  • 19115_updates.xsd

imported to allow use of unavailable 19115 elements (see section 3.1.1).

  • uncertml.xsd

imported to allow use of UncertML elements to describe quantified uncertainty (see section 4.5)

  • GeoViQua_DataQuality.xsd

Contains all the remaining GeoViQua‐specific elements for the producer model – often these consist of extensions to ISO 19157.

Throughout the new documents, the OGC approach of allowing a ‘nilReason’ attribute for missing element values has been adopted. In practice, this leads to elements looking as follows:

CI_Responsible.png

OGC‐recommended values for ‘nilReason’ are as follows:

nil_ReasonRecomendations.png

This approach may change depending on the ultimate implementation style of the 19157 data quality schema. Several possible approaches for nillable or voidable stereotypes exist, and it is likely that we will follow the approach recommended by INSPIRE. It should also be possible to relax application of the stereotype for elements which are truly optional.

PropertyType.png

Figure 8. Relationship between the type and the nillable ‘PropertyType’ in OGC schemas

The mechanism to allow this behaviour consists of the declaration of a wrapper ‘ElementName_PropertyType’ for each element type, containing a reference to the named element type, plus the gco:nilReason attribute. This ‘x_PropertyType’ is then referenced as the type for schema elements, as shown above in Figure 8.


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