Treatment of Mandatory Properties

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9.1.3 Observations as a Data-type

Throughout the model the Observation class is used as the data-type for estimated property values, allowing them to be attributed with meta-data about the value’s provenance and quality. This is important as a soil property may be measured in several ways, to differing levels of quality, and both affect how values are interpreted or processed. Using OM to explicitly decouple procedures, properties and results keeps the number of properties defined in the model manageable. Otherwise, the common practice of defining a property as a combination of the phenomenon observed, how it was measured, for example pH_NaCl and pH_KCl both describe soil pH, but using different procedures, causes significant increase in properties defined. This not only introduces an inconsistency with OM, but also reduces interoperability and creates a governance overhead, requiring the core information model to be updated for newly developed processes.

9.2 Conceptual Model

The conceptual model is designed as a technology neutral representation of the semantics of the soil domain. It is defined using UML and describes four aspects of the domain: 1. the description and classification of soil; 2. the soil profile; 3. sampling and fieldlaboratory observations; and 4. sensor-based monitoring of dynamic soil properties. In accordance with the use cases defined for this Interoperability Experiment it excludes: — soil mapping; and — landscape, land-use, climate and vegetation data these are recognized as important, but best modelled in collaboration with experts from those domains. A set of utility classes was defined in this model to provide placeholders for complex data types and classes and are described in Annex C. A soil Figure 1 is a body of unconsolidated mineral and organic material developed through soil forming processes near the surface of the earth. It is composed of horizons defined according to their physical, chemical or biological characteristics. Horizons are given a designation according to their character and position and a soil can then be classified according to one of a number of soil taxonomies addressing a soil’s form or function. Copyright © 2016 Open Geospatial Consortium. 21 A description of a soil comprising a vertical section of horizons is called a soil profile Figure 2. Soil profiles usually describe a sequence at a sampling location for example, an excavation but this definition may be extended to include aggregate descriptions such as a soil profile class of the expected variation of soil properties over a mapped area. Parts of a soil may be extracted and analyzed, either immediately in the field, or by subsequent analysis of a physical sample in a laboratory Figure 3. It is essential to be able to record the method of sampling and analysis, and the quality or uncertainty of the resulting measurement. The results of these measurements may be presented and used in their own right or be incorporated into a soil description. In contrast to inherent soil properties that change very little, certain soil properties change in response to external forces over measurable human-scale periods of time. These dynamic properties are essential to understanding soil, and broader environmental Figure 1 — An exposed section of soil in farmland. This soil is classified, according to the New Zealand Soil Classification, as a ‘Podzol Soil’. Image copyright of Landcare Research. All rights reserved. Permission from Manaaki Whenua: Landcare Research New Zealand Limited must be obtained before the re-use of this image. conditions and health, particularly where change is a function of human activity for example land use or management practices. Change over time may be monitored through a variety of techniques from episodic visits to established monitoring sites or