Sensor Metadata

1 Introduction

OpenGeospatial Consortium (OGC) has development two important metadata. One is SensorML for sensors and the other is Observations and Measurements for sensor observations and measurements. We will introduce them briefly here. Also, we will briefly introduce the Harmonization and Crosswalking metadata.

2 SensorML

Sensor Model Language (SensorML) establishes the general model and XML encoding for sensors. SensorML provides a standard means by which sensor and platform capabilities and properities can be published and discovered in a “Sensor Web”. SensorML provides an XML schema for defining the geometric, dynamic, and observational characteristics of a sensor. The basic XML schema structure for a sensor is shown as the following:

Figure1. Basic XML Schema Structure for a Sensor

For the given sensor xml encoding, there are several element sections shown above. Not all elements need to be included for a given sensor xml encoding. Some of elements can be tailored as required when encoding a specialized sensor. A sensor system is composed of the sensor and its platform. A sensor may be attached to a platform. Within SensorML, platforms and sensors are treated as separate entities that share an association with one another. The basic relationship between sensors and platforms is as Class Diagram show below:

Figure2. Basic Relationship Between Sensors and Platforms

3 Observations and Measurements

OGC Observations and Measurements (O&M) provides a general models and XML encoding for sensor observations and measurements. An observation involves a procedure to determine the value, which may involve a sensor or observer, analytical procedure, simulation or other numerical process. An observation results in an estimate of the Value of a property or phenomenon related to the target of the observation. Values are of various data types, including the primitive types category, quantity, count and Boolean, time, location and geometry. The value normally requires a reference system to provide the context for its interpretation and valid operations on it. Common reference systems are the unit of measure for a quantity, a dictionary or “code space” for a category, a spatial reference system for location and geometry, and a temporal reference system for time values. Observed values may have other properties, such as quality indicators.

XML schema structure is shown as the following:

Figure3. XML Schema Structure

General UML diagram for observation is shown here:

Figure4. General UML Diagram

An observation has a timestamp, since the Observation feature describes and act or “observation event”. An observation has a using property, the value of which is a description of a procedure such as instrument or observer. A model and encoding for the functional description may be a sensor. The target property contains or points to the specimen, region or station, which is the object of the observation. The property indicates the result of the observation.

4 Harmonization and Crosswalking

Different systems may use different metadata standers and even use many metadata standers in the same system. One of the inherent attribute of metadata is domain-related, that brings great difficulties in integration and sharing. So far, the key approach is mapping.

There are some different levels of mapping, the semantic level mapping, the structure-level mapping, the language based mapping, and the constraint-based mapping. Usually, a standard mapping is to find the semantic and relationship correspondences between elements of two standards.