<Li> result time--the time when the result was generated </Li> <Li> valid time--the period during which the result may be used </Li> <P> The key to the model is the division of the observation and its feature of interest, separating the concerns so that the appropriate information associated with the description of each object . This allows a unified treatment of in situ, ex-situ, and remote - sensed observations . The observation schema may also be understood as a corollary of the General Feature Model from ISO 19101, providing metadata associated with the estimation of the value of a feature property . The Observation model takes a user - centric viewpoint, emphasizing the semantics of the feature - of - interest and its properties . This contrasts with sensor oriented models such as SensorML, which take a process--and thus provider - centric viewpoint . </P> <P> Many observations are made to detect the variation of some property in the natural environment, expressed as a spatial function or field, also known as a coverage (ISO 19123: 2005). The relationship between observations, features and coverages is explained, in the context of ocean observations and modeling, in a report for GEOSS Architecture Implementation Pilot 3 . </P>

What is the difference between a measurement and an observation