Define a generalised class for Observations on features

[cookeac]

Define a generalised class for Observations on features that avoids the full complexity of OGC/ISO Observations & Measures service, but can be subclassed to support specific observations.

This issue is part of #39

[cookeac]

Initial suggestion is to define an ObservationType that forms the basis for various concrete resources for observations. That is, to create new class of observation, you create a JSON Schema file and use anyOf to include the ObservationType class.

Attributes could be as follows:

Property	Type	Source	Description
id	string	ResourceType	Unique identifier (UUID) used within the current server to identify the resource.
identifiers	array of IdentifierType	"	Identifiers for the resource (see well-known/schemes... for example identity schemes).
links	array of RelationType	"	Linked resources that are related to the current resource.
meta	MetaDataType	"	Meta-data for the resource. Mandatory if you wish to support synchronisation.
name	string	"	A user-readable name for the resource.
@self	string	"	Uniform resource identifier (URI) of the resource (rel=self). Mainly used to support JSON-LD.
observationDate	ISODateTime	ObservationType	Defines the date and time of the observation in UTC (must include the Z timezone for clarity). ISO19156 "resultTime"
phenomenonTime	ISOPeriod	"	If specified, describes a potentially broader period the observation represents.
feature	FeatureReferenceType or RelationType	"	Identifies the feature to which the observation relates (should this be an array?). ISO19156 "featureOfInterest" ]
holding	FeatureReferenceType or RelationType	"	Identifies the holding on which the observation was recorded (could be accomplished with links[]?)
responsible	string	"	Identifier for the person who carried out the activity, made or recorded the observation.
remark	string	"	Remarks or notes about the observation.