string

boolean

integer

double

anyURI

gpml:featureId

• GPML Feature Ids are the unique identifiers used for anything with a gpml:featureId[1] identity property, i.e. anything that derives from gpml:AbstractFeature. They must be unique for every feature, generated at creation time and remain unchanged for the lifetime of the feature.
• As an example, the unique id process used by GPlates draws from several sources of uniqueness, including Local time, Internal incrementing integer from this session, User id, Hostname, and Process Id. For example: GPlates-2263390205.0-jboyden.aurora.28095. Note that this is only an example of the process GPlates uses to create a unique identifier - the GPGIM only specifies that the id must be unique and remain constant for every gpml:Feature.
• The final featureId string should be restricted to the characters that are acceptable for XML Ids: http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/#Id

gpml:revisionId

• GPML Revision Ids are the unique identifiers used for the specific revisions of gpml:AbstractFeatures. They must be unique for each revision, generated at revision creation time.
• The final revisionId string should be restricted to the characters that are acceptable for XML Ids: http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/#Id

gpml:plateId

• Unique Id for a group of features that rotate in unison. Used in all ReconstructableFeatures via the .reconstructionPlateId property. See also TotalReconstructionSequence and AbsoluteReferenceFrame. They are represented by an unsigned long integer.

xs:any

gml:Point

gml:TimeInstant

gml:TimePeriod

gml:LineString

• gml:LineString is here as a placeholder only; in the GML schemas, properties such as centerLineOf will use gml:_Curve, although we expect to be dealing with LineStrings primarily.
• Note that the GPGIM is not GPML; The primary purpose of this document is to be the information model for GPlates, but not get tied down to one particular implementation of that model (e.g. XML, C++). Hence, it does not authoritatively talk about structures external to the GPGIM.

gml:Vector

gml:Polygon

gpml:measure

• maps to gml:MeasureType, which extends double and adds the requirement for a uom attribute indicating the units used.

gpml:angle

• represents an angle measurement. maps to gml:MeasureType, which bestows the ability to use the uom= attribute on the property, which in this case will likely be (degrees)

gml:_MetaData

gml:_Geometry

gml:AbstractFeature

• Note: all the properties listed here are for convenience only; we inherit many properties upstream from GML, useful things like gml:name and gml:description. There are many more that are not listed here which may come in handy.
• For example, there are two attributes (not properties) which will be essential for GPlates:
• srsName= For indicating the geocentric/geodetic ellipsoid approximation of the earth, for the coordinates used by geometry of this Feature- i.e. WGS84.
• frame= For indicating the geological time scale that was used to determine temporal position of this Feature. I believe we'll actually be using the 'frame=' attribute in gml:TimePeriod.{begin,end} or gml:TimeInstant.timePosition

• contains external gml:_MetaData[0..*] gml:metaDataProperty
  • The gml:metaDataProperty can contain almost completely arbitrary markup, thanks to the use of <xs:any>.
• contains external string[0..1] gml:description
  • Again, a 'hidden but useful' property inherited from GML.
• contains external string[0..*] gml:name
  • More than one gml:name can be assigned, the distinction between two names being handled by the 'codeSpace=' attribute of gml:name.
  • gml:name is actually found in the gml:AbstractFeatureType side of things, I just include it here so these 'hidden but useful' properties can be shown.

gml:AbstractFeatureCollection

gml:AbstractMetaData

gml:AbstractGeometry

FeatureCollection

- This is the root element for GPML data files, and is the way GML groups all other Features together. It contains these features via the gml:featureMember property.

• contains external AbstractFeature[0..*] gml:featureMember
  • We inherit a property similar to this from gml:AbstractFeatureCollection. In the case of GPML we will be filling it with anything that derives from gpml:AbstractFeature, although there's nothing stopping other GML-compliant features from being bundled up with our own.

AbstractFeature

- Highest-level abstract parent of all GPML Features.

• contains const gpml:featureId[1] identity
  • GPlates enforces a mandatory unique Id for each Feature. See gpml:featureId for more information.
  • gml:name with a specific codespace was considered, but in this case we want to ensure specific Features have such an Id.
• contains const gpml:revisionId[1] revision
  • All GPlates Features also have a revision Id. When a feature is modified by a user, it gets a new revision Id, and its list of superseded revisions is updated. This way we can do some important book-keeping to help us in situations where multiple feature collections are loaded/modified/saved/unloaded.
• contains gpml:revisionId[0..*] supersededRevision
  • This lists all revisions of this feature that were superseded by this one. This is a more accurate way of keeping track of the past, older revisions of a feature.
  • It will be purged on occasion to ensure files do not get bloated from many small changes. Newly superseded revisionId s get unshifted onto the front/head of the list, older ones are at the end/tail of the list.
  • a simple linear 'version number' would fail if a feature collection was concurrently modified by multiple users and then merged.
• contains OldPlatesHeader[0..1] oldPlatesHeader
  • Since a Feature in GPML will often correspond to a PLATES polyline (if a PLATES file was the original source of data), we include an optional reference to a Plates-compatible header object. This is used to keep metadata around if we import from a PLATES data file.
• contains string[0..*] subcategory
  • Every gpml:Feature can optionally have one or more subcategories assigned to it. These are free-form text strings, and behave very similarly to the gml:name property; they also possess a 'codeSpace=' attribute to indicate what convention was used when assigning this subcategory to this Feature.
  • Use of the .subcategory property is entirely optional, however it is useful in several situations. There are many possible subcategories of real-world:Features, and these are highly subjective, depending on scientist, dataset, and area of research. Permitting arbitrary subcategorisation in the GPGIM has two benefits. One, GPlates can to continue to treat those real-world:Features as the appropriate gpml:Feature since any subcategory must have the same properties as the parent gpml:Feature. Two, it allows the scientist to have a finer grain of control over the categorisation of those real-world:Features without messing around with XML trying to extend the GPGIM.
  • An example: Seamount s and Guyot s. A Guyot is a special case of Seamount with a flat top. Functionally, they are identical. A problem arises; do we create a GPGIM feature for both of them, or just use Seamount for both cases? Some scientists and datasets may not care about the distinction, and wish to treat everything as a gpml:Seamount without being forced to go over the data and classify everything. On the other hand, a "Guyot Expert" would be very interested in the distinction between the two. The .subcategory property allows you to do this, without forcing you to.

TimeVariantFeature

• TimeVariantFeature is one of the parents to the majority of commonly used gpml:Features.
• Most, but not all, features will ultimately inherit from our gpml:TimeVariantFeature in order to have the .validTime property. In contrast, features deriving from InstantaneousFeature require a TimeInstant rather than a TimePeriod, and they obtain this via the .reconstructedTime property.

• contains gml:TimePeriod[0..1] validTime
  • The validTime parameter defines the position of this feature on the geological timescale.
  • Some Features may only exist between (say) 120Ma and 100Ma, others will be represented as a series of distinct Features, i.e. a MidOceanRidge at (lat,long) between 200Ma-160Ma and another MidOceanRidge (which happens to model the same physical thing) at (lat,long) between 160Ma-0Ma, perhaps due to it having radically different properties. Generally, it is preferable to use GPML's time-dependent properties where applicable, but since we will be importing PLATES data, this 'slicing' of features will be commonplace in real datasets.
  • Note that if a gpml:Feature is a ReconstructableFeature, it might potentially have more gml:TimePeriod s recorded in its .reconstructionPlateId property, as it is a time-dependent property. The validTime that we specify here should still be used as the master indication of the Feature's lifetime.

InstantaneousFeature

- "Snapshot" version of GPML Features, defined at a specific time

• Most of the ReconstructableFeature tree is copied here. Instantaneous versions of gpml:Features are designed for export to other programs, which would have difficulty doing reconstructions themselves.
• These features have different properties to their Reconstructable counterparts. Aside from the "big one" of not being rotatable via the action of Finite Rotations, their geometry is defined in terms of a specific time (.reconstructedTime) rather than being defined in present-day terms. This distinction also becomes more important with time-variant property values.
• In comparison to ReconstructableFeature:-
• - must be defined for only an instant.
• - must have its geometry specified in its time-of-definition position (the time-of-definition may or may not be the present-day)
• - will not have a gpml:reconstructionPlateId
• Note, No properties of an InstantaneousFeature will be time-dependent!
• Like ReconstructableFeature, InstantaneousFeatures should have at least one geometric presence.

• contains FeatureSnapshotReference<TimeVariantFeature>[0..1] derivedFrom
  • an optional link to the ReconstructableFeature this Instantaneous snapshot was taken from, for historical interest.
• contains gml:TimeInstant[0..1] reconstructedTime
  • the TimeInstant corresponding to the moment this InstantaneousFeature was converted from its Reconstructable original.
  • Normal GPlates Features store their geometry in present-day coordinates, and store reconstruction information to rotate them into paleo-coordinates. However, for exporting data into other GPML aware programs, i.e. GMT, it is necessary to do the rotations on behalf of the external application. The .reconstructedTime property of the Instantaneous feature records what time this Feature was reconstructed to by GPlates, (in Ma or whatever 'uom' and 'frame' you want in the TimePeriod).
• contains gml:TimePeriod[0..1] validTime
  • Instantaneous features only really exist for a single instant, the TimeInstant in the reconstructedTime property, set when a snapshot is made of a ReconstructableFeature. The 'TimePeriod validTime' property of the ReconstructableFeature is no longer applicable.
  • However, the original information about the features' lifespan is still useful information. Isochrons in particular measure their age as their time-of-appearance. This information would be lost in InstantaneousIsochron snapshots unless the information is copied to this .validTime property.
  • This property may at first glance appear to be identical to TimeVariantFeature.validTime, and it is true that the value of this property should be the same; however it serves a different purpose (useful record of original data) and is in fact an entirely different .validTime property with a TimePeriod value.
• contains gpml:plateId[0..1] reconstructedPlateId
  • in the spirit of not throwing away information, the plateId at time of conversion to an InstantaneousFeature type is recorded here. Unlike ReconstructableFeature.reconstructionPlateId, this is not a time-dependent property, and will only ever refer to one gpml:plateId.