The GPGIM
The GPlates Geological Information Model (GPGIM) is the first important step in creating a new, more flexible XML way of representing geological data in a plate tectonics context.
The GPGIM provides the fundemental building blocks to enable reconstruction of features through geological time.
The actual XML schema files that form the GPlates Markup Language (GPML) will be essential for the grid computing applications that use it, because it precisely defines the particulars of the language.
However, XML schema files are not the sole support of this grid infrastructure. The information model behind it is doubly important - it must be developed with an eye to preserving backwards compatability, and future-proofed for flexibility.
GPML and Grid Computing
To support collaboration spanning a wide range of different technologies, the language used for communication between grid nodes needs the flexibility and careful planning behind GPML.
Since GPML uses the Geography Markup Language (GML), ISO 19136, which in turn uses XML, it enables collaborative efforts to apply GPML and plate-tectonic reconstruction to any GML-compliant data available from the grid, such as features encoded with GeoSciML, or linking with the Geologic Time Scale developed for it.
Defining the information model through a hierachy of abstract parent classes allows the fundemental components of the model to be described in a very robust way, and allows for features to be easily added later. As the grid expands to include new technologies and software, the language must also be able to expand. GPML also includes the ability to store multiple revisions of the same feature, which serves several purposes:
- Data integrity - revision control ensures that the grid's features can always be reverted to earlier versions, in the event of incorrect data being added.
- Collaboration and data-sharing - the ability for multiple users to access - and modify - the data repository without interfering with each others' modifications.
- Support branching of revision histories - to support speculative experimentation and "what if" scenarios.
Expansion is also supported via GML - this allows for forward compatability with technologies such as the OGC's Web Feature Service (WFS), Web Coverage Service (WCS) and Web Mapping Service (WMS).
The GPGIM also provides for grid nodes that do not support reconstruction natively. GPlates stores all coordinates of features in terms of their present-day position. Storing present-day coordinates along with a plate ID and reconstruction tree allows for easier reconstruction. However, other grid applications may not be able to perform plate tectonic reconstruction themselves; The GPGIM supports these external programs using "Instantaneous" features - snapshots of a feature that have been reconstructed through geological time by GPlates, with their geometry expressed in paleo-coordinates.
Naturally, GPlates and other data grid software must be designed with a high degree of flexibility in their object model. Situations may arise where a new type of feature is required, either from user interaction or via importing data from external sources. For this reason, it is best to see the GPGIM as a dictionary of the most commonly used feature types, or the ontology of concepts which GPlates is able to officially manipulate. This does not rule out additional fringe features created out of necessity or backwards-compatability. Popular feature types not defined in the GPGIM can be added to it as necessary.
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