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Part III. Appendix 2: Data TransportThe FSDM consists of approximately 140 classes of objects that describe, contain, and/or manipulategeospatial data. One of the key features of this model is the separation of data storage from itsgeometry and topology. The geometry and topology information are contained in an object calleda Mesh and the data values are contained in a Data object; a Field object contains the relationshipsthat bind the Mesh and Data objects together. Where the Mesh object contains simply a sequenceof locations related one-to-one to an array of values in the Data object, there is some similarity tothe Grid object of OPeNDAP, which contains exactly that: a sequence of locations and then the associatedvalues. The FSDM, however, elaborates upon the basic pattern in several ways.First, metadata are contained within (or closely associated with) both the Mesh object and the Dataobject, so the Field object is an entry point to more information about the data than just their valuesand points of origin. The Field object, along with the objects it binds, seems capable of providingthe information needed for “interoperability with semantic meaning.”Second, the Mesh object contains “cells,” which are spatial objects such as Points, Lines, and Hexahedrons.These cells include implementations of geometric “behavior” including facilities for forwardand reverse transformations through projections (e.g., Lambert Conformal-Conic) and definitionsof the coordinate systems (e.g., Polar).Third, there are issues currently under study of one-to-many and many-to-one relationships betweenData and Mesh components and of arbitrary, user-defined data types for Data values.A desired effect of the Field object having an abstract interface which hides internal data representationand storage is that there can be a consistent appearance to all geospatial data, regardless oflocal choices about physical data storage.Further study of this system, especially of FSDM, seems warranted, as it seems to embody a genuineattempt to conjoin geospatial data and metadata in (or beneath) one object and to present aconsistent view of geospatial data, such as will be required in the mature data transport system ofIOOS. The long-term utility of FSDM would likely be increased if it were to prove amenable toextension beyond solely the geospatial context to, for example, biologic, taxonomic, spectral, andfinite element modeling contexts.177