A 121-page document Recommended Definition Data for Coordinate Reference Systems and Coordinate Transformations has been made available for public review by the Open GIS Consortium. The recommendation paper provides a data model which "harmonizes and improves the relevant XML work previously done by OGC. This OGC standard data model for coordinate reference systems and coordinate transformation definition data is intended for initial use with OGC's OpenGIS Geography Markup Language (GML) and Coordinate Transformation (CT) Implementation Specifications. That is, each of these two specifications is expected to use a subset and/or superset of the Definition Data described in the Recommendation Paper. The data model was developed using object-oriented analysis and design principles and is recorded in XML format. Future revisions of this specification will convert the current XML Document Type Definitions (DTD) to XML Schema." Section 6 supplies the normative XML data model; Annex D provides the uncommented XML DTDs; Annex E offers XML examples; Informative Annex G documents correspondences between the XML DTD and UML. OGC is "an international industry consortium of over 200 companies, government agencies and universities participating in a consensus process to develop publicly available geoprocessing specifications."

Bibliographic information: Recommended Definition Data for Coordinate Reference Systems and Coordinate Transformations. OpenGIS Recommendation Paper. Reference: OpenGIS Project Document 01-014r3. Version 1.0.1. File name: 01-014r3. 121 pages. By Arliss Whiteside (BAE SYSTEMS Mission Solutions), John Bobbitt (Petrotechnical Open Software Corporation), and Roel Nicolai (Shell International Exploration and Production).

From the recommendation:

The proposed OGC Recommendation Paper specifies OGC standard definition data for Coordinate Reference Systems (CRSs) and Coordinate Transformations (CTs). This proposal is intended for consideration by the Coordinate Transformation (CT) Working Group (WG). Those familiar with the format of OGC documents will notice that the attached paper uses a different format. This proposed Recommendation Paper uses the tentative new format for OGC Implementation Specifications that is similar to the ISO document format. This new format was developed by Martin Ford.

This Data Model is recorded in XML format for a combination of several reasons, including: (1) CRS and CT definition data will very often be transferred in XML format, so this data must be defined such that subsets can be effectively encoded in XML, in various Implementation Specifications. (2) Although XML cannot represent interface classes or class operations, this is not a problem for representing the Data Model, since no operations are allowed. (3) Many interested OGC participants find XML easier to understand than UML (often because they are more familiar with XML). If considered useful and worthwhile, a UML equivalent to this XML Data Model could be generated in a straight-forward manner. For example, the UML equivalent model might be generated by applying the correspondences described in Annex F.

This specification harmonizes and improves the relevant XML work previously done by the Open GIS Consortium (OGC). The OGC-accepted CT Implementation Specification already specifies a XML DTD for CRSs and CTs. The approved GML Recommendation Paper now includes an informative annex that specifies a XML DTD for CRSs, including some CTs. These two XML DTDs are significantly different, and both appear to be incomplete. Use of an OGC standard for CRS and CT definition data is believed needed when the current GML Recommendation Paper is converted to an Implementation Specification. This OGC standard data model for CRS and CT definition data is intended for initial use by the Geography Markup Language (GML) and in Coordinate Transformation (CT) Implementation Specifications. That is, each of these specifications is expected to use a subset and/or superset of the OGC standard definition data. In future revisions of this specification, the current XML DTDs will be converted to XML Schema. Many of the geospatial concepts used in this specification are from ISO DIS 19111 and Topic volume 2 of the OGC Abstract Specification (OGC document 01-102). However, whereas ISO DIS 19111 distinguishes between two types of Coordinate Operation, viz. Coordinate Conversion and Coordinate Transformation, this document, although implementing these concepts materially, refers to both collectively as 'Coordinate Transformation', thereby not using the term 'Coordinate Operation'.