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Encoding: GML Vs ISO-19118



It seems that OpenGIS and ISO recognised the importance of providing the Geo-Information Community with interoperable encoding languages (XML-enabled). In particular, they decided to make GML more compliant with ISO 1900 standards, and ISO 19118, specifically.

I quote an important adopted resolution:
" ISO/TC 211 Resolution 191: Harmonization of ISO 19100-series and Geography Markup Language (GML)

ISO/TC 211 recognizes the need for harmonization between the ISO 19100-series and GML, and specifically between ISO 19118 Encoding and GML. To ensure harmonization, ISO/TC 211 instructs the secretariat in cooperation with the CD 19118 editing committee chair to make the necessary changes to ISO 19118 Encoding and send it and a change report out for a new review together with the revised NWIP for GML.

ISO/TC 211 welcomes the proposal from Open GIS Consortium (OGC) and Germany for Mr. Clemens Portele as project leader for the NWIP. "





What does "harmonization" mean? According to the same resolution:
" ISO 19118 defines XML Encoding Rules for conceptual models described in UML and following the rules of ISO 19103 (ISO 19107, ISO 19108, ISO 19111, ISO 19112 and ISO 19115) and ISO 19109 (application schemas). The rules allow for a range of encoding choices, therefore, there is no single XML representation for an UML model and therefore no standard encoding of the harmonized ISO 19100 model.

On the other hand, GML defines a fixed XML Schema and defines rules for the XML Schema encoding of application schemas.

After a successful harmonization with ISO 19100 GML can be derived by applying the ISO XML Encoding Rules to an ISO 19100 conformant profile (plus additional 19103 conformant UML models for aspects that are part of GML but not of ISO 19100). This includes that ISO 19109 conformant application schemas must translate to GML application schemas.

In other words: GML fits into the ISO 19100 series.

Note that at least two ways to produce GML applications schemas must be supported. One is the model driven approach of ISO 19100 (UML model  XML Schema definition). At the same time it must be still valid to ?handcraft? GML application schemas (these may not be conformant to ISO 19100, but will still be valid GML application schemas). "



In my opinion, that is a good piece of news: it is an important step towards disparate system interoperability; it is a positive answer to the heterogeneity issue of the encoding standards, we discussed during my seminar.


---Stefano Nativi




Dr. Stefano Nativi (Professor with no-track position)
University of Florence - Polo di Prato
P.za Ciardi, 25 - 59100 Prato (ITALY)


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