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
- " 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
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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