.
Optional Rules are not part of the eAIP Specification; they are only recommendation.
3.3.2.1.2. Why additional rules?
The eAIP "language" is composed of a vocabulary (elements, attributes, lists of values), which is entirely defined in the DTD, and a grammar, which is split between the DTD and the addi-tional rules. This grammar split is due to limitations of the DTD technology, which does not allow to express all the grammar rules needed. As many constraints as technically possible have been put in DTD. In future, it might be decided to replace the DTD with an XML Schema. Even than, some additional rules might be needed, due to the inherent limitations of any schema language.
3.3.2.1.3. Implementation
The eAIP Specification defines the additional rules in plain English. An implementation of these rules, in Schematron language, is provided in the eAIP package, in the file ../../tools/Validator/eAIP-schematron.xml, which is located in the tools/Validator directory in the eAIP package. Schematron is another XML grammar language, like DTD and XML Schema. It is undergoing ISO standardization to become "ISO/IEC 19757 - DSDL Document Schema Definition Language - Part 3: Rule-based validation - Schematron". A Schematron grammar is written in XML and is able to express certain rules that DTDs and XML Schemas can't. For more information about Schematron, please refer to the Schematron home page [http://www.ascc.net/xml/resource/schematron/].
3.3.2.2. Mandatory Rules
3.3.2.2.1. Data Structure Rules
Route track Route segments within the same route may not have mixed true track and magnetic track.
Route sequence A Route sequence of Significant-point-reference and Route-segment elements must begin and end with a Significant-point-reference
Route-segment The first non-deleted element following a non-deleted Route-segment must be a Signific-ant-point-reference. The same assertion may be made about non-inserted ones, but we should expect the eAIP to be valid before the amendment anyway.
Significant-point-reference The first (if any) non-deleted element following a non-deleted Significant-point-reference must be a Route-segment. The same assertion may be made about non-inserted ones, but we should expect the eAIP to be valid before the amendment anyway.
Graphic-files If there are 2 Graphic-file elements inside a Figure element, their Updated attribute must be Inserted for one and Deleted for the other one.
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