2.1. General
The EUROCONTROL eAIP is a specification for the publication and exchange of the Aeronautical Information Publication in electronic format.
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Specification: the eAIP defines an electronic format and the general usage process
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Publication: the eAIP is designed to be published, be it on screen or on paper and used by people;
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Exchange: to a certain extent, the eAIP can be used for computer-to-computer data ex-change. However, the eAIP Specification does not offer the same capabilities for structured aeronautical data exchange as the Aeronautical Information Exchange Model (AIXM).
The essential difference between the two is that AIXM models the aeronautical information, while the eAIP models the AIP document. AIXM is primarily intended for computer-to-computer aeronautical data exchange. The eAIP is primarily intended to provide the AIP content for publication in various formats and on various media, according to user needs.
2.2. Technology
The EUROCONTROL eAIP is based on XML (eXtensible Mark-up Language). An electronic AIP is in fact an XML document, conforming to the eAIP DTD.
The eAIP in XML is transformed into other formats using XSLT:
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for on-screen display, the eAIP is transformed into HTML (Hyper-Text Mark-up Lan-guage);
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when paper is the target, the eAIP is transformed into XSL-FO. Software tools must be used to print XSL-FO. Currently, the most convenient method is to first convert XSL-FO to PDF or PostScript and then print those files.
Charts and graphics can be in various formats, and a very interesting one for aeronautical charts is Scalable Vector Graphics (SVG). All these technologies are official recommendations (standards) published by the W3C (World Wide Web Consortium).
2.2.1. What is XML
XML stands for eXtensible Mark-up Language. XML is a subset of the Standard Generalized Markup Language (SGML, ISO 8879). Since 1998, when it was published as a recommend-ation by the World Wide Web Consortium (W3C), XML has rapidly become the de-facto industry standard for electronic data interchange.
XML is a meta-language (a language to define other languages). It allows us to define an "AIP language" for computers. Using the EUROCONTROL eAIP language, people and computers can talk to each other using the same vocabulary and grammar.
XML has been chosen because it fulfils the eAIP's main objective: it is commonly used for structuring documents and it is suitable for both human to computer and computer to computer interactions. Also, it is a recognised standard since 1998, widely adopted by the software developers in many industries.
2.2.2. What is a DTD
DTD stands for Document Type Definition. It is a formal representation of XML documents' structure. To keep up with our previous analogy with languages, the eAIP DTD is a formal definition of the eAIP language vocabulary and grammar.
2.2.3. What is XSLT
XSLT stands for eXtensible Stylesheet Language Transformations. It is an XML-based lan-guage that allows to transform an XML document into another XML document (or into text document as well). In the eAIP context, XSLT is used to convert eAIP files from XML into HTML format or XSL-FO format.
2.2.4. What is XSL-FO
XSL-FO stands for eXtensible Stylesheet Language Formatting Objects. It is an XML-based language that allows to express a document with its formatting, for example to print it on paper. In the eAIP context, XSL-FO is used to format an eAIP in order to print it on paper. With adequate software, it will be possible in future to directly print an XSL-FO document. In the mean time, it is possible to use software that convert XSL-FO to PDF or PostScript and then print those files.
2.2.5. What is SVG
SVG stands for Scalable Vector Graphics. It is an XML-based language to express 2-dimen-sional drawings using simple graphical objects such as lines, circles, rectangles and text, and object properties such as color, size and position. Being written in XML, SVG charts can quite easily be linked to other XML information.
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