Dev:Syntactic Guidelines
Newly created files
Byte order mark (BOM)
For more information about the "Byte Order Mark" see Wikipedia: Byte Order Mark (BOM) (external link)
As recommended by the W3C, an UTF-8 encoded file should not start with an BOM for less troubles with editors and browsers, see also W3C Recommandation about BOM
Visualization tip for BOM (command line tool): less $FILENAME$
<U+FEFF><?xml version="1.0" encoding="UTF-8"?>
Camel Case
Always use camel case for all names. Don't mix with dashed naming schemas.
White spaces
Empty end-tags
Implementation with 1 space before closing empty end-tags
example:
<xs:restriction base="xs:ID" />
Indents
Implementation with 2 spaces
example:
<xs:element name="railml"> <xs:complexType> <xs:sequence> <xs:element name="metadata" type="dc:elementContainer" minOccurs="0" /> <xs:element ref="rail:infrastructure" minOccurs="0" />
Line Breaks
Each component declaration must be followed by a line break.
example:
<xs:attributeGroup name="aPlaces"> <xs:attribute name="category" type="rail:tPlaceCategory" use="required" /> <xs:attribute name="count" type="rail:tCounter" use="required" />
There is no maximum line length
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Each component has to be fully declared on one line without line breaks.
example:
<xs:schema xmlns:rail="https://www.railml.org/schemas/2009" xmlns:xs="https://www.w3.org/2001/XMLSchema" xmlns:dc="https://purl.org/dc/elements/1.1/" targetNamespace="https://www.railml.org/schemas/2009" elementFormDefault="qualified" version="2.0">
XML Default Values
Empty elements and attributes
see also: W3C XML Recommendation "Tags for Empty Elements"
Implementation with shortened syntax instead of extra closing tag
example:
<xs:element ref="rail:infrastructure" minOccurs="0" />
XML Schema Default Values
Optional and required attributes
see also: W3C XML Schema Recommendation "XML Representation of Attribute Declaration Schema Components"
Implementation without use="optional"
example:
<xs:attribute name="description" type="rail:tElementDescription" />
Implementation with use="required"
example:
<xs:attribute name="id" type="rail:tGenericID" use="required" />
Elements with minimum 1 or maximum 1 occurrence
see also: W3C XML Schema Recommendation "XML Representation of Element Declaration Schema Components"
Implementation without minOccurs="1"
example:
<xs:element name="train" type="rail:eTrain" maxOccurs="unbounded" />
Implementation without maxOccurs="1"
example:
<xs:element ref="rail:timetable" minOccurs="0" />
Occurence restrictions into elements
If possible, all occurence restrictions have to go into element definitions.
xs:sequence
should stand without the attributes minOccurs
and/or maxOccurs
.
example:
<xs:extension base="rail:tElementWithIDAndName"> <xs:sequence> <xs:element name="metadata" type="dc:elementContainer" minOccurs="0" /> </xs:sequence>
Pathes inside XML documents
Attribute xsi:schemaLocation
see also: W3C XML Schema Recommendation "How schema definitions are located on the Web"
Implementation with slashes, no backslashes permitted
example:
<railml xmlns="https://www.railml.org/schemas/2009" xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="https://www.railml.org/schemas/2009 ../schema/railML.xsd">