The FREE Universal Interface
What does "well-formed” mean?
Without exception, all XML documents must be well-formed. This means that they must follow a set of rules, including these:
• Each start tag must have an associated end tag.
• Elements may be nested, but must not overlap.
• There must be exactly one root element.
• Attribute values must be in quotation marks.
• An element must not have two attributes with the same name.
• Comments and processing instructions must not be within tags.
• The character data of an element or attribute must not contain any unprotected < or & signs.
• A complete list can be found here: https://www.data2type.de/xml-xslt-xslfo/xml/xml-in-a-nutshell/xml-referenz/einschraenkungen/
What does "validity" mean?
Validity means that the present XML document:
• is well-formed
• complies with the rules of the applied XSD (XML Schema Definition)
How can I validate the XML file?
The validation of XML files is done in 2 steps:
1.) Syntax check for "well-formedness". In this step the XML file's
validity will be checked by tools such as the Altova XML-Spy without schema.
2.) "Schema conformity" check: The XML file is checked against the schema. This is also possible with the help of tools like Altova XML-Spy.
In the XML-Spy, a project with the schema should be created. To check the XML file, it is advisable to also include it in the
project. For the two test steps there are the functions "check well-formedness" and "validate file" available.
XML Schema, abbreviated XSD (XML Schema Definition) - what is that?
An XML schema defines the structures for XML documents. An XSD defines the rules for an XML document, so to speak. This is useful if a large number of data records are to be tested for correctness prior to processing by an XML processor, regardless of the type.
The XSD file usually has the extension .xsd and describes data types, individual XML schema instances (documents) and groups of such instances.
With the XSD XML documents can be checked for correctness (validity). Validation can detect errors in an XML document before importing the data into a program.
Advantages of XML
• XML files contain only text, never binary data and can therefore be opened with any program (text editor) that can process texts.
• No special licenses required for programs, even the file format itself is license-free.
• Format neutral. How tags are formatted by the evaluating program is a matter of the styles applied or the XSL (eXtensible Stylesheet Language) applied.
• XML is easy to learn compared to other metalanguages.
• Open standard, which is well documented.
• Can be used across programs - there are countless programs that can be used to process XML.
• "Industry standard" for format-neutral data exchange between any systems.
• Can be easily validated to ensure later trouble-free processing.