Glossary A–ZLetter X
XML
XML is a text-based markup language in which data is described hierarchically using self-named elements in angle brackets, so that both people and programs can read it.
The abbreviation stands for “Extensible Markup Language”; the language is a W3C standard.
Many formats in the signage world are based on XML: the SMIL playlist is XML, as are RSS feeds, SVG graphics and the structured invoice data in ZUGFeRD. Older interfaces of merchandise management systems, journey planners or weather services also often supply their data as XML. A schema can be defined for XML documents, against which a program checks whether all mandatory details are present and correctly structured.
XML is more verbose than JSON and therefore larger, but it is well suited to documents with fixed rules. Operators rarely need to write XML themselves, but should know that a single missing closing element makes an entire file unreadable. The character encoding is important: umlauts and special characters must be saved in the declared encoding. When reading XML from external sources, the parsing software needs secure settings.