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TYPO3 offers an XML format, T3DataStructure, which defines a hierarchical data structure. In itself the data structure definition doesn't do much - it is only a back bone for higher level applications which can add their own configuration inside.
Such applications can be:
FlexForms - a TCEform type which will allow users to build information hierarchies (in XML) according to the Data Structure. In this sense the Data Structure is like a DTD (Document Type Definition) for the backend which can render a dynamic form based on the Data Structure;
TemplaVoila! - an extension which uses the Data Structure as backbone for mapping template HTML to data.
This documentation of a data structure will document the general aspects of the XML format and leave the details about FlexForms and TemplaVoila to be documented elsewhere.
Some other facts about Data Structures (DS):
A Data Structure is defined in XML with the document tag named "<T3DataStructure>"
The XML format generally complies with what can be converted into a PHP array by
\TYPO3\CMS\Core\Utility\GeneralUtility::xml2array()- thus it directly reflects how a multidimensional PHP array is constructed.
A Data Structure can be arranged in a set of "sheets". The purpose of sheets will depend on the application. Basically sheets are like a one-dimensional internal categorization of Data Structures.
Parsing a Data Structure into a PHP array is incredibly easy - just pass it to
\TYPO3\CMS\Core\Utility\GeneralUtility::xml2array()(see the Parsing a Data Structure section).
"DS" is sometimes used as short for Data Structure