With the exception of the purpose-designed GS1 DataBar family of barcodes the remaining GS1 barcode symbologies are "application standards" of various general-purpose ISO/IEC barcode standards adapted for dedicated use within the supply chain industry and are specified by the GS1 General Specifications. Each format was created as a specialisation of some pre-existing carrier symbology (Code 128, Data Matrix, QR Code), meaning that they work within the limits of the existing specification to produce a more-restricted, special-purpose variant that is optimised for use in their particular application – for example by reducing the range of available symbol sizes, applying constraints on the data capacity and specifying a particular structure for the encapsulated data.
With regard to having a mandatory data structure, where available in the carrier symbology the GS1 specialisations mandate the use the "FNC1 in first position" mechanism to indicate the presence of data that conforms to the GS1 Application Identifier standard format described by the GS1 specifications. The product data is thus represented within this standard format and encoded within the carrier symbol using a scheme that is broadly similar across the GS1 symbologies.
The "extraction" part of this answer gives details of formatting data according to the GS1 AI standard format structure.