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AIXM 5.1 – use of CRC

AIXM 5.1 – use of CRC. Draft proposal. ADQ Context – pragmatic solution. Regulator group to acknowledge formally that CRC32 is not mandatory; more constraining algorithms (MD5, SHA-1, SHA-2, etc.) would be a sufficient means of compliance AIXM CRC Guidelines

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AIXM 5.1 – use of CRC

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  1. AIXM 5.1 – use of CRC Draft proposal

  2. ADQ Context – pragmatic solution • Regulator group to acknowledge formally that CRC32 is not mandatory; more constraining algorithms (MD5, SHA-1, SHA-2, etc.) would be a sufficient means of compliance • AIXM CRC Guidelines • Provide a ‘basic’ CRC solution (extension), for those who are imposed by their regulator to strictly comply with the Regulation ADQ CRC Workshop

  3. CRC - guidelines • operational principles • AIXM 5.1 support • extension Initial draft ADQ CRC Workshop

  4. The VERY IMPORTANT question • Do we need to allocate a CRC value when the data is originated and preserve (store/transmit) that same CRC value along the whole data chain, up to the end user? Or • Is it OK if CRC are used just for data in transit, meaning that they are calculated 'on the fly' when the data is packed for transmission, checked at the other end and then dropped? ADQ CRC Workshop

  5. CRC recalculation allowed when merging data sub-sets Data merging – re-calculate CRCV! ADQ CRC Workshop

  6. CRC in AIXM 5.1 • Nothing included in the core model • Unclear requirements at the time when model was finalised • Original thought – use Metadata (ISO 19139) schema, already embedded in AIXM 5.1 • Current proposal • AIXM 5.1 extension • Main principle = flexibility • CRC on whole features and/or selected attributes • Use xpath to indicate which elements are included ADQ CRC Workshop

  7. CRC Extension ADQ CRC Workshop

  8. CRC extension ADQ CRC Workshop

  9. AIXM 5.1 – resulting XML encoding • AIXM Extensions • Each AIXM Feature • CRC “subjects” - xPath expression … <crc:protectedData> <crc:DataBlock gml:id="ID_0002"> <crc:items>//aixm:ARP//gml:pos | //aixm:ARP//aixm:elevation | //aixm:ARP//aixm:elevation/@uom</crc:items> <crc:value>582C2727</crc:value> </crc:DataBlock> </crc:protectedData> … ADQ CRC Workshop

  10. CRC in AIXM 5.1 • Open questions • Need to specify CRC algorithm? • Probably not, also allow MD5, SHA-1, SHA-2, etc. • Doe we need a predefined list? • CRC calculated on values only? • Same CRC value remains valid during non-XML storage • Or also including tags? • Unusable for non-XML storage ADQ CRC Workshop

  11. Questions ADQ CRC Workshop

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