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Archiving Format for Packed ResourcesLocate this document in the navigation structure

Use

If resources for one collection are packed in XML DAS data archiving, a new physical file arises from the physical files in the same collection or in the same file system directory. It receives the suffix .axml (for "Archive XML"). SAP deliberately leaves the format of .axml files open to ensure future-proof, compact storage of the contents of a collection. With the following description it is always possible to read or reconstruct packed resources with other tools.

The archiving format defined by SAP is based on the following principles:

  • Standard orientation (use of widely-used standardized compression, taking into account XML)

  • Simplicity (inclusion of meta data essential for long-term archiving, enablement of easy implementation of interpreters for .axml files by sequential block structure with length specification)

  • Error tolerance, (high probability for finding restart points in case of corrupt blocks, platform-independent specification)

  • Efficiency (byte addressable for direct access)

An .axml file consists of a header and a series of blocks. Each block begins with a prefix and then contains a compressed resource. This structure is illustrated in the following figure.

The exact structure of the header is represented in the following figure. All text metadata is UTF-8 coded. Included in this are the fixed initial ID "AXML" and the release description "01.0". Similar to the use in the GZIP format (RFC 1952) and in the ZLIB format (RFC 1950) only the "Deflate" compression algorithm from RFC 1951 is supported, and consequently the 5 byte set as X'08'. AXML are not encrypted by XML DAS in format release 1.0, so that the 6 byte here is X'00'. The length of the URI for the AXML file is written in front of the URI itself. The most significant bytes of the length code precede the least significant.

As the following figure shows, each prefix begins with the MIB number for the unicode transformation UTF-8 used, in accordance with the IANA (Internet Assigned Numbers Authority) standard for character sets. The XML DAS type of the resource follows in UTF-8, for example, X'58 4D 4C' for "XML". 1 byte is necessary for the length specification of the resource name, while 4 bytes are reserved for the length of the compressed resource. Similar to the header, the most significant bytes are stored first irrespective of the platform.