BW Archiving in 3.0 is the process of selectively writing the data of a data target to a file and subsequently deleting this data from the respective data target. This process is split in two parts, one job for writing and one job for deleting the data. Hence, the consistency of the archived data is guaranteed. No data will be deleted before not all archive files of the write job are verified, that is, they are accessible and complete.
Archiving in BW uses the Archiving Development Kit (ADK). The ADK is well established in the R/3 environment. It has several beneficial features. Some of the BW relevant features of ADK are:

• Handling structural changes Since the ADK is storing metadata of the archived data as well as the data itself, it is capable of retrieving the archived data even after structural changes have been made. This data is not converted to the new structure, but simply displayed in the new structure.
• Platform independency The ADK can handle different code pages (ASCII, EBCDIC, UNICODE) and number formats.
• Data compression The archived data can be compressed up to 5 times of the original data volume.
• Archiving Information System (SAP-AS) The archived data can be displayed with the Archiving Information System. In BW, the customer has to define the InfoStructures for the respective archiving objects, and fill them manually within AS customizing.
• Administration via transaction SARA The scheduling, monitoring and management of the archiving session can be performed with the standard transaction SARA.

Read More about this in this PDF on How to Archieving in BW(PDF).