Semantic key in Write optimized DSO

Understanding Write-Optimized DataStore keys:
 
Since data is written into Write-optimized DataStore active-table directly, you may not need to activate the request as is necessary with the standard DataStore object. The loaded data is not aggregated; the history of the data is retained at request level. . If two data records with the same logical key are extracted from the source, both records are saved in the DataStore object. The record mode responsible for aggregation remains, however, the aggregation of data can take place later in standard DataStore objects.
 
The system generates a unique technical key for the write-optimized DataStore object. The technical key consists of the Request GUID field (0REQUEST), the Data Package field (0DATAPAKID) and the Data Record Number field (0RECORD). Only new data records are loaded to this key.
 
The standard key fields are not necessary with this type of DataStore object. Also you can define Write-Optimized DataStore without standard key. If standard key fields exist anyway, they are called semantic keys so that they can be distinguished from the technical key.
 
Semantic Keys can be defined as standard keys in further target Data Store. The purpose of the semantic key is to identify error in the incoming records or duplicate records. All subsequent data records with same key are written to error stack along with the incorrect data records. These are not updated to data targets; these are updated to error stack. A maximum of 16 key fields and 749 data fields are permitted. Semantic Keys protect the data quality. Semantic keys wonu2019t appear in database level. In order to process error records or duplicate records, you must have to define Semantic group in DTP (data transfer process) that is used to define a key for evaluation. If you assume that there are no incoming duplicates or error records, there is no need to define semantic group, itu2019s not mandatory.
 
 
The semantic key determines which records should be detained when processing. For example, if you define "order number" and u201Citemu201D as the key, if you have one erroneous record with an order number 123456 item 7, then any other records received in that same request or subsequent requests with order number 123456 item 7 will also be detained. This is applicable for duplicate records as well.
 
 
Semantic key definition integrates the write-optimized DataStore and the error stack through the semantic group in DTP.  With SAP NetWeaver 2004s BI SPS10, the write-optimized DataStore object is fully connected to the DTP error stack function.
If you want to use write-optimized DataStore object in BEx queries, it is recommend that you define semantic key and that you run a check to ensure that the data is unique. In this case, the write-optimized DataStore object behaves like a standard DataStore object. If the DataStore object does not have these properties, unexpected results may be produced when the data is aggregated in the query.