How does the Generic Delta Works

Question

Hi All,
Please let me know how the different types of Generic Delta works i.e. Numeric Pointer, 0Calday and Timestamp with one simple example for each.
Thanks & Regards,
Sunny

Answer 1

Hi........
There are three options for the type of the field determining the delta in a DataSource:
1. Time stamp - The field is a DEC15 field which always contains the time stamp of the last change to a record in the local time format.
2. Calendar day - The field is a DATS8 field which always contains the day of the last change.
3. Numerical pointer - The field contains another numerical pointer that appears with each new record.
Safety Interval Upper Limit of Delta Selection
This field is used by DataSources that determine their delta generically using a repetitively-increasing field in the extract structure.
The field contains the discrepancy between the current maximum when the delta or delta init extraction took place and the data that has actually been read.
Leaving the value blank increases the risk that the system could not extract records arising during extraction.
Example: A time stamp is used to determine the delta. The time stamp that was last read is 12:00:00. The next delta extraction begins at 12:30:00. In this case, the selection interval is 12:00:00 to 12:30:00. At the end of extraction, the pointer is set to 12:30:00.
A record - for example, a document- is created at 12:25 but not saved until 12:35. It is not contained in the extracted data but, because of its time stamp, is not extracted the next time either.
For this reason, the safety margin between read and transferred data must always be larger than the maximum length of time that it takes to create a record for this DataSource (with a time stamp delta), or it must display an interval that is sufficiently large (for determining delta using a serial number).
Safety Interval Lower Limit
This field contains the value taken from the highest value of the previous delta extraction to determine the lowest value of the time stamp for the next delta extraction.
For example: A time stamp is used to determine a delta. The extracted data is master data: The system only transfers after-images that overwrite the status in the BW. Therefore, a record can be extracted into the BW for such data without any problems.
Taking this into account, the current time stamp can always be used as the upper limit when extracting: The lower limit of the next extraction is not seamlessly joined to the upper limit of the last extraction. Instead, its value is the same as this upper limit minus a safety margin. This safety margin needs to be big enough to contain all values in the extraction which already had a time stamp when the last extraction was carried out but which were not read. Not surprisingly, records can be transferred twice. However, for the reasons above, this is unavoidable.
Extracted Data Delta Type
The system uses the delta type to determine how extracted data is to be interpreted in BW, and into which data targets it can be posted.
A distinction is made between the following:
1. Additive delta
The key figures for extracted data are added up in BW. DataSources with this delta type can supply data to ODS objects and InfoCubes.
2. New status for changed records
Each record to be loaded delivers the new status for the key figures and characteristics. DataSources with this delta type can write to ODS objects or master data tables.
Check this link :
http://help.sap.com/saphelp_nw2004s/helpdata/en/37/4f3ca8b672a34082ab3085d3c22145/content.htm
generic delta
Hope this helps you..........
Regards,
Debjani.............