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Delta Transfer into BW 
The following update modes are available in the Business Information Warehouse scheduler:
● Full update
A full update requests all data that meet the selection criteria you set in the scheduler.
● Delta update
A delta update only requests data that has appeared in the source system since the last load.
● Initializing the delta process
You need to initialize a delta process before it can work. The initialization selections are taken for the loading of delta records.
With large data volumes, a performance-optimized extraction from the source system is only feasible using a delta process.
In the maintenance of the generic DataSource, you can set up a delta for master data attributes and texts. You can also set up a generic delta using a (delta-relevant) field with a value increasing monotonously.
Master data attributes or texts for which the delta transfer is to be used must meet two prerequisites:
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1. Data must be extracted generically using a transparent table or a database view.
2. A change document object must be available that is able to update the complete key for table used in the data extraction (or the table for the view) in combination with one of the tables based on the change document object.
The required control entries are delivered for the most important master data attributes or texts. By including a maintenance interface for control entries in the maintenance of generic DataSources/InfoSources, you can use the delta transfer for other master data attributes or texts.
To generate the control entry for master data attributes/texts necessary for BW, proceed as follows:
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1. For an attribute or text DataSource, choose DataSource ® ALE Delta.
2. Enter the table and the change document object that you want to use as a basis for the delta transfer.
An intelligent F4 help for the Table Name field searches all possible tables for a suitable key.
3. Confirm your entries.
With a usable combination of table and change document object, the extraction structure fields are listed in the table below. The status in the first column displays whether a field leads to a transfer of the delta record when master data is changed in this field.
4. Save the settings to generate the required control entry.
Delta transfer is now possible for master data/texts.
After the DataSource has been generated, you can see this from the selection of the Delta Update field in the screen DataSource: Edit Customer Version.

You need two separate entries if you want to transfer delta records for texts and master data attributes.
If a field exists in the extraction structure of a DataSource that contains values which increase monotonously over time, you can define delta capability for this DataSource. If such a delta-relevant field exists in the extraction structure, for example a timestamp, the system determines the data volume transferred in the delta mode by comparing the maximum value transferred with the last load with the amount of data that has since entered the system. Only the data that has newly arrived is transferred.
To get the delta, generic delta management translates the update mode into a selection criterion. The selections of the request are enhanced with an interval for the delta-relevant field. The lower limit of the interval is known from the previous extraction. The upper limit is taken from the current value, for example the timestamp at the time of extraction. You can use security intervals to ensure that all data is taken into account during extractions (see below). After the data request was transferred to the extractor and the data was extracted, the extractor then informs generic delta management that the pointer can be set to the upper limit of the previously determined interval.

The delta for generic DataSources cannot be used with a BW system release prior to 3.0. In older SAP BW releases, the system does not replicate DataSources for master data and texts that were delta-enabled using the delta for generic DataSources.
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1. Choose Generic Delta.
2. In the subsequent dialog box, specify the delta-determining field and the type for this field.
3. Maintain the settings for the generic delta:
a. Enter a security interval.
The purpose of a security interval is to make the system take records into account that appear during the extraction process but which could not be extracted (because, for example, they have not been saved) during the next extraction.
You have the option of adding a security interval to the upper limit/lower limit of the interval.

A security interval should only be specified for the lower limit when the delta process results in a new status for changed records (when the status is overwritten in BW). In this case, duplicate data records that could arise in such a security interval have no affect on BW.
b. Choose the delta type for the data to be extracted.
You use the delta type to determine how the extracted data is interpreted in BW and into which data targets it can be updated.
With the Additive Delta delta type, the record to be loaded for summarizable key figures only returns the change to the respective key figure. The extracted data is added in BW. DataSources with this delta type can supply ODS objects and InfoCubes with data.
With the delta type New Status for Changed Records, every record to be loaded returns the new status for all key figures and characteristics. The values in BW are overwritten. DataSources with this delta type can write the data into ODS objects and master data tables.
c. Determine whether the DataSource supports real-time data acquisition.
4. Save your entries.
Delta transfer is now possible for this DataSource.
After generating the DataSource, you can see this from the selection of the Delta Update field on the DataSource: Customer Version screen.

In systems from Basis Release 4.0B, you can display the current value of the delta-relevant field in the delta queue.
Security interval upper limit
The delta-relevant field is a timestamp.
The timestamp that was read last is 12:00:00. Delta extraction begins at 12:30:00. The security interval for the upper limit is 120 seconds. The selection interval for the delta request is: 12:00:00 to 12:28:00. Upon completion of the extraction, the pointer is set to 12:28:00.
Security interval lower limit
The delta-relevant field is a timestamp. After images are transferred. That is, in BW the record is overwritten with the status after the change, for example for master data. Any data records that are transferred twice do not effect BW.
The last read timestamp is 12:28:00. Delta extraction begins at 13:00. The security interval for the lower limit is 180 seconds. The selection interval for the delta request is: 12:25:00 to 13:00:00. Upon completion of the extraction, the pointer is set to 13:00:00.