SAP ALE Distribution Scenario

ALE is a simple add-on application based on the IDoc concept of SAP R/3. It consists of a couple of predefined ABAPs which rely on the customisable distribution scenario. These scenarios simply define the IDoc types and the pairs of partners which exchange data.

ALE defines the logic and the triggering events which describe how and when IDocs are exchanged between the systems. If the ALEE engine has determined which data to distribute, it will call an appropriate routine to create an IDoc. The actual istribution is then performed by the IDoc layer.

The predefined distribution ABAPs can be used as templates for own development ALE uses IDocs to transmit data between systems.

ALE is, of course, not restricted to the data types which are already predefined in
the BALE transaction. You can write your ALE distribution handlers which should
only comply with some formal standards, e.g., not bypassing the ALE scenarios.

All ALE distribution uses IDocs to replicate the data to the target system. The ALE
applications check with the distribution scenario and do nothing more than call the
matching IDoc function module, which is alone responsible for gathering the
requested data and bringing them to the required data port. You need to thoroughly
understand the IDoc concept of SAP beforehand, in order to understand ALE.

The process is extremely simple: Every time a data object, which is mentioned in an
ALE scenario changes, an IDoc is triggered from one of the defined triggering
mechanisms. These are usually an ABAP or a technical workflow event.

Distribution ABAPs are started manually or can be set up as a triggered or timed
batch job. Sample ABAPs for ALE distribution are those used for master data
distribution in transaction BALE, like the ones behind the transaction BD10, BD12
etc.

The workflow for ALE is based on change pointers. Change pointers are entries in a
special database entity, which record the creation or modification of a database
object. These change pointers are very much like the SAP change documents. They
are also written from within a change document, i.e. from the function
CHANGEDOCUMENT_CLOSE. The workflow is also triggered from within this
function.

SAP writes those ALE change pointers to circumvent a major draw back of the
change documents. Change documents are only written if a value of a table column
changes, if this column is associated with a data element which is marked as
relevant for change documents (see SE11). ALE change pointers use a customised
table which contains the names of those table fields which are relevant for change
pointers.