Tables and Structures can be expanded in Two ways:
1. Append Structures:
2. Customizing includes
1. Append structures
Append structures are used for enhancements that are not included in the standard. This includes special developments, country versions and adding customer fields to any tables or structures.
An append structure is a structure that is assigned to exactly one table or structure. There can be more than one append structure for a table or structure.
The following enhancements can be made to a table or structure TAB with an append structure:
· Insert new fields in TAB,
· Define foreign keys for fields of TAB that already exist,
· Attach search helps to fields of TAB that already exist,
These enhancements are part of the append structure, i.e. they must always be changed and transported with the append structure.
Include Structure ->In addition to listing the individual fields, we can also include the fields of another structure in tables and structures. Individual fields and includes can be mixed as required.
When an include is changed, all the tables and structures that include it are automatically adjusted.
Includes can also be nested, that is structure A includes structure B which in turn includes another structure C, etc. The maximum nesting depth is limited to nine. The maximum length of a path of nested includes in a table or structure is therefore nine (the table/structure itself not included).
Check this SAP help
on append structure and Include Structure
http://help.sap.com/saphelp_nw04/helpdata/en/cf/21eb54446011d189700000e8322d00/frameset.htmDifference Between them
http://sap.ittoolbox.com/groups/technical-functional/sap-r3-bw/append-structure-vs-include-structure...2. Customizing includes:A Customizing include is a structure that satisfies a special naming convention. The name of a Customizing include begins with ‘CI_’ and the include is in the customer namespace.
If enhancements are already planned in the standard using customer-specific fields, such Customizing includes are included. in the corresponding standard table or standard structure. The Customizing include (that is the definition of the structure itself) is usually first created in the customer system and filled with fields by special Customizing transactions.
Customers can thus enhance tables and structures of the standard system without themselves having to modify the table and structure definitions. This means that these enhancements will not be lost when upgrading. If a table or structure of the standard system is enhanced with customer fields using a Customizing include, these customer fields are automatically inserted in the new delivered table or structure definition during an upgrade.
If you create a Customizing include for a table or structure, only those enhancements are allowed that are consistent with the enhancement category of the enhanced table or structure. For more information, see Structure Enhancements.
Customers can but need not create a Customizing include and fill it with fields. If there is no Customizing include, there is no error message when the table or structure including it is activated.
A Customizing include can be contained in several tables or structures, so that they remain consistent when the include is modified.
Best Regards,
Raj
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Bluesky
