ARTICLE
Logical Databases - Components
A logical database is a special development object that is edited in
Logical Database Builder and which provides
other ABAP programs with data from the nodes of a hierarchical tree
structure. The most common purpose of logical databases is to extract
data from database tables, however other applications are feasible.
Logical databases provide a hierarchical view across database tables
associated using foreign key relationships. If parts of these r
elationships construct tree-like hierarchical structures, logical
databases can read data from database tables that are components of
these structures. In classic ABAP, logical databases are usually used in
these hierarchical structures in accordance with the principle of
input, processing, and output . The actual database reads are then
wrapped in the logical database. The logical database reads the data,
saves it locally in the program (if necessary) and passes it row by row
to an interface work area .
As well as reusing predefined functions for reading data from database
tables, logical databases can be implemented for further central tasks,
such as defining uniform selection screens, central authorization
checks, or making centralized enhancements to performance.
The main features of a logical database are
a hierarchical structure
The structure defines the data view of the logical database. It
generally inherits the given hierarchy of database tables defined by
foreign key relationships and controls the order in which the data is
passed to the application program. In this way, the structure determines
how the other subobjects are constructed and the runtime behavior.
selections as a standalone standard selection
screen
The selections define a standard selection screen to be used as a user
interface for programs that use the logical database. The appearance of
the screen is defined by the structure by default. The selections can be
modified and enhanced to meet the requirements of the user.
a database program written in ABAP
The database program contains the ABAP statements for reading the data
and passing it to an application program. It is basically a container
for special subroutines in which the functions of the logical database
are implemented. The reporting processor
of the runtime environment calls these subroutines in the order defined
by the structure. The database program is defined by the structure and
the selections and can be modified or enhanced to meet the requirements
of the user.
Further elements , which add to the functions.
When an executable program is created, it can be assigned to a logical
database using the Logical Database attribute. This allows the
standard selection screen and the program flow to be combined with the
selection screen and flow of the logical database.
Furthermore, logical databases can call the function module
LDB_PROCESS . This function module
can be used to call multiple logical database from a single program and
nested as required. A logical database can also be called more than once
in a program, if programmed accordingly.
Note
When creating a logical database in Logical Database
Builder , the following order should be kept, since this then makes
it easier to generate proposal for the remaining components from the tho
se already created. Some of the most important properties of a logical
database are defined at the same time as its structure. After the
definition of the structure, a proposal is created for the selection
include. The structure and selection include are used to generate a
template for the database program. These components can then quickly
be used to create a ready-to-run logical database, in which further req
uirements can be implemented.
Create the structure based on a root node.
Associate it with a search help.
Generate and edit the selection include.
Generate and edit the database program.
Edit further elements.
Documentation extract taken from SAP system, � Copyright SAP AG. All rights reserved