Application software models a part of the real world. This type of modeling is based on the relational
data model. A data model describes reality through formal structures. In the relational data
model, the only formal structure used is known as a relation or table. All the information
about the modeled area of reality is represented as values in tables.
A table is a two-dimensional
matrix which consists of lines and columns (fields).
The value range of a field, i.e. the set
of permitted values for the field, is also known as the domain of the field.
A
field or combination of fields which uniquely identifies every line in a table is known as the key.
This is a minimal attribute since, if one of the fields is removed from the key, the remaining fields
cannot uniquely identify the table entries.
Each table must have at least one key (primary
key integrity), but many tables often often have several keys. During the modeling process, one key
is defined as the primary key.
In the relational model, the relationship between
objects is expressed in terms of foreign keys. A combination of fields in a table is known as a foreign
key if it is also the primary key in another table.
In the R/3 System, the data model is managed in the ABAP/4 Dictionary.
The data required by all the applications is collected together and managed in a pool known as the relational
database. All the applications programs then address this database, normally by means of the
extensively standardized SQL (Structured Query Language). The R/3 System supports a
number of database systems. The embedding of SQL in the ABAP/4 language is achieved either with standardized
Open SQL statements or with
Native SQL in the language of the database system being used.
Siehe auch Database Accesses in the R/3 System