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 table key (primary key integrity), but many tables 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 key. A combination of fields in a table is known as a foreign key if it is also the primary key in another table.
In an ABAP-based SAP system, the data model is managed in the
ABAP Dictionary, which results in a close compliance with the ABAP type concept.
All the data relevant for all applications of an ABAP-based SAP NetWeaver Application Server is collected and managed centrally in a relational database. All ABAP application programs work with this data. The largely standardized language SQL can be used to access relational databases. SAP NetWeaver Application Server ABAP supports database systems from different vendors. SQL is embedded in the ABAP language either with standardized Open SQL or vendor-specific Native SQL.