What is a check table and What is a value table?

The relational data model contains not only tables, but also relationships between tables.
These relationships are defined in the ABAP/4 Dictionary by foreign keys. An important
function of foreign keys is to support data integrity in the relational data model. Foreign
key fields may assume only those values allowed by the check table, in other words,
values occurring in the primary key of the check table.
A foreign key provides a link between two tables, for eg.,T1 and T2 by including a
reference in table T1 to the primary key of table T2. For this purpose, Foreign key fields
assigned to the primary key fields of T2 are included in T1. Table T1, which is the one

being checked, is called a foreign key table, and table T2 is called a check table. The
terms dependent (foreign key) table and referenced (check) table are also used.

VALUE TABLE:If the domain of the check field has a value table, this is proposed by the system as check table in the foreign field maintenance. The key fields of the value table are in this case assigned fields of the foreign key table with the same domain. These
fields may assume only those values allowed by the value table.
The value range of the domain can be defined by specifying value table.All table fields
referring to this domain can then be checked against the corresponding field of this value
table.In order the check can be executed, a foreign key must be defined for the value
table.