Field symbols are placeholders or symbolic names for other fields. They do not physically reserve space for a field, but point to its contents. A field symbol can point to any data object. The data object to which a field symbol points is assigned to it after it has been declared in the program.
Whenever you address a field symbol in a program, you are addressing the field that is assigned to the field symbol.
Field-symbols can increase performance to work with internal tables. If you use u2018ASSIGNINGu2019 command instead of u2018INTOu2019 SAP wonu2019t have the cost of copying current table row into work area.so it wil increase ur performance...
We can say FIELD STRING is also an work area, but in field string we can have our fields defined i.e. we can restrict number of fields here.
Eg. Begin of fs (occurs 0/with header line),
f1 type kna1-kunnr,
f2 type kna1-name1,
end of fs.
Here by adding the clause 'occurs 0', memory will allocates to the fieldstring/wa i.e. definition of body.
By adding the clause 'with header line', fs acts as body as well as work area.
WORK AREA is one which represents all the fields of the referenced one.
Eg. wa like kna1 (occurs 0 / with header line).
The clauses 'occurs 0', 'header line' means the same as above.
If u find it useful, reward me plz.