Learn sap abap in 20 days part 3.

Data dictionary:
The ABAP Data Dictionary centrally describes the logical structures of the objects used in application development
and shows how they are mapped to the underlying relational database in tables/views.
IS a system independent interface to the database systemis a virtual database (data about data)provide data for data manipulation and data processing   also called DDIC and ABAP DICTIONARY.

data types in sap abap:-
Data types:
1.Pure type description
2.Do not occupy their own MEMEORY space
3.Characterize the technical attributes of all data objects that have a particular type.
4.Either built in or defined types.
data types is of two types in sap abapelementry and non-elementry or customer defined.
in elementry CHAR,INT,PACKED,FLOAT,NUMC,DATE,TIME,HEXADECIMAL.
AND IN NON-ELEMENTRY internal tables and work area packed is in the compressed form that tells us about the rounding errors. the data objects are nothing but the data containers

Commands in sap:-
First and most important statement is:-
WRITE f TO g[+off][(len)].
WRITE f TO itab[+off][(len)] INDEX idx.
   1.concatenate
   2.condense
   3.replace
   4.shift
   5.split
   6.translate
   example for translate command:-
   TRANSLATE c TO UPPER CASE.
                    TRANSLATE c TO LOWER CASE.
                    Example :
                    DATA letters(3) TYPE C.
                    MOVE ‘xyz' TO letters. TRANSLATE letters TO UPPER CASE.
                    TRANSLATE letters TO UPPER CASE</