SAP ABAP - Data Dictionary

 Transparent tables:

1) Used to hold application data (master or transaction data)

2) 1:1 relation with the database table

3) Same name, same number of fields,

Pooled tables: (table pools)

Many to one relation ship with the database

Table pools holds number of pool tables

Table pools hold a large number of very small tables (10 to 100 rows each)

Used to hold control data (e.g. screen sequences,program parameters or temporary data).

Used to hold customizing data (country codes, region codes, .pricing conditions)

Cluster tables: (table clusters)

Many to one relation ship with the database

Table clusters is combinations cluster tables.

Table cluster holds data from a few (2 to 10) very large tables.

In order to combine tables in clusters, at least  parts of the keys must agree (performance good ) , but not in the case of pool.

Table: Creation

Delivery and maintenance:

Delivery class: identifies the owner of the data in this table, the owner is responsible for maintaining table contents.  Customer or sap or ……..

Technical settings: settings we can control how database tables are created in the database.

Data class:  Determines the in which table space the table is stored when table is created

Size category   Probable space requirement of the table in the database

                              Buffering

Table maintenance generator

Table maintenances generator is nothing but  making a table available for adding records anddeletingrecords.    The transaction code used is SM30.

Step 1

Create parameter transaction (i.e. via SE93)



Step 2
Enter transaction details. Within the Proposed values section there are a number of value which can be setup, simply use drop down menu to view the list. The 2 values assigned in the following example are as follows:
       
                VIEWNAME:        Set table name to maintained
               UPDATE:               Open table for update






Foreign
key:



FK is a field in table that is connected to
another table via foreign key relation ship.

Purpose of foreign key relationship is to
validate the data being entered into one table by checking against a valid set
of values in another table.





Limitations: 



Check table field must be primary key in
that table.



Domain names and check table field must be
same.





Cardinality: For each value in the check table, how many rows of data are allowed in the foreign key table.





Value Table:

Its like default
check table (But not), value table is automatically proposed as the



Check table when
creating a foreign key.





Currency and quantity fields:



Each currency
field must be linked to a currency key field, and each quantity field must be
linked to a field containing the units of measurement.



The value in the
reference field determines the currency of the amount. ( and also quantity)



Indexes :

Efficiency mechanism for quickly finding rows


with in a table.