Data Dictionary

The three-level type hierarchy, table definitions and indexes, buffering, and foreign keys and search helps.

The Data Dictionary holds every data definition in the system — tables, views, types and search helps — and is reached through SE11.

Three levels of type

Domain, data element, field

Level	Defines	Example
Domain	Technical attributes: type, length, value range, conversion routine	MATNR18
Data element	Semantic attributes: labels, documentation, search help	MATNR, labelled "Material"
Table field	A column in a table	MARA-MATNR

Several data elements can share a domain — an amount domain used by invoice amount and payment amount — identical technically, different in meaning and label.

Table definition

Parts of a table definition

Element	Content
Fields	Columns, referencing data elements
Primary key	The fields that uniquely identify a row
Delivery class	Master, transaction or customising data
Maintenance settings	Whether display and maintenance are permitted
Technical settings	Data class, size category, buffering
Indexes	Secondary indexes for faster access

Indexes

When an index helps

" Index on (WERKS, MATNR, LGORT)

WHERE werks = '1000'                          " helps
WHERE werks = '1000' AND matnr = 'MAT-001'    " helps
WHERE matnr = 'MAT-001'                        " little help
WHERE werks = '1000' AND lgort = '0001'       " little help

Buffering

Buffering options

Kind	Behaviour	Suited to
Full	Whole table held in memory	Small customising tables
Generic	Rows matching the first N key fields	Settings per client or plant
Single record	Only accessed rows	Frequently read rows of a large table
None	Always read the database	Transaction data

Other Dictionary objects

Object	Purpose
Table	Storing data
View	Joining tables or restricting fields
Data element / domain	Type definitions
Structure	A record type that is not a table
Table type	An internal table type
Search help	F4 value help
Lock object	Concurrency control; generates ENQUEUE and DEQUEUE functions