The three-level type hierarchy, table definitions and indexes, buffering, and foreign keys and search helps.
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The Data Dictionary holds every data definition in the system โ tables, views, types and search helps โ 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 โ an amount domain used by invoice amount and payment amount โ 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