Context and nodes

what is a context ?, what is a node ? in web dynpro for ABAP

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Context

Context is a temporary place where we declare data deceleration's in the form of nodes and attributes.

Attribute

It is used to store a single value, these are similar to fields in table or structure.

Ex: MATNR, MTART, VBELN

Node

Node is a collection of attributes, it is similar to structure or internal table.

Properties of node

Cardinality

It specifies how many records that can be stored in a node, four options are available under cardinality.

Minimum Maximum Description
0 1 Node can store only one record i:e same as work area.
Node can only be filled through back end logic only ( can not be used for user input ).
1 1 Node can store only one record I:e same as work area
Node can be used for user input .
0 n
Node can store maximum 'n' number of records.
Node can only be filled through back end logic only ( can not be used for user input )
1 n
Node can store 'N' number of records I:e same as internal table
Node can be used for user input .

If maximum value = 1, it can store 1 record.
If maximum value = n, it can store 'N' records.

If minimum value = 0, data is selected from back end (using select, itab etc).
If minimum value = 1, data can be selected from front end (user input).

Understanding for Basic Users

For basic understanding, here I am comparing web dynpro with ABAP.

In ABAP we declare internal table like below.

DATA : IT_MARA TYPE TABLE OF MARA.

In web dynpro we create a node for mara with cardinality 0-n or 1-n, both can store 'n' number of records(Internal table can store n records).In future lesson we will learn when to take 0-n and 1-n cardinality for creating a node.

In ABAP we declare work area like below.

DATA : wa_MARA TYPE MARA.

In web dynpro we create a node for mara with cardinality 0-1 or 1-1, both can store one record only(work area can store only one record).In future lessons we will learn when to take 0-1 and 1-1 cardinality .

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