In SAP Cloud Integration, both the Aggregator and Gather steps are used to merge multiple messages into a single message.

The Aggregator is a stateful message processing step that collects a sequence of individual, related messages and combines them into a single message based on a defined correlation logic and completion condition.

The Gather step is used to collect messages processed in different parallel routes (typically initiated by a Multicast step) and merge them back into one message. It waits for all parallel branches to complete before combining the results.

B. Router: A Router directs a message to one of several alternative paths based on a condition. It does not merge messages; it makes a routing decision.

C. Multicast: A Multicast sends a copy of the same message to multiple parallel processing paths. It is a splitting mechanism, the opposite of merging.

1. SAP Help Portal

Cloud Integration - Aggregator: "The aggregator collects and stores a series of related incoming messages. As soon as a complete set of messages has been collected

the aggregator publishes a single message that is the result of a combination of the original messages."

Source: SAP Help Portal

Define Aggregator.

2. SAP Help Portal

Cloud Integration - Gather: "The Gather step allows you to merge messages from more than one route in an integration process. The Gather step collects messages that are processed in different routes and combines them into a single message."

Source: SAP Help Portal

Define Gather.

3. SAP Help Portal

Cloud Integration - Multicast: "A multicast allows you to route the same message to two or more different receivers and have the message processed in different ways." (The Gather step is used to join the results from these paths).

Source: SAP Help Portal

Define Parallel and Sequential Processing.

4. Hohpe

G.

& Woolf

B. (2003). Enterprise Integration Patterns: Designing

Building

and Deploying Messaging Solutions. Addison-Wesley.

The Aggregator pattern is described in Chapter 6

Message Transformation Patterns. It details the process of collecting related messages to form a single composite message.

The Scatter-Gather pattern is described in Chapter 8

Messaging Routing Patterns. The Gather step in SAP CPI is the implementation of the "gather" part of this pattern

which collects responses from the "scatter" phase (implemented by Multicast).