Enterprise messaging supports central messaging concepts:
Queues
A queue is a collection in which the entities in the collection are kept in order and the main operations on the queue are the addition of entities to the rear terminal position and removal of entities from the front terminal position.
Enterprise messaging enables applications to communicate with each other through message queues. A sending application sends a message to a specific named queue. There’s a one-to-one correspondence between a receiving application and its queue. The message queue retains the messages until the receiving application consumes it. You can manage these queues using the enterprise messaging dashboard.
Topics
Topics are named logical channels to which messages are published. Subscribers in a topic-based system receive all messages published to the topics to which they have subscribed. All subscribers to a topic receive their own copy of the same message.
Enterprise Messaging enables a sending application to publish messages and events to a topic. Applications must be subscribed to that topic and be active when the message is sent. Topics do not retain messages. This method can be used when each message needs to be consumed by a number of receiving applications.
Queue Subscriptions
With queue subscriptions Enterprise Messaging enables a sending application to publish messages to a topic. The topic sends the message directly to the queue to which it is bound. For example, events from an SAP S/4HANA system (event source) can only be sent to a topic. A queue subscription ensures that the message is retained until it is consumed by the receiving application.
Message Client
A message client allows you to connect to the Enterprise Messaging service using its own unique credentials to send and receive messages. The client can run within SAP Cloud Platform or outside it.
You can create multiple message clients that can be distinguished by a set of credentials that consist of a namespace and connection rules that define the list of queues or topics to which the message client can send and receive messages.
The namespace is a unique prefix that defines all the queues or topics that have been created in the context of a particular message client. When you manage queues or topics in Enterprise Messaging, the namespace allows message clients to identify the queues or topics for communication.