Understand middleware client application database transactions

Each active MES middleware can process client application calls to perform MES database transactions. The middleware supports the following call endpoints.

Web API

The middleware listens for HTTPS calls (for encrypted communication) or HTTP calls (for unencrypted communication) on a specified port that's configurable. By default, HTTPS uses port 443 and HTTP uses port 80. These port assignments can be changed when configuring the System Management Server in the post‑install Configurator.

All versions of the MES Web API go through this endpoint.

Synchronous

When the client application makes a call, the transaction is attempted and the response is returned immediately. All Stateful API calls and most Stateless API calls go through this endpoint.

Asynchronous

When the client application makes a call, the transaction is attempted but no response is returned. If the requested transaction does not occur, an entry is added to the Rejected Message table. These entries can be viewed in MES Client, where the user can attempt to fix the request message and resubmit it.

• Asynchronous Stateless API calls go through this endpoint.

• The Utilization Capability Object (UCO) makes asynchronous calls to set the current utilization reason.

• The Operations Capability Object (OCO) makes asynchronous calls when configured in Without Response mode.

Event Broker

The Event Broker allows client applications to subscribe to MES database changes. For example, MES Client uses this service to keep its editors current. If two MES Client instances are running and an a database change is made from one, the editor data displayed in the other instance will be updated by this service.