# System Property Fields

Substation ES system fields, or properties as they are known in JMS (EMS), are mostly optional, but might either be present in the message or as a property in message.

For a full list of system fields, see "System Fields" in the TIBCO Substation ES Configuration and Resources guide.

To ensure that the contents of these system fields are correctly processed by Substation ES and relayed to a particular interface, application or applications payload system, fields must be defined correctly in the configuration.

Note: Only TIBCO EMS handles system fields, referred to in this case as properties, outside of the application payload. However, within EMS these system fields might occasionally appear in both a property and in the payload. When this is the case, Substation ES uses the ESB parameter EMS-USE-PROP to determine where to look for the fields.

For best results, configure EMS messages to use properties alone, and do not place system fields within the application payload when using EMS MAP type messages.

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