Subject Name Syntax
Subject-based addressing™ technology places few restrictions on the syntax and interpretation of subject names. System designers and developers have the freedom (and responsibility) to establish conventions for using subject names. The best subject names reflect the structure of data in the application itself.
Each subject name is a string of characters that is divided into elements by the dot (.) character. It is illegal to incorporate the dot character into an element by using an escape sequence.
Rendezvous limits subject names to a total length of 255 characters (including dot separators). However, some of that length is reserved for internal use.
The longest subject that (most) programs can receive is 196 characters.
The maximum total length (in characters) of subjects that your programs may send is 196 minus the number of elements. Include dot separators in this total.
The maximum element length is 127 characters (dot separators are not included in element length).
Typical subject names are shorter and use fewer elements. For maximum speed and throughput rates, use short subject names. For details, see Subject Name Performance Considerations.
The empty string (““) is not a legal subject name.
Examples
These examples illustrate the syntax for subject names.
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Special Characters in Subject Names
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Char |
Char Name |
Special Meaning |
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Underscore |
Reserved Subject Names Warning Subject names beginning with underscore are reserved. It is illegal for application programs to send to subjects with underscore as the first character of the first element, except It is legal to use underscore elsewhere in subject names. |
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Dot |
Separates elements within a subject name. |
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Greater-than |
Wildcard character, matches one or more trailing elements. |
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Asterisk |
Wildcard character, matches one element. |
It is good practice to avoid using tabs, spaces, or any unprintable character in a subject name.
For information about wildcard characters and matching, see Using Wildcards to Receive Related Subjects.