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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.

Structure

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.

Length

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.

Empty String Illegal

The empty string (““) is not a legal subject name.

Examples

These examples illustrate the syntax for subject names.

Table 7 Valid Subject Name Examples 

NEWS.LOCAL.POLITICS.CITY_COUNCIL

NEWS.NATIONAL.ARTS.MOVIES.REVIEWS

CHAT.MRKTG.NEW_PRODUCTS

CHAT.DEVELOPMENT.BIG_PROJECT.DESIGN

News.Sports.Baseball

finance

This.long.subject_name.is.valid.even.though.quite.uninformative

 

Table 8 Invalid Subject Name Examples 

News..Natural_Disasters.Flood (null element)

WRONG. (null element)

.TRIPLE.WRONG.. (three null elements)

Special Characters in Subject Names

 

Table 9 Characters with Special Meaning in Subject Names (Sheet 1 of 2)

Char	Char Name	Special Meaning
_	Underscore	Reserved Subject Names   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 _INBOX and _LOCAL. It is legal to use underscore elsewhere in subject names.
.	Dot	Separates elements within a subject name.
>	Greater-than	Wildcard character, matches one or more trailing elements.
*	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.

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