Publish and Subscribe Overview
Publish and Subscribe Overview
Publish and subscribe messaging works based on the runtime interactions between:
Messages
A message is a production message. An external system receives a request and directs it into InterSystems IRIS, which converts it to a production message and sends it to a special-purpose business operation for processing.
Topics
A topic is a string that characterizes the contents of a message. InterSystems IRIS does not define any topics; users and their applications define the meanings of topics and subtopics.
A topic string has the form A.B.C.D, where A, B, C, and D are subtopic strings delimited by the . (period) character. A topic can contain any number of subtopics; each of these subtopics can be up to 50 characters long. The following are all valid topic strings:
books books.fiction books.fiction.latin
You can specify a range of topics by using * (the asterisk) as a wildcard character. For example:
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* can replace any complete subtopic in the topic string (books.*.latin works)
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* does not work as a partial wildcard (*s.fiction does not work; it does not match books.fiction, reviews.fiction, or any similar string)
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A trailing * character matches any number of additional subtopics to the right of the last . (period) character in the topic string (books.* matches books.fiction and books.fiction.latin)
Subscribers
A subscriber is an entity (a user or an external system) that might be interested in a specific topic or set of topics. A subscriber entry specifies how that entity wishes to be contacted; that is, how InterSystems IRIS should send a message to it.
Subscriptions
A subscription associates a subscriber with a topic string.
Suppose you have three subscribers:
Abel Baker Charlie
And three topics with the convention that A.B.C represents person.location.identifer:
Doctor.ICU.88495 Patient.LAB.* *.*.X3562564
In that case, you could define the following subscriptions:
| Subscriber | Topic |
|---|---|
| Abel | Doctor.ICU.88494 |
| Abel | Doctor.ICU.88495 |
| Baker | Doctor.ICU.88495 |
| Baker | Patient.LAB.* |
| Charlie | *.*.X3562564 |
This means:
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Abel is notified whenever the exact topics Doctor.ICU.88494 or Doctor.ICU.88495 are processed.
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Baker is notified whenever the exact topic Doctor.ICU.88495 is processed. In addition, Baker is notified whenever any message related to patients in the lab are processed.
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Charlie is notified whenever anything related to a doctor or patient with an identifier of X3562564 is processed.
