Personal Eventing Protocol (XEP-0163)  introduced the idea of a virtual Publish-Subscribe (XEP-0060)  service associated with an IM user's bare JID <email@example.com>. However, the default node configuration options associated with PEP nodes are not optimized for the persistent storage of semi-public data objects such as public keys or user profiles. Therefore this document defines a set of best practices that enable IM users to persistently store semi-public data objects at their virtual pubsub service; in effect, we "sub-class" PEP by showing how a particular pubsub node can be configured for persisting objects.
Imagine that you are a Shakespearean character named Juliet and that you want to persistently store information such as your public keys (see Public Key Publishing (XEP-0189) ) and user profile (see User Profile (XEP-0154) ).
We assume that you have three contacts with the following relationship to you:
We also assume that your server (capulet.lit) supports PEP along with the "publish-options" feature, and that your client discovered that support when you logged in.
Because you want to keep your communications with Romeo confidential, you decide to start encrypting your messages. Therefore you reconfigure your client, which generates an RSA key that it publishes to the virtual pubsub service hosted at your bare JID <firstname.lastname@example.org>.
Your publish request is a standard pubsub request except that:
(In this case, access is limited to people in your Friends roster group.)
If all goes well (see Publishing an Item), your key will be pushed out to all appropriate individuals (in this case only Romeo). In particular, Romeo receives your key because he has auto-subscribed to the virtual pubsub service at your bare JID via a presence subscription and because his Entity Capabilities (XEP-0115)  data indicated that he is interested in the "urn:xmpp:tmp:pubkey" payload type.
Because PEP services must send notifications to the account owner, you too receive the notification at each of your resources (here "balcony" and "chamber").
So that's the general idea.
The best practices described herein re-use the concepts already defined in XEP-0060 and XEP-0163. In order to optimize for object persistence instead of transient event notifications, a node MUST be configured as follows:
The access model MAY be any model defined in XEP-0060.
An account owner publishes an item to a node by following the protocol specified in XEP-0060:
If the node does not already exist, the virtual pubsub service MUST create the node. As described in XEP-0163, this "auto-create" feature (defined in XEP-0060) MUST be supported by a PEP service. (Naturally, the account owner's client MAY follow the node creation use case specified in XEP-0060 before attempting to publish an item.)
In order for the client to reliably persist objects, the virtual pubsub service must also support the "publish-options" feature defined in XEP-0060. Typically, a client will publish with options so that the object is properly persisted.
If the publication logic dictates that event notifications shall be sent, the account owner's server generates notifications and sends them to all appropriate entities as described in the Receiving Event Notifications section of XEP-0163.
Each item published to the node is a logically separate instance of the data to be stored. It is the responsibility of the publishing and receiving entities to construct a complete view of all such items, if desired. For example, each bookmark published to a private data node is a separate piece of data, whereas the history of all items published to the node provides a complete list of the user's bookmarks. This history may include items that are republished with an existing ItemID (thus overwriting the previous version of that item).
Before an account owner attempts to complete the use cases defined herein, its client SHOULD verify that the account owner's server supports both PEP and the "publish-options" feature; to do so, it MUST send a Service Discovery (XEP-0030)  information request to the server (or cache Entity Capabilities information received from the server).
The server MUST return an identity of "pubsub/pep" and include the "publish-options" feauture in the list of the namespaces and other features it supports:
This document introduces no security considerations above and beyond those specified in XEP-0060 and XEP-0163.
This document requires no interaction with the Internet Assigned Numbers Authority (IANA) .
This document requires no interaction with the XMPP Registrar .
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The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 6120) and XMPP IM (RFC 6121) specifications contributed by the XMPP Standards Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this document has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.
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Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/
Per a vote of the XMPP Council, advanced specification to Active.
Added text about composition model, and modified examples accordingly.
Removed hokey acronym; changed type to Informational; clarified text.
Initial published version.