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## Paradigms

### 1-1 or 1-n

### push or pull

### relaying aka intermediaries

## Separation of concerns

### Publishing

> "I want to share this with the world."

For a resource to be visible to other people, it must first be published. Typically, resources are published at a location or with a specific identifier; people who wish to view that resource can then go to that location or search for that identifier using a lookup service in order to view the resource. Most commonly, resources are published on the World Wide Web, and they are found via their uniform resource location (URL). When you type, paste, or click a link in your Web browser, your browser will make a request to fetch that resource on your behalf, and the server responsible for that resource will respond with the resource.

### Subscribing

> "I want to see the things I am interested in."

OK, so there are resources that we can access if they are published at a known location or with a known identifier. How do we know when there are new or updated resources? At the most basic level, you can manually check a resource to see if it has been updated; for example, you can check a website to see if there are any new pages. To make this manual checking process easier, publishers can generate a feed or stream of resources that can be subscribed to. When you subscribe to that feed, your feed reader will periodically check the feed for any changes; for example, a feed may be updated with the latest articles from a Web site, which your reader will then pull and show to you as an update.

### Messaging

> "I want to communicate directly with people."

In some ways, messaging can be covered by having a publisher and a subscriber on each end of a conversation, but it usually makes more sense to deliver messages to your conversational partners directly rather than having them check for new messages on their own schedule. 

### Discussing

> "I want to gather in a community or around a topic."

Traditionally, this has been handled by forums, bulletin board systems, and groups.