Basic Concepts

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This section tries to clarify some of the technical jargon used along with feed readers.

### What does "online/offline desktop" news aggregator mean?

Feed readers or news aggregators can be realised as web applications or as desktop applications. The place of execution (your computer vs. some webserver) implies certain advantages and disadvantages.

A desktop news aggregator runs on your own PC and stores aggregated feeds locally. It accesses each news feed and downloads its newest headlines periodically. Note that not all desktop news aggregators can work offline. Some desktop aggregators retrieve feeds each time you access them instead of caching them for later use. Liferea as an offline capable desktop aggregator caches feeds and is suitable for use with portable devices (laptops, hand helds...) that do not have a permanent internet connection.

- Disadvantages:
  - No implicit state synchronization when used from different client machines
  - Higher bandwidth usage compared to online aggregators
  - Need to be installed on each client machines
  - OS-dependant
- Advantages:
  - Your cached feed contents are saved on your own (secure) machine.
  - Your cached feed contents are searchable locally with other tools (e.g. Beagle)
  - Your feed list is not accessible to 3rd parties
  - Each feed access are done in private.

A online news aggregator (for example TheOldReader) is run on a remote webserver which you can access from everywhere as long as you have network access. When you log in to the online news aggregator it usually doesn't need to fetch the most recent headlines of you feed subscriptions because it implements feed caching to save bandwidth.

- Disadvantages:
  - You rely on some 3rd party vendor for the news aggregator service.
  - Often you have to pay for premium features.
  - No chance to improve/modify/fix the online application.
  - You need a web browser to access it.
- Advantages:
  - You get the same feed list and feed states no matter from where you access them.
  - Practically no bandwidth usage except for the access of the web interface.
  - Community headline rating systems to categorize content.
  - Sharing headlines with the community (or specific users).

### What is a Feed?

For a news aggregator a news feed is a distinct information source. A news aggregator usually retrieves news headlines from many news feed subscriptions. The term "news feed" is not very precise as feeds can also provide weblog postings, podcasts and practically every type of content. The same goes for the term "news headlines": often "article" or "post" would be a better description. Nonetheless the prefix "news" is usually used with the terms "feed", "headline" and "aggregator".

When you add a new subscription then you have to specify the source of the feed so that the news aggregator can initially retrieve it. The feed source is usually a HTTP URL. When updating the news feed the aggregator downloads the document served when accessing this URL. There are several XML-based and XML-like syndication standards (RSS, Atom...) that define how a feed must look like so that the aggregator knows how to interpret the document contents.

As a user you usually do not have to know about the syndication format. You just need to know the source URL of the feed you want to subscribe.

### What is the Feed List?

Typical news aggregators present you with a list of your feed subscription. Following the email client interface paradigm the feed list is often presented in the left pane of the news aggregator interface.

Depending on the aggregator you use the feed list might be hierarchically organized using folders or categories.

### What is a Headline?

When a news aggregator updates a news feed it download the source document from the source URL of the feed subscription. This source document provides a set of the most recent headlines which then need to be merged against the current feed cache of the aggregator because the set of headlines provided by the feed source changes over time.

Headlines as provided by the feed source are the smallest information unit handled by aggregators.

### What is the Item List?

In Liferea headlines are also called items and are presented in the so called item list. Following the email client paradigm the item list is often presented in the upper right pane in the news aggregator interface.

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