Communication Ethics book part for How Does Annotation Work Technically?. (This is an automatically generated summary to avoid having huge posts on this page. Click through to read this post.)

How the annotation author leaves a note on a given page, and how it is shown to the annotation viewer, worked like this:

1. The annotation author would request a web page, let us say http://www.jerf.org for concreteness, from the web server. The browser would retrieve it normally.
2. Once the browser was done retrieving the page normally, the annotation program, which was a plug-in to the browser and thus deeply integrated with the browser so it could detect things like when the page was done loading, would send a query off to the annotation server, asking if there are any notes for "http://www.jerf.org/ ".
3. In this case, we'll say there wasn't any yet, so the server returns that there are no notes on that page yet.
4. When the user decides to leave a note, he tells his annotation software where he wants to leave it, and what the title and contents should be.
5. The annotation software reports to the annotation server the contents of the note and where to put it.
6. When another user of the same program goes to http://www.jerf.org/ , their browser downloads the web page.
7. Their annotation program asks the annotation server whether there are any notes on the page.
8. This time, the server reports that there is a note on that page, and sends it to the annotation program, which then allows the user to browse it.

One consequence of this design is that only other users of the particular annotation software can see the annotations on that system. Different software systems can have entirely separate databases of annotations, and conceivably if this technology ever takes off, someone might build a "meta-annotation" software program that could hook into many different annotation databases. Another one is that the annotation server gets a complete log of the pages visited by the user.

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Proxy-based annotation

The other major way that an annotation service can function is by using a proxy, which is a computer that acts on behalf of another computer. In this case, the proxy gets the web page for the requesting computer, and additionally adds the annotation information.

1. The user asks the browser for a web page, http://www.jerf.org.
2. The browser asks for that web page from the proxy.
3. The proxy retrieves the web page from http://www.jerf.org , and adds the annotations to the HTML. The proxy returns this modified HTML to the browser.
4. The browser displays the modified page.

Adding annotations is done by sending special requests through the browser, which the proxy server detects and processes to add the annotation into its internal database.

While very different technically (different bandwidth requirements, different bottlenecks in the system), the theoretical capabilities of the two techniques are identical. Some effects are easier in one model then the other, but there is nothing that is possible in one that is impossible in the other.