Trackbacks were originally developed by SixApart (http://www.sixapart.com/), creators of the MovableType (http://www.movabletype.org/) blog package. SixApart has a good introduction to trackbacks (http://www.movabletype.org/trackback/beginners/):
In a nutshell, TrackBack was designed to provide a method of notification between websites: it is a method of person A saying to person B, “This is something you may be interested in.” To do that, person A sends a TrackBack ping to person B.
A better explanation is this:
- Person A writes something on their blog.
- Person B wants to comment on Person A’s blog, but wants her own readers to see what she had to say, and be able to comment on her own blog
- Person B posts on her own blog and sends a trackback to Person A’s blog
- Person A’s blog receives the trackback, and displays it as a comment to the original post. This comment contains a link to Person B’s post
The idea here is that more people are introduced to the conversation (both Person A’s and Person B’s readers can follow links to the other’s post), and that there is a level of authenticity to the trackback comments because they originated from another weblog. Unfortunately, there is no actual verification performed on the incoming trackback, and indeed they can even be faked.
Most trackbacks send to Person A only a small portion (called an “excerpt”) of what Person B had to say. This is meant to act as a “teaser”, letting Person A (and his readers) see some of what Person B had to say, and encouraging them all to click over to Person B’s site to read the rest (and possibly comment).
Person B’s trackback to Person A’s blog generally gets posted along with all the comments. This means that Person A can edit the contents of the trackback on his own server, which means that the whole idea of “authenticity” isn’t really solved. (Note: Person A can only edit the contents of the trackback on his own site. He cannot edit the post on Person B’s site that sent the trackback.)
Pingbacks were designed to solve some of the problems that people saw with trackbacks. The official pingback documentation (http://www.hixie.ch/specs/pingback/pingback) makes pingbacks sound an awful lot like trackbacks:
For example, Alice writes an interesting article on her Web log. Bob reads Alice’s article and comments about it, linking back to Alice’s original post. Using pingback, Bob’s software can automatically notify Alice that her post has been linked to, and Alice’s software can then include this information on her site.
There are three significant differences between pingbacks and trackbacks, though.
- Pingbacks and trackbacks use drastically different communication technologies (XML-RPC and HTTP POST, respectively).
- Pingbacks support auto-discovery where the software automatically finds out the links in a post, and automatically tries to pingback those URLs, while trackbacks must be done manually by entering the trackback URL that the trackback should be sent to.
- Pingbacks do not send any content.
The best way to think about pingbacks is as remote comments:
- Person A posts something on his blog.
- Person B posts on her own blog, linking to Person A’s post. This automatically sends a pingback to Person A when both have pingback enabled blogs.
- Person A’s blog receives the pingback, then automatically goes to Person B’s post to confirm that the pingback did, in fact, originate there.
The pingback is generally displayed on Person A’s blog as simply a link to Person B’s post. In this way, all editorial control over posts rests exclusively with the individual authors (unlike the trackback excerpt, which can be edited by the trackback recipient). The automatic verification process introduces a level of authenticity, making it harder to fake a pingback.
Some feel that trackbacks are superior because readers of Person A’s blog can at least see some of what Person B has to say, and then decide if they want to read more (and therefore click over to Person B’s blog). Others feel that pingbacks are superior because they create a verifiable connection between posts.
Verifying Pingbacks and Trackbacks
Comments on blogs are often criticized as lacking authority, since anyone can post anything using any name they like: there’s no verification process to ensure that the person is who they claim to be. Trackbacks and Pingbacks both aim to provide some verification to blog commenting.