Lecture 7: Internet Applications #3.3: HTTP/1.1

Entity Tags in HTTP/1.1

The "Entity Tag" is new in HTTP/1.1 and is used to indicate that two (perhaps apparently unrelated) resources are in fact the same. For example, requests for each of the two Web pages:

http://ironbark.bendigo.latrobe.edu.au/subjects/int21cn/news.html
http://ironbark.bendigo.latrobe.edu.au/subjects/int31bcn/news.html

Both return the same Entity Tag header:

ETag: "1cc30e3-88e-404e6d9b"

The client can use an If-None-Match: "1cc30e3-88e-404e6d9b"
request header with a GET request to specify the version of the object which it already has. This is a significant improvement over the HTTP/1.0 "Conditional-GET" -- although not all entities are (by default) generated with Entity Tags.

You can discover lots more about HTTP/1.1 at: http://www.w3.org/pub/WWW/Protocols/Specs.html

Lecture 7: Internet Applications #3.3: HTTP/1.1

The tutorial for this lecture is Tutorial #7.
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