June 2000
Beginner to intermediate
80 pages
2h 49m
English
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Entity Tags
In HTTP 1.1, a new method of cache management involves entity tags. The problem solved by entity tags is that there may be several copies of the same document on the server. The client has no way of knowing that it’s the same document—so even if it the client already has a copy of the document, the client will request the document again.
Entity tags are unique identifiers that can be associated with all
copies of the document. If the document changes, the entity tag
changes—so it is more efficient to check for the entity tag,
not for the URL and Last-Modified date.
If the server uses entity tags, it sends the document with the
ETag
header. When the client wants to verify
if a document matches a particular entity tag, it uses the
If-Match or
If-None-Match header.
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