Strong and Weak Validation
The ETag mechanism supports both strong validation and weak validation. They are distinguished by the presence of an initial "W/" in the ETag identifier, as:
"123456789" -- A strong ETag validator W/"123456789" -- A weak ETag validatorA strongly validating ETag match indicates that the content of the two resources is byte-for-byte identical and that all other entity fields (such as Content-Language) are also unchanged. Strong ETags permit the caching and reassembly of partial responses, as with byte-range requests.
A weakly validating ETag match only indicates that the two resources are semantically equivalent, meaning that for practical purposes they are interchangeable and that cached copies can be used. However the resources are not necessarily byte-for-byte identical, and thus weak ETags are not suitable for byte-range requests. Weak ETags may be useful for cases in which strong ETags are impractical for a web server to generate, such as with dynamically-generated content.
Read more about this topic: HTTP ETag
Famous quotes containing the words strong and, strong and/or weak:
“Reason looks at necessity as the basis of the world; reason is able to turn chance in your favor and use it. Only by having reason remain strong and unshakable can we be called a god of the earth.”
—Johann Wolfgang Von Goethe (17491832)
“The weak are the most treacherous of us all. They come to the strong and drain them. They are bottomless. They are insatiable. They are always parched and always bitter. They are everyones concern and like vampires they suck our lifes blood.”
—Bette Davis (19081989)
“His misfortune was that he loved youthhe was weak to it, it kindled him. If there was one eager eye, one doubting, critical mind, one lively curiosity in a whole lecture-room full of commonplace boys and girls, he was its servant. That ardour could command him. It hadnt worn out with years, this responsiveness, any more than the magnetic currents wear out; it had nothing to do with Time.”
—Willa Cather (18731947)