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:
“The myths about what we’re supposed to feel as new mothers run strong and deep. . . . While joy and elation are surely present after a new baby has entered our lives, it is also within the realm of possibility that other feelings might crop up: neediness, fear, ambivalence, anger.”
—Sally Placksin (20th century)
“When thou, poor Excommunicate
From all the joys of love, shalt see
The full reward and glorious fate
Which my strong faith shall purchase me,
Then curse thine own inconstancy!”
—Thomas Carew (1589–1639)
“We have no participation in Being, because all human nature is ever midway between being born and dying, giving off only a vague image and shadow of itself, and a weak and uncertain opinion. And if you chance to fix your thoughts on trying to grasp its essence, it would be neither more nor less than if your tried to clutch water.”
—Michel de Montaigne (1533–1592)