Changeset 1251 for draft-ietf-httpbis/latest/p4-conditional.xml

Timestamp:

Mar 31, 2011, 5:11:25 AM (9 years ago)

Author:

fielding@…

Message:

editorial: rewrite introduction to p4 conditionals and compress some
the references to ABNF in other parts so that they don't impede the
readability of this part. Add informative ref to WebDAV spec.

Addresses #228

File:

• draft-ietf-httpbis/latest/p4-conditional.xml (modified) (5 diffs)

draft-ietf-httpbis/latest/p4-conditional.xml

@@ -216 +216 @@
 <section title="Introduction" anchor="introduction">
 <t>
-   This document defines HTTP/1.1 response metadata for indicating potential
-   changes to payload content, including modification time stamps and opaque
-   entity-tags, and the HTTP conditional request mechanisms that allow
-   preconditions to be placed on a request method.  Conditional GET requests
-   allow for efficient cache updates.  Other conditional request methods are
-   used to protect against overwriting or misunderstanding the state of a
-   resource that has been changed unbeknownst to the requesting client.
+   This document defines the HTTP/1.1 conditional request mechanisms,
+   including both response metadata that can be used to indicate or
+   observe changes to resource state and request header fields that
+   specify preconditions to be checked before performing the action
+   given by the request method.  Conditional GET requests are the most
+   efficient mechanism for HTTP cache updates.  Conditionals can be
+   applied to state-changing methods, such as PUT and DELETE, to prevent
+   the "lost update" problem: one client accidentally overwriting
+   the work of another client that has been acting in parallel.
+</t>
+<t>
+   Conditional request preconditions are based on the state of the target
+   resource as a whole (its current value set) or the state as observed
+   in a previously obtained representation (one value in that set).
+   A resource might have multiple current representations, each with its
+   own observable state.  The conditional request mechanisms assume that
+   the mapping of requests to corresponding representations will be
+   consistent over time if the server intends to take advantage of
+   conditionals.  Regardless, if the mapping is inconsistent and
+   the server is unable to select the appropriate representation, then
+   no harm will result when the precondition evaluates to false.
 </t>
 <t><iref primary="true" item="selected representation"/>
-   We use the term "<x:dfn>selected representation</x:dfn>" to refer to the current
-   representation of the target resource that would have been selected
-   and sent as payload in a 200 (OK) response if the same request had used
-   the method GET and had excluded all of the conditional request header
-   fields.  The conditions found within conditional requests are evaluated
-   on the basis of either the state of the target resource as a whole or
-   the state of the target resource's selected representation.
-</t>
-<t>
-   This document is currently disorganized in order to minimize the changes
-   between drafts and enable reviewers to see the smaller errata changes.
-   A future draft will reorganize the sections to better reflect the content.
-   In particular, the sections on resource metadata will be discussed first
-   and then followed by each conditional request header field, concluding with a
-   definition of precedence and the expectation of ordering strong validator
-   checks before weak validator checks.  It is likely that more content from
-   &caching; will migrate to this part, where appropriate.
-   The current mess reflects how widely dispersed these topics and associated
-   requirements had become in <xref target="RFC2616"/>.
+   We use the term "<x:dfn>selected representation</x:dfn>" to refer to
+   the current representation of the target resource that would have been
+   selected in a successful response if the same request had used the method
+   GET and had excluded all of the conditional request header fields.
+   The conditional request preconditions are evaluated by comparing the
+   values provided in the request header fields to the current metadata
+   for the selected representation.
 </t>
 
@@ -271 +273 @@
   <x:anchor-alias value="VCHAR"/>
   <x:anchor-alias value="WSP"/>
+  <x:anchor-alias value="core.rules"/>
+  <x:anchor-alias value="quoted-string"/>
+  <x:anchor-alias value="OWS"/>
+  <x:anchor-alias value="HTTP-date"/>
 <t>
   This specification uses the ABNF syntax defined in &notation; (which
@@ -287 +293 @@
   and WSP (whitespace).
 </t>
-
-<section title="Core Rules" anchor="core.rules">
-  <x:anchor-alias value="quoted-string"/>
-  <x:anchor-alias value="OWS"/>
-<t>
-  The core rules below are defined in &basic-rules;:
+<t>
+  The ABNF rules below are defined in other parts:
 </t>
 <figure><artwork type="abnf2616">
   <x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in &basic-rules;&gt;
   <x:ref>OWS</x:ref>           = &lt;OWS, defined in &basic-rules;&gt;
-</artwork></figure>
-</section>
-
-<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
-  <x:anchor-alias value="HTTP-date"/>
-<t>
-  The ABNF rules below are defined in other parts: 
-</t>
-<figure><!--Part1--><artwork type="abnf2616">
   <x:ref>HTTP-date</x:ref>     = &lt;HTTP-date, defined in &full-date;&gt;
 </artwork></figure>
 </section>
-
-</section>
-
-</section>
-
-<section title="Entity-Tags" anchor="entity.tags">
+</section>
+
+<section title="Resource State Metadata" anchor="resource.metadata">
+<t>
+   This specification defines two forms of metadata that are commonly used
+   to observe resource state and test for preconditions: modification dates
+   and opaque entity tags.  Additional metadata that reflects resource state
+   has been defined by various extensions of HTTP, such as WebDAV
+   <xref target="RFC4918"/>, that are beyond the scope of this specification.
+</t>
+
+<section title="Entity Tags" anchor="entity.tags">
   <x:anchor-alias value="entity-tag"/>
   <x:anchor-alias value="opaque-tag"/>
@@ -406 +405 @@
   </t>
 </x:note>
+</section>
 </section>
 </section>
@@ -1445 +1445 @@
 </reference>
 
+<reference anchor='RFC4918'>
+  <front>
+    <title>HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)</title>
+    <author initials="L.M." surname="Dusseault" fullname="Lisa Dusseault" role="editor" >
+      <organization abbrev="CommerceNet">CommerceNet</organization>
+      <address><email>ldusseault@commerce.net</email></address>
+    </author>
+    <date month="June" year="2007" />
+  </front>
+  <seriesInfo name='RFC' value='4918' />
+</reference>
 </references>