Github user kl0u commented on a diff in the pull request:
https://github.com/apache/flink/pull/2154#discussion_r68731943
--- Diff: docs/apis/streaming/windows.md ---
@@ -24,1023 +24,593 @@ specific language governing permissions and
limitations
under the License.
-->
+Flink uses a concept called *windows* to divide a (potentially) infinite
`DataStream` into slices
+based on the timestamps of elements or other criteria. This division is
required when working
+with infinite streams of data and performing transformations that
aggregate elements.
+
+<span class="label label-info">Info</span> We will mostly talk about
*keyed windowing* here, this
+means that the elements are subdivided based on both window and key before
being given to
+a user function. Keyed windows have the advantage that work can be
distributed across the cluster
+because the elements for different keys can be processed in isolation. If
you absolutely must,
+you can check out [non-keyed windowing](#non-keyed-windowing) where we
describe how non-keyed
+windows work.
+
* This will be replaced by the TOC
{:toc}
-## Windows on Keyed Data Streams
-
-Flink offers a variety of methods for defining windows on a `KeyedStream`.
All of these group elements *per key*,
-i.e., each window will contain elements with the same key value.
+## Basics
-### Basic Window Constructs
+For a windowed transformations you must at least specify a *key* (usually
in the form of a
--- End diff --
you must specify 1) a KeySelector, which will provide the key an element is
associated with, 2) a *window assigner* and 3) a *window function*.
---
If your project is set up for it, you can reply to this email and have your
reply appear on GitHub as well. If your project does not have this feature
enabled and wishes so, or if the feature is enabled but not working, please
contact infrastructure at [email protected] or file a JIRA ticket
with INFRA.
---
