Github user tzulitai commented on a diff in the pull request:
https://github.com/apache/flink/pull/4041#discussion_r119606506
--- Diff: docs/dev/libs/cep.md ---
@@ -98,48 +128,105 @@ val result: DataStream[Alert] =
patternStream.select(createAlert(_))
</div>
</div>
-Note that we use Java 8 lambdas in our Java code examples to make them
more succinct.
-
## The Pattern API
-The pattern API allows you to quickly define complex event patterns.
-
-Each pattern consists of multiple stages or what we call states.
-In order to go from one state to the next, the user can specify conditions.
-These conditions can be the contiguity of events or a filter condition on
an event.
-
-Each pattern has to start with an initial state:
+The pattern API allows you to quickly define complex pattern sequences
that you want to extract
+from your input stream.
+
+Each such complex pattern sequence consists of multiple simple patterns,
i.e. patterns looking for
+individual events with the same properties. These simple patterns are
called **states**. A complex pattern
+can be seen as a graph of such states, where transition from one state to
the next happens based on user-specified
+*conditions*, e.g. `event.getName().equals("start")`. A *match* is a
sequence of input events which visit all
+states of the complex pattern graph, through a sequence of valid state
transitions.
+
+<span class="label label-danger">Attention</span> Each state must have a
unique name to identify the matched
+events later on.
+
+<span class="label label-danger">Attention</span> State names **CANNOT**
contain the character `:`.
+
+In the remainder, we start by describing how to define [States](#states),
before describing how you can
+combine individual states into [Complex Patterns](#combining-states).
+
+### Individual States
+
+A **State** can be either a *singleton* state, or a *looping* one.
Singleton states accept a single event,
+while looping ones accept more than one. In pattern matching symbols, in
the pattern `a b+ c? d` (or `a`,
+followed by *one or more* `b`'s, optionally followed by a `c`, followed by
a `d`), `a`, `c?`, and `d` are
+singleton patterns, while `b+` is a looping one (see
[Quantifiers](#quantifiers)). In addition, each state
+can have one or more *conditions* based on which it accepts events (see
[Conditions](#conditions)).
--- End diff --
Perhaps somewhere in this paragraph, describe that by default, states are
singleton? and to make it a looping one, use quantifiers.
There is a sentence mentioning for looping state see quantifiers, but we
can make the information a bit more explicit.
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