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https://issues.apache.org/jira/browse/FLINK-9947?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16563750#comment-16563750
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ASF GitHub Bot commented on FLINK-9947:
---------------------------------------
fhueske commented on a change in pull request #6456: [FLINK-9947] [docs]
Document unified table sources/sinks/formats
URL: https://github.com/apache/flink/pull/6456#discussion_r206536297
##########
File path: docs/dev/table/connect.md
##########
@@ -0,0 +1,1033 @@
+---
+title: "Connect to External Systems"
+nav-parent_id: tableapi
+nav-pos: 19
+---
+<!--
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements. See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership. The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License. You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied. See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+
+Flink's Table API & SQL programs can be connected to other external systems
for reading and writing both batch and streaming tables. A table source
provides access to data which is stored in external systems (such as a
database, key-value store, message queue, or file system). A table sink emits a
table to an external storage system. Depending on the type of source and sink,
they support different formats such as CSV, Parquet, or ORC.
+
+This page describes how to declare built-in table sources and/or table sinks
and register them in Flink. After a source, sink, or both have been registered,
they can be accessed by Table API & SQL queries.
+
+<span class="label label-danger">Attention</span> If you want to implement
your own *custom* table source or sink, have a look at the [user-defined
sources & sinks page](sourceSinks.html).
+
+* This will be replaced by the TOC
+{:toc}
+
+Dependencies
+------------
+
+The following table list all available connectors and formats. Their mutual
compatibility is tagged in the corresponding sections for [table
connectors](connect.html#table-connectors) and [table
formats](connect.html#table-formats). The following table provides dependency
information for both projects using a build automation tool (such as Maven or
SBT) and SQL Client with SQL JAR bundles.
+
+{% if site.is_stable %}
+
+### Connectors
+
+| Name | Version | Maven dependency | SQL
Client JAR |
+| :---------------- | :------------ | :--------------------------- |
:----------------------|
+| Filesystem | | Built-in | Built-in
|
+| Apache Kafka | 0.8 | `flink-connector-kafka-0.8` | Not
available |
+| Apache Kafka | 0.9 | `flink-connector-kafka-0.9` |
[Download](http://central.maven.org/maven2/org/apache/flink/flink-connector-kafka-0.9{{site.scala_version_suffix}}/{{site.version}}/flink-connector-kafka-0.9{{site.scala_version_suffix}}-{{site.version}}-sql-jar.jar)
|
+| Apache Kafka | 0.10 | `flink-connector-kafka-0.10` |
[Download](http://central.maven.org/maven2/org/apache/flink/flink-connector-kafka-0.10{{site.scala_version_suffix}}/{{site.version}}/flink-connector-kafka-0.10{{site.scala_version_suffix}}-{{site.version}}-sql-jar.jar)
|
+| Apache Kafka | 0.11 | `flink-connector-kafka-0.11` |
[Download](http://central.maven.org/maven2/org/apache/flink/flink-connector-kafka-0.11{{site.scala_version_suffix}}/{{site.version}}/flink-connector-kafka-0.11{{site.scala_version_suffix}}-{{site.version}}-sql-jar.jar)
|
+
+### Formats
+
+| Name | Maven dependency | SQL Client JAR |
+| :---------------- | :--------------------------- | :--------------------- |
+| CSV | Built-in | Built-in |
+| JSON | `flink-json` |
[Download](http://central.maven.org/maven2/org/apache/flink/flink-json/{{site.version}}/flink-json-{{site.version}}-sql-jar.jar)
|
+| Apache Avro | `flink-avro` |
[Download](http://central.maven.org/maven2/org/apache/flink/flink-avro/{{site.version}}/flink-avro-{{site.version}}-sql-jar.jar)
|
+
+{% else %}
+
+This table is only available for stable releases.
+
+{% endif %}
+
+{% top %}
+
+Overview
+--------
+
+Beginning from Flink 1.6, the declaration of a connection to an external
system is separated from the actual implementation. Connections can be
specified either
+
+- **programmatically** using a `Descriptor` under
`org.apache.flink.table.descriptors` for Table & SQL API
+- or **declaratively** via [YAML configuration files](http://yaml.org/) for
the SQL Client.
+
+This allows not only for better unification of APIs and SQL Client but also
for better extensibility in case of [custom implementations](sourceSinks.html)
without changing the declaration.
+
+Similar to a SQL `CREATE TABLE` statement, one can define the name of the
table, the final schema of the table, connector, and a data format upfront for
connecting to an external system. Additionally, the table's type (source, sink,
or both) and an update mode for streaming queries can be specified:
+
+<div class="codetabs" markdown="1">
+<div data-lang="Java/Scala" markdown="1">
+{% highlight java %}
+tableEnvironment
+ .connect(...)
+ .withFormat(...)
+ .withSchema(...)
+ .inAppendMode()
+ .registerTableSource(...)
+{% endhighlight %}
+</div>
+
+<div data-lang="YAML" markdown="1">
+{% highlight yaml %}
+name: MyTable
+type: source
+update-mode: append
+schema: ...
+format: ...
+connector: ...
+{% endhighlight %}
+</div>
+</div>
+
+The subsequent sections will cover each definition part
([schema](connect.html#table-schema),
[connector](connect.html#table-connectors),
[format](connect.html#table-formats), and [update
mode](connect.html#update-modes)) in more detail.
+
+The following code shows a full example of how to connect to Kafka for reading
Avro records.
+
+<div class="codetabs" markdown="1">
+<div data-lang="Java/Scala" markdown="1">
+{% highlight java %}
+tableEnvironment
+ // declare the external system to connect to
+ .connect(
+ new Kafka()
+ .version("0.10")
+ .topic("test-input")
+ .startFromEarliest()
+ .property("zookeeper.connect", "localhost:2181")
+ .property("bootstrap.servers", "localhost:9092")
+ )
+
+ // declare a format for this system
+ .withFormat(
+ new Avro()
+ .avroSchema(
+ "{" +
+ " \"namespace\": \"org.myorganization\"," +
+ " \"type\": \"record\"," +
+ " \"name\": \"UserMessage\"," +
+ " \"fields\": [" +
+ " {\"name\": \"timestamp\", \"type\": \"string\"}," +
+ " {\"name\": \"user\", \"type\": \"long\"}," +
+ " {\"name\": \"message\", \"type\": [\"string\", \"null\"]}" +
+ " ]" +
+ "}" +
+ )
+ )
+
+ // declare the final schema of the table
+ .withSchema(
+ new Schema()
+ .field("rowtime", Types.SQL_TIMESTAMP)
+ .rowtime(new Rowtime()
+ .timestampsFromField("ts")
+ .watermarksPeriodicBounded(60000)
+ )
+ .field("user", Types.LONG)
+ .field("message", Types.STRING)
+ )
+
+ // specify the update-mode for streaming tables
+ .inAppendMode()
+
+ // register as source, sink, or both and under a name
+ .registerTableSource("MyUserTable");
+{% endhighlight %}
+</div>
+
+<div data-lang="YAML" markdown="1">
+{% highlight yaml %}
+tables:
+ - name: MyUserTable # name the new table
+ type: source # declare if the table should be "source", "sink",
or "both"
+ update-mode: append # specify the update-mode for streaming tables
+
+ # declare the final schema of the table
+ schema:
+ - name: rowtime
+ type: TIMESTAMP
+ rowtime:
+ timestamps:
+ type: from-field
+ from: ts
+ watermarks:
+ type: periodic-bounded
+ delay: "60000"
+ - name: user
+ type: BIGINT
+ - name: message
+ type: VARCHAR
+
+ # declare a format for this system
+ format:
+ type: avro
+ avro-schema: >
+ {
+ "namespace": "org.myorganization",
+ "type": "record",
+ "name": "UserMessage",
+ "fields": [
+ {"name": "ts", "type": "string"},
+ {"name": "user", "type": "long"},
+ {"name": "message", "type": ["string", "null"]}
+ ]
+ }
+
+ # declare the external system to connect to
+ connector:
+ type: kafka
+ version: "0.10"
+ topic: test-input
+ startup-mode: earliest-offset
+ properties:
+ - key: zookeeper.connect
+ value: localhost:2181
+ - key: bootstrap.servers
+ value: localhost:9092
+{% endhighlight %}
+</div>
+</div>
+
+In both ways the desired connection properties are converted into normalized,
string-based key-value pairs. So-called [table
factories](sourceSinks.html#define-a-tablefactory) create configured table
sources, table sinks, and corresponding formats from the key-value pairs. All
table factories that can be found via Java's [Service Provider Interfaces
(SPI)](https://docs.oracle.com/javase/tutorial/sound/SPI-intro.html) are taken
into when searching for exactly-one matching table factory.
+
+If no factory can be found or multiple factories match for the given
properties, an exception will be thrown with additional information about
considered factories and supported properties.
+
+Table Schema
+------------
+
+The table schema allows for describing the final appearance of a table. It
specifies the final name, final type, and the origin of a field. The origin of
a field might be important if the name of the field should differ from the
input/output format. For instance, a field `name&field` should reference
`nameField` from an Avro format. Additionally, the schema is needed to map
column names and types from an external system to Flink's representation. In
case of a table sink, it ensures that only data with valid schema is written to
an external system.
Review comment:
How about describing it as follows:
> The table schema descriptor defines the schema of a table as it is exposed
to SQL and Table API queries. Moreover, it defines for a source connector how
the table schema is derived from the storage format and for a sink connector
how the storage format is derived from the table schema, i.e., defining the
bridge between between a logical table and the physical format representation.
- "allows for describing" sounds optional but the schema must always be
defined.
- I would remove `final` from name and type. What would be the non-final
name and type of a field?
- I think the example of `name&field` confusing because the name of the
field contains `field`.
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> Document unified table sources/sinks/formats
> --------------------------------------------
>
> Key: FLINK-9947
> URL: https://issues.apache.org/jira/browse/FLINK-9947
> Project: Flink
> Issue Type: Improvement
> Components: Documentation, Table API & SQL
> Reporter: Timo Walther
> Assignee: Timo Walther
> Priority: Major
> Labels: pull-request-available
>
> The recent unification of table sources/sinks/formats needs documentation. I
> propose a new page that explains the built-in sources, sinks, and formats as
> well as a page for customization of public interfaces.
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