bowenli86 commented on a change in pull request #9308:
[FLINK-13517][docs][hive] Restructure Hive Catalog documentation
URL: https://github.com/apache/flink/pull/9308#discussion_r311786181
##########
File path: docs/dev/table/catalog.md
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@@ -23,344 +23,151 @@ specific language governing permissions and limitations
under the License.
-->
-Catalogs provide metadata, such as names, schemas, statistics of tables, and
information about how to access data stored in a database or other external
systems. Once a catalog is registered within a `TableEnvironment`, all its
meta-objects are accessible from the Table API and SQL queries.
+Catalogs provide metadata, such as names, schemas, table statistics, and
information needed to access data stored in a database or other external
systems.
+One of the most crucial aspects of data processing is managing metadata. It
may be transient metadata like temporary tables, or UDF's registered against
the table environment. Or permanent metadata, like a Hive Metastore. Catalogs
provide a unified API for managing metadata and making it accessible from the
Table API and SQL Queries.
* This will be replaced by the TOC
{:toc}
+## Catalog Types
-Catalog Interface
------------------
+### GenericInMemoryCatalog
-APIs are defined in `Catalog` interface. The interface defines a set of APIs
to read and write catalog meta-objects such as database, tables, partitions,
views, and functions.
+Flink sessions always have a built-in `GenericInMemoryCatalog` named
`default_catalog`, which has a built-in default database named
`default_database`. All temporary metadata, such tables defined using
`TableEnvironment#registerTable` is registered to this catalog.
+### HiveCatalog
-Catalog Meta-Objects Naming Structure
--------------------------------------
+The `HiveCatalog` serves two purposes; as persistent storage for pure Flink
metadata, and as an interface for reading and writing Hive tables. The Flink's
[Hive documentation]({{ site.baseurl }}/dev/table/hive/index.html) provides
full details on setting up the catalog and interfacing with an existing Hive
installation.
Review comment:
```suggestion
The `HiveCatalog` serves two purposes; as persistent storage for pure Flink
metadata, and as an interface for reading and writing existing Hive metadata.
The Flink's [Hive documentation]({{ site.baseurl }}/dev/table/hive/index.html)
provides full details on setting up the catalog and interfacing with an
existing Hive installation.
```
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