ATLAS-2687: Create twiki documentation about classification propagation

docs/src/site/twiki/ClassificationPropagation.twiki

+---+ Classification Propagation
+
+Classification propagation enables classifications associated to an entity to be automatically associated with other
+related entities of the entity. This is very useful in dealing with scenarios where a dataset derives it data from other
+datasets - like a table loaded with data in a file, a report generated from a table/view, etc. For example, when a table
+is classified as *"PII"*, tables or views that derive data from this table (via CTAS or ‘create view’ operation) will be
+automatically classified as *"PII"*.
+
+
+---++ Use Cases
+Consider the following lineage where data from a 'hdfs_path' entity is loaded into a table, which is further made
+available through views. We will go through various scenarios to understand the classification propagation feature.
+
+<img src="images/twiki/classification-propagation-1.png"/>
+
+
+---++ Add classification to an entity
+When classification ‘PII’ is added to 'hdfs_path' entity, the classification is propagated to all impacted entities in the
+lineage path, including 'employees' table, views 'us_employees' and 'uk_employees' - as shown below.
+
+<img src="images/twiki/classification-propagation-2.png"/>
+
+---++ Update classification associated with an entity
+Any updates to classifications associated with an entity will be seen in all entities the classification is
+propagated to as well.
+
+<img src="images/twiki/classification-propagation-3.png"/>
+
+---++ Remove classification associated with an entity
+When a classification is deleted from an entity, the classification will be removed from all entities the classification
+is propagated to as well.
+
+<img src="images/twiki/classification-propagation-4.png"/>
+
+---++ Add lineage between entities
+When lineage is added between entities, for example to capture loading of data in a file to a table, the classifications
+associated with the source entity are propagated to all impacted entities as well.
+
+For example, when a view is created from a table, classifications associated with the table are propagated to the newly
+created view as well.
+
+<img src="images/twiki/classification-propagation-5.png"/>
+
+---++ Delete an entity
+When an entity is deleted, classifications associated with this entity will be removed from all entities the
+classifications are propagated to.
+
+For example. when _employees_ table is deleted, classifications associated with this table are removed from
+'employees_view' view.
+
+<img src="images/twiki/classification-propagation-6.png"/>
+
+---++ Control Propagation
+Apache Atlas provides few options to control whether/where a classification is propagated.
+This section details available options.
+
+---++ Propagate flag in classification
+Each association of classification to an entity has a boolean flag that controls whether the classification is
+propagated or not. When a classification is associated with an entity, this flag is set to ‘true’ i.e. the classification
+will be propagated to all impacted entities. This flag can be updated to desired value during initial association or later.
+
+<img src="images/twiki/classification-propagation-7.png"/>
+
+---++ Propagate flag in lineage edge
+Apache Atlas supports a flag at lineage edge to enable/disable propagation of classifications through the edge. By default,
+the propagation is enabled for lineage edges. When the flag is turned off, no classification will be propagated through
+this edge; and propagation of currently propagated classifications through the edge will be reevaluated, so that they can
+be removed from impacted entities. When the flag is turned on, propagation of classifications of the source entity will
+be reevaluated, so that they can be propagated to all impacted entities.
+
+---++ Block propagation of specific classifications in lineage edge
+Apache Atlas supports blocking propagation of specific classifications in at lineage edges. This can be useful, for example,
+to handle scenarios like: a column classified as PII is masked when creating a view; in such scenario, if corresponding
+column in the created view might not have PII, hence the propagation of PII classification should be blocked. This can be
+done by updating the lineage edge to add the PII classification in _‘blocked propagated classifications’_ list.
+Classifications in blocked propagated classifications will not be propagated in the derivative/downstream entities.
+
+<img src="images/twiki/classification-propagation-8.png"/>
+
+---++ Notifications and Audit
+When propagated classifications are added/update/deleted, Apache Atlas sends notifications to 'ATLAS_ENTITIES' topic for
+each entity affected by the propagation.
+
+---++ Glossary
+When a classification is associated with a glossary term, the classification is automatically propagated to all entities
+associated with the term.
\ No newline at end of file

docs/src/site/twiki/index.twiki

@@ -58,6 +58,7 @@ capabilities around these data assets for data scientists, analysts and the data
    * [[Atlas-Authentication][Authentication]]
    * [[Atlas-Authorization-Model][Atlas Authorization Model]]
       * [[Configure-simple-authorizer][Steps to configure Atlas Simple Authorizer]]
+   * [[ClassificationPropagation][Classification Propagation]]
    * [[Configuration][Configuration]]
    * [[Notifications][Notifications]]
    * Hooks & Bridges