Mystery of Net Service Topology Model in Oracle Apps/EBS R12

The Net Services Topology Data Model stores the entire topological information about a single Oracle E-Business Suite instance. The data model stores information about each node in the Oracle E-Business Suite instance, which is then used to generate Net Service configuration files such as tnsnames.ora.
The Net Services Topology Data Model stores the following information:

• Database tier: Hostname, Database SID, Database Name, Instance Name, TNS Descriptors
• Application tier: Hostname, FNDFS and FNDSM alias descriptors

So, whenever one runs AutoConfig on respective tier (DB or Apps), it automatically seeds the data model with relevant data. When runs,  AutoConfig automatically runs adgentns.pl, which is responsible for creating net services topology information. 


There is one more thing, usually causes the confusion i.e. when to de-register the DB or Apps tier from Net Services Topology Model.
Answer is based on, which tier you are speaking of.
for Apps tier - Whenever one deletes the apps tier/node
for DB Tier - Whenever the DB Host Name, Port, SID or DB Name is changed.


-- To de-register the Apps tier - 
#perl <AD_TOP>/bin/adgentns.pl contextfile=<CONTEXT_FILE> -removeserver


To de-register DB Tier - 
#perl <RDBMS ORACLE_HOME>/appsutil/bin/adgentns.pl contextfile=<CONTEXT_FILE> -removeserver


Sometimes one also needs to purge entire data mode and recreate it. Hence one can purge entire data model as follows.
#perl <AD_TOP>/bin/adgentns.pl contextfile=<CONTEXT_FILE> -removesystem

-- This will clean up the information in fnd_app_servers and fnd_nodes table.


After purging, to repopulate the data model, run AutoConfig on respective tier (DB or Apps), it automatically seeds the data model with relevant data.