How to install Oracle Client in order to create an ArcGIS connection with an enterprise database.

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Depending on your business scenario, a regular geodatabase might not be enough to be used along with your ArcGIS. For example, in order to use some of Maximo Spatial's functionalities, a Feature Service must be configured in your published Map Service. To have a Feature Service configured, only a normal .gdb database will not be enough. You will have to install one of the supported enterprise databases (such as SQL Server, Oracle, et cetera) and configure it as a Data Store, which will have to be connected with your ArcGIS. Please notice that this document will only describe the process for Oracle databases.

Steps:

1. Download (both can be found at Oracle's website):
    -Instant Client Package - Basic
    -Instant Client Package - ODBC
*Please make sure that the client and ArcMap are both 32-bit or 64-bit.
2. Unzip the content of both files into the same folder and rename it to oracle_odbc.
3. Move the folder to the root of you C:\ directory.
4. Open the Control Panel and click System Info.
5. Click Advanced system settings.
6. Click Environment Variables inside the Advanced tab.
7. Click New... under System variables (not the one under User variables for Administrator).
8. Inside Variable name, type: "TNS_ADMIN".
9. Inside Variable value, type the directory where our instant client is. In this case, it's "C:\oracle_odbc".
10. Edit the Path variable and add ";C:\oracle_odbc" to the end of its value field (DON'T erase anything, just add the directory to the end of the string).
11. Go to the instant client folder and run "odbc_install.exe" as administrator (right click, then "Run as administrator").
12. Create a .txt file.
13. Open it and paste the following content into it:

<addressname> = (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(Host = <hostname>)(Port = <port>)) ) (CONNECT_DATA = (SERVICE_NAME = <service_name>) ) )?

14. Replace the tags (such as "<port>") for the values that match with the machine's info (e.g. "<hostname>" for "000.000.0.000"). You can name <addressname> however you like.
15. Rename the txt file as "tnsnames" and change its extension to ".ora".
16. Restart your machine if needed.

Done! Now you should be able to create your database connection in ArcMap without any issue.