# Extensibility Overview
With the Extensibility apps, you can create custom fields, data source extensions, and implementation descriptions for specific business contexts to enhance pre- delivered applications that are extensible to adapt them to your business needs.
You can also create custom CDS views based on pre- delivered data sources. The data of an application is distributed across several database tables. Using CDS views, you can merge the data from different data sources and rearrange the table fields according to application-specific needs.
You can create custom business objects with UIs. You can also add custom logic to custom business objects. You can thus create your own applications based on custom business objects.
You can use Custom Analytical Queries to create new queries or reuse predefined queries. You use fields from CDS views to create a query.
Extension items can be transported with the apps Export Software Collection and Import Software Collection to be productively available und usable.
Nate: You can extend applications and their UIs, reports, email templates, and form templates only if the applications that you want to extend are extensible.
# How to Check if Fiori App is extensible or not
Go to Fiori App Library (https://fioriappslibrary.hana.ondemand.com/sap/fix/externalViewer/)
And check if ‘Create Customer Project’ App is extensible or not. We would use ‘Create Customer Project’ App for our example for this article.
This app is extensible
# Add custom field in Create Customer Project App
We would add a field (Project Type field drop down values) in app ‘Create Customer Project’.
Business Unit: Mining
Step 1: Go to ‘Custom Fields and Logic’ App
Note: You need to select right Business Context from drop down
Click Create & Edit
Enable wherever field is required, also make it searchable
Got Published (Field is available to be consumed)
Step 2: Go to ‘Create Customer Project’ App
Now you need to add that field which we created in previous step.
Click User Icon
Click Adapt UI
Right Click on the page and Click Create Group
Name This group as "Customer Specific Fields"
Right Click on Customer Specific Fields and you would get options – Select Add Fields
Search your fields i.e. Business Unit
Select and click OK
Click Publish and then Save Exit
Now the field is available in ‘Create Customer Project’ App with drop down options
Step 3: Go to ‘Create Customer Project’ App and create project with using custom added field
Similarly, you need to add this field in Plan Customer Project App so see these fields there.
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