We consider Orbeon PE 4.10 for one of our projects. I know that you can add custom form elements as XBL components. Therefore, I read this documentation.
For our project, we need to add datamodel elements to the Form Builder (like the creation of an Microsoft Access form for an existing Access datamodel). Let´s say we have an existing database datamodel with an entity event. This entity has e.g. 15 database attributes like an arrival date, expected number of participants, topic, description etc.
When I create a new form for an event in Form Builder, I want to see all the fields mentioned above in a tree structure so that users can drag and drop those fields into a form (exactly like in Access). In addition, there should be a data binding between the form elements and the database entity.
My question is, of this is possible to realize without changing the source code of orbeon forms PE?
Orbeon Forms doesn't do "relational database mapping", but instead focuses on data capture. So the approach is maybe a little bit different than what you would do in Access. Instead of starting with a database schema, and then designing a form that you map to that schema, you start with the form, and Form Builder automatically creates an XML document for you that holds the data entered by users, and that XML document is typically stored as-is in your database. Then, when you need to access the data, you have Orbeon Forms send the XML to your app, go through the REST API, or access the XML directly in the database.
Now, about the event use case you're describing, if this is something that happens in several forms, you can create a section template for that event, and reuse it whereever you need it. For cases where you need something more custom, like a special date field, map field, or special type of number that requires a custom validation, you can create your own XBL component, which gives you more control, but requires a little more work to put in place compared to section templates.