For configuration data that is read frequently but updated infrequently, a transparent table is the standard and correct persistence choice. It allows for efficient reads via standard SQL and is fully supported within the ABAP Cloud development model. BOPF is for transactional business objects, temporary tables are for session-specific data, and stored procedures are not the primary persistence mechanism in ABAP Cloud.

To expose a field from an extension business object to a Fiori UI, it must be added to the projection view layer. Specifically, you add the field to the extension include (`EXTENSION_*`) of the relevant standard projection view. This is the sanctioned way to make custom fields available to the UI without modifying standard SAP artifacts.

The most aligned approach with SAP Fiori and the separation of concerns in RAP is to use UI annotations with conditional expressions. The `@UI.hidden` annotation can use `$user.` or other path expressions to dynamically show, hide, or make fields read-only based on user context or other data, keeping the control in the metadata layer rather than hard-coded ABAP logic.

For replicating large volumes of data efficiently for analytical or read-only purposes in a side-by-side extension, the recommended method is to use Analytical CDS Views exposed via the OData Protocol for Data (ODP). This framework is optimized for data extraction and replication, unlike transactional OData APIs or RFCs which are better for transactional or smaller-scale operational calls.

In a managed RAP scenario, validations on the root entity are triggered for each operation on an instance (e.g., multiple line item changes). To optimize, a common pattern is to use a transient helper field (e.g., `validation_flag`) that is set in a determination. The `validateSave` then checks this flag and only executes the expensive logic if it’s set, clearing it afterwards to prevent redundant executions in the same save sequence.

Key user fields are stored in separate extension tables (e.g., `ISALESDOCUMENT_I_INAC`). To use them in a developer extension, you must explicitly read from this database table extension using the appropriate key (e.g., the sales order document number and item). They are not automatically part of the standard BO’s data model exposed for developer use unless explicitly included via other means.

In a RAP action implementation (especially in a managed scenario), you must explicitly inform the framework that data has been modified to trigger the subsequent save sequence. This is done by setting the `CHANGED` system variable to `ABAP_TRUE` within the action’s method. Without this, the framework assumes the action was read-only.

In the ABAP Cloud model, data access control is enforced at the database layer using Core Data Services Access Control (DCL). A DCL defines roles and conditions (e.g., `WHERE CompanyCode = $session.user_company_code`) that are automatically applied whenever the associated CDS view is accessed. This is the mandatory and most secure way to implement field-, row-, or column-level protection.

Draft isolation is enforced by the RAP framework’s draft lock mechanism. When a user creates or edits a draft, a lock is placed on the active instance (or on the draft itself for new instances). This lock is user-specific and prevents other users from editing the same draft or the underlying active object until the draft is activated or discarded, ensuring data consistency.

For configuration data that is read frequently but updated infrequently, a transparent table is the standard and correct persistence choice. It allows for efficient reads via standard SQL and is fully supported within the ABAP Cloud development model. BOPF is for transactional business objects, temporary tables are for session-specific data, and stored procedures are not the primary persistence mechanism in ABAP Cloud.0