The expression itab1 = corresponding #( itab2 ) is a constructor expression with the component operator CORRESPONDING that assigns the contents of the internal table itab2 to the internal table itab1. The following statements are true for using this expression:
* B: itab1 and itab2 must have at least one field name in common. This is because the component operator CORRESPONDING assigns the identically named columns of itab2 to the identically named columns of itab1 by default, according to the rules of MOVE-CORRESPONDING for internal tables. If itab1 and itab2 do not have any field name in common, the expression will not assign any value to itab1 and it will remain initial or unchanged1
* C: Fields with the same name and the same type will be copied from itab2 to itab1. This is because the component operator CORRESPONDING assigns the identically named columns of itab2 to the identically named columns of itab1 by default, according to the rules of MOVE-CORRESPONDING for
* internal tables. If the columns have the same name but different types, the assignment will try to perform a conversion between the types, which may result in a loss of precision, a truncation, or a runtime error, depending on the types involved1 The following statements are false for using this expression:
* A: Fields with the same name but with different types may be copied from itab2 to itab1. This is not true, as explained in statement C. The assignment will try to perform a conversion between the types, which may result in a loss of precision, a truncation, or a runtime error, depending on the types involved1
* D: itab1 and itab2 must have the same data type. This is not true, as the component operator CORRESPONDING can assign the contents of an internal table of one type to another internal table of a different type, as long as they have at least one field name in common. The target type of the expression is determined by the left-hand side of the assignment, which is itab1 in this case. The expression will create an internal table of the same type as itab1 and assign it to itab11 References: CORRESPONDING - Component Operator - ABAP Keyword Documentation

The following are the explanations for each statement:
* A: This statement is correct. go_subl = CAST #(go_super) will not work. This is because go_subl is a data object of type REF TO cl_subl, which is a reference to the subclass cl_subl. go_super is a data object of type REF TO cl_super, which is a reference to the superclass cl_super. The CAST operator is used to perform a downcast or an upcast of a reference variable to another reference variable of a compatible type. A downcast is a conversion from a more general type to a more specific type, while an upcast is a conversion from a more specific type to a more general type. In this case, the CAST operator is trying to perform a downcast from go_super to go_subl, but this is not possible, as go_super is not pointing to an instance of cl_subl, but to an instance of cl_super. Therefore, the CAST operator will raise an exception CX_SY_MOVE_CAST_ERROR at runtime12
* B: This statement is incorrect. go_sub2 = CAST #(go_super) will work. go_subl = CAST #(go_super) will not work. This is because go_sub2 is a data object of type REF TO cl_sub2, which is a reference to the subclass cl_sub2. go_super is a data object of type REF TO cl_super, which is a reference to the superclass cl_super. The CAST operator is used to perform a downcast or an upcast of a reference variable to another reference variable of a compatible type. A downcast is a conversion from a more general type to a more specific type, while an upcast is a conversion from a more specific type to a more general type. In this case, the CAST operator is trying to perform a downcast from go_super to go_sub2, and this is possible, as go_super is pointing to an instance of cl_sub2, which is a subclass of cl_super.
* Therefore, the CAST operator will assign the reference of go_super to go_sub2 without raising an exception. However, the CAST operator will not work for go_subl, as explained in statement A12
* C: This statement is incorrect. go_sub2 = CAST #(go_super) will work. go_sub2->sub2_meth1(...) will not work. This is because go_sub2 is a data object of type REF TO cl_sub2, which is a reference to the subclass cl_sub2. go_super is a data object of type REF TO cl_super, which is a reference to the superclass cl_super. The CAST operator is used to perform a downcast or an upcast of a reference variable to another reference variable of a compatible type. A downcast is a conversion from a more general type to a more specific type, while an upcast is a conversion from a more specific type to a more general type. In this case, the CAST operator is trying to perform a downcast from go_super to go_sub2, and this is possible, as go_super is pointing to an instance of cl_sub2, which is a subclass of cl_super.
Therefore, the CAST operator will assign the reference of go_super to go_sub2 without raising an exception. However, the method call go_sub2->sub2_meth1(...) will not work, as sub2_meth1 is a subclass-specific method of cl_sub2, which is not inherited by cl_super. Therefore, the method call will raise an exception CX_SY_DYN_CALL_ILLEGAL_METHOD at runtime123
* D: This statement is correct. go_subl->subl_meth1(...) will work. This is because go_subl is a data object of type REF TO cl_subl, which is a reference to the subclass cl_subl. subl_meth1 is a subclass-specific method of cl_subl, which is not inherited by cl_super. Therefore, the method call go_subl->subl_meth1(...) will work, as go_subl is pointing to an instance of cl_subl, which has the method subl_meth1123 References: NEW - ABAP Keyword Documentation, CAST - ABAP Keyword Documentation, Method Call - ABAP Keyword Documentation

The order in which objects are created to generate a RESTful Application Programming application is A, D, C, B. This means that the following steps are followed:
* First, a database table is created to store the data for the application. A database table is a CDS DDIC-based view that defines a join or union of database tables. A database table has an SQL view attached and can be accessed by Open SQL or native SQL.
* Second, a data model view is created to define a data model based on the database table or other CDS view entities. A data model view is a CDS view entity that can have associations, aggregations, filters, parameters, and annotations. A data model view can also define the behavior definition and implementation for the business object.
* Third, a service definition is created to define the service interface for the application. A service definition is a CDS view entity that defines a projection on a data model view or another service definition. A service definition can also define service metadata, such as service name, version, description, and annotations.
* Fourth, a service binding is created to define the service binding for the application. A service binding is a CDS view entity that defines a projection on a service definition. A service binding can also define the service protocol, such as OData V2, OData V4, or REST, and the service URL.
References: CDS Data Model Views - ABAP Keyword Documentation, CDS Service Definitions - ABAP Keyword Documentation, CDS Service Bindings - ABAP Keyword Documentation, CDS Projection Views - ABAP Keyword Documentation

The object that can be used to set a field to read-only in all applications of the RESTful Application Programming model (RAP) is the behaviour definition. The behaviour definition is a CDS artefact that defines the business logic and the UI behaviour of a business object. A business object is a CDS entity that represents a business entity or concept, such as a customer, an order, or a product. The behaviour definition can specify the properties of the fields of a business object, such as whether they are mandatory, read-only, or transient. These properties are valid for all applications that use the business object, such as transactional, analytical, or draft-enabled apps12. For example:
* The following code snippet defines a behaviour definition for a business object ZI_PB_APPLICATION.
It sets the field APPLICATION to read-only for all applications that use this business object:
define behavior for ZI_PB_APPLICATION { field ( read only ) APPLICATION; ... } You cannot do any of the following:
* A. Service definition: A service definition is a CDS artefact that defines the interface and the binding of a service. A service is a CDS entity that exposes the data and the functionality of one or more business objects as OData, InA, or SQL services. A service definition can specify the properties of the fields of a service, such as whether they are filterable, sortable, or aggregatable. However, these properties are only valid for the specific service that uses the business object, not for all applications that use the business object12.
* C. Projection view: A projection view is a CDS artefact that defines a view on one or more data sources, such as tables, views, or associations. A projection view can select, rename, or aggregate the fields of the data sources, but it cannot change the properties of the fields, such as whether they are read-only or not. The properties of the fields are inherited from the data sources or the behaviour definitions of the business objects12.
* D. Metadata extension: A metadata extension is a CDS artefact that defines additional annotations for a CDS entity, such as a business object, a service, or a projection view. A metadata extension can specify the properties of the fields of a CDS entity for UI or analytical purposes, such as whether they are visible, editable, or hidden. However, these properties are only valid for the specific UI or analytical application that uses the metadata extension, not for all applications that use the CDS entity12.
References: 1: ABAP CDS - Data Definitions - ABAP Keyword Documentation - SAP Online Help 2: ABAP CDS - Behavior Definitions - ABAP Keyword Documentation - SAP Online Help

The nested join is evaluated from the top to the bottom in the order of the ON conditions. This means that the join expression is formed by assigning each ON condition to the directly preceding JOIN from left to right.
The join expression can be parenthesized implicitly or explicitly to show the order of evaluation. In this case, the implicit parentheses are as follows:
SELECT * FROM (a INNER JOIN (b INNER JOIN c ON b~c = c~c) ON a~b = b~b) This means that the first join expression is b INNER JOIN c ON b~c = c~c, which joins the columns of tables b and c based on the condition that b~c equals c~c. The second join expression is a INNER JOIN (b INNER JOIN c ON b~c = c~c) ON a~b = b~b, which joins the columns of table a and the result of the first join expression based on the condition that a~b equals b~b. The final result set contains all combinations of rows from tables a, b, and c that satisfy both join conditions.
References: 1: SELECT, FROM JOIN - ABAP Keyword Documentation - SAP Online Help