Does ODL support the use of the <abstract> keyword to declare abstract classes (interfaces) and to mark operations as abstract, indicating they have no implementation at that level?

Introduction / Context:
Abstraction is a cornerstone of object modeling. Declaring a class or an operation as abstract signals that it captures common behavior or contracts but is not directly instantiable or implemented at that level. ODL, designed to mirror familiar OO constructs for object databases, includes support for abstract declarations to improve schema expressiveness and reuse.

Given Data / Assumptions:

• We are defining object schemas that may rely on inheritance polymorphism.
• Some interfaces should not be instantiated directly but should be specialized.
• Some operations are defined only as contracts to be implemented by subtypes.

Concept / Approach:
Using the abstract modifier on classes (interfaces) communicates “no direct instances,” guiding both developer expectations and tooling. Marking operations as abstract conveys that subclasses must supply implementations. These declarations parallel mainstream languages and fit naturally in ODL, which focuses on structural declarations while delegating implementation to language bindings.

Step-by-Step Solution:
Identify shared structure/behavior across several concrete classes.Create an abstract base in ODL to hold common attributes/relationships/operation signatures.Declare operations abstract where behavior is deferred to subtypes.Have concrete subclasses specialize and implement those operations.Ensure queries and relationships target supertypes when appropriate to leverage polymorphism.

Verification / Alternative check:
Inspect ODL examples from standard texts; abstract declarations appear on both classes and operations to support inheritance hierarchies without forcing direct instantiation.

Why Other Options Are Wrong:
Option b ignores ODL’s OO alignment. Options c and d artificially restrict abstract usage. Option e invents an unrelated transient-only limitation.

Common Pitfalls:
Creating deep hierarchies that complicate querying; forgetting to implement abstract operations in concrete subclasses; mixing abstract declarations with persistence rules without documenting instantiation policies.

Final Answer:
Applies — ODL supports abstract classes and abstract operations