Object Databases — Meaning of an 'Extent' In object database terminology, what does the term extent refer to within a database?

Introduction:
In object-oriented database management systems (OODBMS), terminology mirrors object-oriented programming while adding persistence concepts. One foundational term is extent. Recognizing what an extent represents helps bridge conceptual class modeling and actual stored objects in the database.

Given Data / Assumptions:

• The context is an object database, not purely a relational system.
• Classes define types; objects are instances persisted by the OODBMS.
• We want the precise definition of extent in this setting.

Concept / Approach:
An extent is the collection of all persistent objects (instances) of a given class (and sometimes its subclasses, depending on the ODBMS) stored in the database. It is the object database analogue of a table in relational systems, but oriented around object identity and class membership rather than rows in a relation defined by columns.

Step-by-Step Solution:
1) Identify that classes have many objects in persistent storage.2) Recognize that the system groups these object instances for management and query.3) The grouped set is called the extent of that class.4) Therefore, extent = set of all instances of a class in the database.

Verification / Alternative check:
Check OODBMS documentation (e.g., ODMG/ODL contexts): extents are explicitly defined to enumerate and query over all objects of a class. Query languages may iterate across a class extent similarly to scanning a table in SQL.

Why Other Options Are Wrong:

• Inheritance keywords (a, b): Extent does not define inheritance direction; extends/implements do.
• Single instance (d): Extent is a set, not one instance.
• Physical file segment (e): That is storage-engine terminology in some RDBMSs, unrelated to OODBMS extent semantics.

Common Pitfalls:
Equating class extent with a single object, or confusing OODBMS terms with physical storage terms from relational systems. Always distinguish logical object collections from low-level files or pages.

Final Answer:
The set of all instances of a class within a database