Difficulty: Easy
Correct Answer: All of the above types of collections can be produced depending on the OQL query written
Explanation:
Introduction / Context:
This question examines Object Query Language OQL, which is used to retrieve and manipulate objects in object oriented database systems. OQL is conceptually similar to SQL but operates on collections of objects and their attributes. It supports returning entire collections, filtered subsets, and results with or without duplicate elimination. Understanding the flexibility of OQL in constructing different types of result sets is important for designing object oriented queries.
Given Data / Assumptions:
Concept / Approach:
Object Query Language is designed to handle complex collections of objects. It allows queries that project and select attributes, join collections, and perform aggregations. Similar to SQL, OQL can return full collections of objects, apply a distinct like operation to remove duplicates, or restrict results with where like clauses. Therefore, options that describe these different types of collections are not mutually exclusive. The correct answer must recognize that OQL is capable of returning all of these result types depending on the query that is written.
Step-by-Step Solution:
Step 1: Recall that OQL can return full collections from classes or relationships without necessarily eliminating duplicates.Step 2: Recognize that OQL, like SQL, can support operations that remove duplicate values, resulting in a distinct collection.Step 3: Observe that OQL supports selection predicates, allowing the query to return only those objects that match specified criteria.Step 4: Notice that no rule limits OQL to only one type of result set; it can produce many forms based on query structure.Step 5: Conclude that the option stating all of the listed result types can be produced is the correct one.
Verification / Alternative check:
Examining examples of OQL usage shows queries that return entire collections of objects representing all instances of a particular class. Other examples show filters based on attribute values, which produce subsets of the original collections. Documentation and tutorials also demonstrate how to eliminate duplicates in OQL results, much like DISTINCT in SQL. These examples confirm that OQL is not restricted to scalar results nor to a single type of collection, but can generate all of the described result types.
Why Other Options Are Wrong:
The option stating that OQL can only return a complete collection including duplicates is incomplete, because OQL also allows filters and duplicate removal. The option that focuses solely on collections without duplicates does not account for cases where duplicates are desired or unavoidable. The option that mentions only specific subsets also fails to acknowledge that full collections and duplicate inclusive results are possible. The statement that OQL can return only a single scalar value is clearly incorrect, since OQL is designed to return collections of objects as well as aggregates.
Common Pitfalls:
A common mistake is to assume that object oriented query languages are more limited than SQL, perhaps returning only object references or only scalar aggregates. In reality, OQL is quite expressive and mirrors many capabilities of SQL, including returning full collections, distinct sets, and filtered subsets. To avoid confusion, students should consider OQL as a general purpose query language for objects, not merely a special tool for one type of result.
Final Answer:
OQL can produce all of the above types of collections, including full collections, collections without duplicates, and filtered subsets, depending on the query written.
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