Question 1

In Object Database Language (ODL) modeling for object-oriented databases, the keyword “inverse” is used to declare the bidirectional counterpart of what construct? Provide the most precise ODL concept referenced by “inverse”.

Accepted Answer

Introduction / Context: Object Definition Language (ODL) lets designers specify classes, attributes, and relationships in object-oriented databases. The keyword “inverse” appears when defining how two relationship ends correspond, ensuring navigation and referential consistency in both directions. Given Data / Assumptions: The question concerns ODL syntax and semantics. “inverse” is used to link two ends of the same association. Classes and attributes exist, but “inverse” specifically ties association roles. Concept / Approach: In ODL, a relationship declares an association between classes. The inverse clause identifies the opposite role at the other class so updates on one side are reflected on the other, avoiding divergence (e.g., relationship Set courses inverse Course::students;). Step-by-Step Solution: Identify where “inverse” appears: within relationship declarations.Recognize its purpose: tie two navigational ends (roles) of a single association.Conclude the construct: it pertains to relationships, not classes or attributes. Verification / Alternative check: Review standard ODL examples; “inverse” always pairs relationship roles across two classes to maintain bidirectionality. Why Other Options Are Wrong: Class: “inverse” does not declare classes. Attribute: intrinsic properties have no inverse ends. All of the above: overbroad; only relationship roles use “inverse”. Common Pitfalls: Assuming inverse is optional when cardinality rules require synchronization; omitting it can cause orphaned links in navigation. Final Answer: Relationship

Question 2

In ODL/ODMG-style schemas, the reserved word “enum” is used for what purpose? Choose the most accurate description of where enumerations are applied.

Accepted Answer

Introduction / Context: Enumerated types (enum) restrict a value to one of a fixed set of symbolic constants. In object-oriented data models and ODL-like DDLs, enums are commonly used to constrain attribute domains (e.g., status ∈ {Pending, Approved, Rejected}). Given Data / Assumptions: Enum declares a finite set of literal values. Attributes can be typed using enums. Classes and relationships are structural, not enumerated literal sets. Concept / Approach: An enum defines an attribute domain. After declaring the enum, attributes may use that type so stored values are validated against the allowed literals. Classes and relationships are not “ranged” by enums; they define structure and links, not constrained atomic values. Step-by-Step Solution: Define enumeration: a set of named constants.Bind enumeration to attributes that need constrained values.Conclude: enums serve attribute ranges, not class/relationship definitions. Verification / Alternative check: Schema examples show enum declarations used as attribute types (e.g., attribute Status status;), never as class or relationship ranges. Why Other Options Are Wrong: Class: structural definition; not a finite literal domain. Relationship: links objects; not an atomic literal type. All of the above: too broad; only attribute domains fit. Common Pitfalls: Encoding enums as free-text strings without validation; mixing display labels with stored enum identifiers. Final Answer: To define a range for an attribute.

Question 3

In collection semantics used with object databases and OQL, which structure is an unordered collection that may contain duplicate elements? Pick the most accurate term.

Accepted Answer

Introduction / Context: Understanding collection semantics is essential when modeling associations and query results. Different collection types offer different guarantees about order and uniqueness, which affect both correctness and performance in queries and methods. Given Data / Assumptions: Unordered vs. ordered distinctions matter. Allowance of duplicates is the deciding characteristic here. Standard types: set, bag (multiset), list, dictionary (map). Concept / Approach: A bag (multiset) is unordered and allows duplicates. A set is unordered and forbids duplicates. A list preserves order and allows duplicates. A dictionary (map) stores key–value pairs with unique keys rather than allowing duplicate elements freely. Step-by-Step Solution: Check “unordered” → narrows to set or bag.Check “may contain duplicates” → eliminates set; bag qualifies.Answer: Bag. Verification / Alternative check: OQL/ODMG documentation and many programming languages’ collection libraries (e.g., multiset) match the same definitions. Why Other Options Are Wrong: Set: no duplicates allowed. List: ordered sequence. Dictionary: keyed collection; duplicates governed by keys, not elements. Common Pitfalls: Assuming list-without-sorting is “unordered”; lists still maintain insertion/positional order. Confusing bag with set. Final Answer: Bag

Question 4

In ODL schema design, how should an association between two classes be specified to ensure consistent bidirectional navigation and integrity? Select the best practice regarding relationship declaration.

Accepted Answer

Introduction / Context: ODL supports relationships between classes and allows explicit declaration of inverse roles. Declaring both ends ensures that updates on one side are reflected on the other, enabling reliable navigation and consistency. Given Data / Assumptions: Two classes are associated (e.g., Student–Course). We want consistent, bidirectional traversal. ODL offers an “inverse” clause to link roles. Concept / Approach: The recommended pattern is to declare the relationship on both classes with inverse clauses, e.g., relationship Set courses inverse Course::students; and relationship Set students inverse Student::courses;. This enforces a single logical association with two synchronized ends. Step-by-Step Solution: Define relationship on Class A with an inverse pointing to Class B’s role.Define the reciprocal relationship on Class B referencing Class A’s role.Rely on the ODBMS to maintain integrity across both ends. Verification / Alternative check: Inspect ODL examples; proper bidirectional modeling consistently uses “both directions” with inverse mapping. Why Other Options Are Wrong: One direction only: risks inconsistent navigation and stale links. Neither: provides no navigable association. Common Pitfalls: Defining two unrelated one-way relationships without inverse; leads to duplication and drift. Final Answer: Both directions.

Question 5

Which collection type represents an ordered collection of elements (all of the same type) in object data models and OQL? Choose the most appropriate term.

Accepted Answer

Introduction / Context: Different collection types capture different semantics about order and duplication, which affects query results and method contracts. Knowing these distinctions prevents subtle bugs in persistence and retrieval logic. Given Data / Assumptions: All elements share the same type (typical for declared collections). Order matters (positions/indexes are meaningful). Standard collection taxonomy applies: set, bag, list, dictionary. Concept / Approach: A list is an ordered sequence and typically allows duplicates. A set is unordered and forbids duplicates. A bag is unordered and allows duplicates. A dictionary is keyed by unique keys rather than positional index. Step-by-Step Solution: Check the “ordered” requirement → list.Confirm homogeneity (same type) → consistent with list declarations.Answer: List. Verification / Alternative check: ODMG and many ORMs align “List” with ordered collections; indexes are stable and queries can use positional operations. Why Other Options Are Wrong: Set/Bag: explicitly unordered. Dictionary: key–value store, not a plain ordered sequence. Common Pitfalls: Assuming set preserves insertion order; if order is required, do not model as set/bag. Final Answer: List

Question 6

With Object Query Language (OQL), which actions are supported when constructing queries over collections? Select the most comprehensive answer.

Accepted Answer

Introduction / Context: OQL provides SQL-like expressiveness for querying persistent object collections. Similar to SQL, it supports selection, projection, filtering, and duplicate control (e.g., DISTINCT), making it suitable for rich object navigation and aggregation. Given Data / Assumptions: Collections can be returned as-is or filtered. Duplicate elimination may be requested (e.g., DISTINCT semantics). Predicates (criteria) determine subsets. Concept / Approach: OQL queries can return full collections (bags/lists) possibly with duplicates; they can also request duplicate-free results analogous to SQL DISTINCT. Predicates in WHERE clauses (select-from-where) enable returning subsets that match specified conditions. Step-by-Step Solution: Return entire collection → simple projection from the extent or relationship.Remove duplicates → apply DISTINCT-like semantics.Restrict subset → apply WHERE with criteria. Verification / Alternative check: Canonical OQL syntax mirrors SQL capabilities, supporting all three behaviors depending on the query. Why Other Options Are Wrong: Each single option is valid but incomplete; only “All of the above” covers the full capability set. Common Pitfalls: Forgetting to use DISTINCT when semantics demand uniqueness; returning overly large collections without filtering. Final Answer: All of the above.

Question 7

Object Query Language (OQL) is most similar to which query style and clause structure? Choose the most accurate characterization.

Accepted Answer

Introduction / Context: OQL was designed to be familiar to practitioners of SQL while supporting object features such as path expressions and navigations through relationships. Its overall clause ordering and semantics strongly resemble SQL. Given Data / Assumptions: The query language is intended to be SQL-like. Standard clause ordering is SELECT … FROM … WHERE … Object navigation augments, not replaces, SQL-style structure. Concept / Approach: OQL adopts the well-known select–from–where structure. The FROM clause introduces extents or collections; WHERE filters; SELECT projects results. Additional constructs (e.g., GROUP BY) may also appear, but the basic skeleton mirrors SQL. Step-by-Step Solution: Identify the canonical ordering used by SQL.Map OQL clauses to the same pattern.Confirm similarity rather than difference. Verification / Alternative check: Textbook OQL examples consistently show SELECT–FROM–WHERE, often with path expressions in the select list or predicates. Why Other Options Are Wrong: Select-where (without FROM) and from-where omit essential structure. “Not similar to SQL” contradicts the design goal of OQL. Common Pitfalls: Assuming OQL abandons relational thinking entirely; in practice it blends SQL familiarity with object navigation. Final Answer: Similar to SQL and uses a select-from-where structure

Question 8

In object data models, which of the following qualifies as an atomic literal type? Select the most comprehensive correct choice.

Accepted Answer

Introduction / Context: Atomic literals are indivisible values used as attribute domains and query constants. Typical atomic types mirror programming language primitives and common scalar types supported by the database engine. Given Data / Assumptions: We are considering scalar, non-collection types. Examples span text, numeric, and logical domains. Object identifiers and collections are excluded. Concept / Approach: Strings (text), Boolean (true/false), and Long (integral numeric) are all canonical atomic literal types. They serve as attribute types and constants in queries and constraints, independent of object identity and relationships. Step-by-Step Solution: Check indivisibility: each is a scalar value.Confirm common use as attribute domains.Aggregate to the most comprehensive valid choice. Verification / Alternative check: ODMG/ODL examples include attributes of types string, boolean, and integral numeric variants. Why Other Options Are Wrong: Each single choice is correct but incomplete; only “All of the above” captures the full set presented. Common Pitfalls: Confusing object identifiers (OIDs) with atomic values; treating collections as atomics. Final Answer: All of the above.

Question 9

The Object Definition Language (ODL) in object-oriented database systems is best described as what? Select the most complete characterization.

Accepted Answer

Introduction / Context: ODL provides a formal way to declare classes, attributes, relationships, keys, and other schema-level constructs for object-oriented databases. It plays the same role for OODBs that SQL DDL plays for relational systems. Given Data / Assumptions: We are discussing schema design, not ad-hoc queries. ODL captures logical structure of persistent objects. Implementations use ODL to realize logical schemas in the database. Concept / Approach: ODL is simultaneously a data definition language and a means to develop and implement logical schemas. It defines types and relationships that the ODBMS enforces, enabling storage, navigation, and integrity consistent with object modeling. Step-by-Step Solution: Recognize ODL as DDL for OODBs.Acknowledge its role in logical schema design.Accept that actual schema implementation proceeds from the ODL declarations. Verification / Alternative check: Documentation positions ODL as the schema language; tools often generate storage structures from ODL definitions. Why Other Options Are Wrong: Each single statement is true but incomplete; “All of the above” is the most complete description. Common Pitfalls: Assuming ODL also specifies behavior/method bodies; ODL focuses on structure and constraints. Final Answer: All of the above.

Question 10

Consider the declaration: ABC123 course(); Identify the class (type) name referenced in this statement and not the variable or function name.

Accepted Answer

Introduction / Context: Understanding basic declaration syntax helps avoid confusion between types (classes) and identifiers (variables/functions). In many C++/Java-like notations used in textbooks, a statement may either declare a variable of a class or, depending on the context, a function returning that class. Given Data / Assumptions: The token order is “ABC123 course();”. “ABC123” precedes the identifier “course”. Parentheses suggest a function-like syntax in C++ (a function returning ABC123) or a constructor-style call in pseudocode; in either case, the class/type token remains “ABC123”. Concept / Approach: In declarations, the first token typically denotes the type. Thus, “ABC123” is the class (type) name, while “course” is an identifier (variable or function name depending on language rules). The parentheses “()” are part of a function signature, not the class name. Step-by-Step Solution: Identify the leftmost token → “ABC123”.Map leftmost token to type/class in common declaration syntax.Confirm that “course” (or “course()”) is the identifier/signature, not the type. Verification / Alternative check: Compare to examples like Student enroll(); or Student s;—in both, “Student” is the class/type name. Why Other Options Are Wrong: “course” is an identifier, not a type. “course()” is a function signature, not a class name. “All of the above” cannot be correct because only one token is the class/type. Common Pitfalls: Confusing constructor-style calls with type names; treating parentheses as part of a name. Final Answer: ABC123

Question 11

Java Inheritance — Understanding 'class Manager extends Employee' In object-oriented programming with Java syntax, what is the correct interpretation of the declaration: class Manager extends Employee?

Accepted Answer

Introduction: Understanding the Java keyword extends is fundamental to object-oriented design. The declaration class Manager extends Employee expresses single inheritance, where one class derives behavior and state from another. This question tests whether you can correctly identify the role of Manager (child) relative to Employee (parent) and whether the code shown implies that Manager is abstract or concrete. Given Data / Assumptions: The declaration provided is exactly: class Manager extends Employee No abstract keyword is shown before class. In Java, extends denotes that the left-hand class inherits from the right-hand class. Abstract classes in Java must be declared with the abstract keyword. Concept / Approach: In Java, when class B extends A, B is the subclass (child, derived class) and A is the superclass (parent, base class). The absence of the abstract keyword means the class is concrete by default, capable of being instantiated (assuming it has an accessible constructor and no abstract methods inherited without implementation). Therefore, Manager is the subclass and Employee is the superclass. Nothing in the snippet implies that Manager is abstract. Step-by-Step Solution: 1) Read the syntax: class Manager extends Employee.2) Recognize extends indicates inheritance with Manager as the child and Employee as the parent.3) Check for abstract: not present, so Manager is concrete by default.4) Conclude: Manager is a concrete subclass of Employee. Verification / Alternative check: You can compile a minimal example where Employee is a simple class and Manager extends Employee; instantiating new Manager() works unless abstract constraints are introduced. If abstract methods exist in Employee and are not implemented in Manager, then Manager must itself be declared abstract. That is not indicated here. Why Other Options Are Wrong: Superclass options (a, c): Manager is not the superclass; Employee is. Abstract options (c, d): The snippet does not declare abstract; default is concrete. Interface option (e): Implements relates to interfaces; extends here denotes class inheritance. Common Pitfalls: Assuming that any class that extends another must be abstract, or confusing extends (classes) with implements (interfaces). Also, forgetting that Java supports single inheritance for classes and multiple inheritance via interfaces. Final Answer: Manager is a concrete class and a subclass.

Question 12

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

Accepted Answer

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

Question 13

Object Database Management Systems (ODBMS) — Capabilities vs. Myths Which statement accurately reflects the strengths and realistic adoption of ODBMS technology in comparison to relational databases?

Accepted Answer

Introduction: Object database management systems (ODBMS) were designed to persist complex application objects with identity, encapsulation, and navigational access. This question asks you to separate real capabilities from exaggerated claims and mismatches, especially in contrast to highly prevalent relational database systems (RDBMS). Given Data / Assumptions: ODBMSs support complex types, nested structures, and direct object references. RDBMSs dominate many enterprise workloads, especially tabular OLTP. The options include both accurate capabilities and overstatements. Concept / Approach: Focus on what ODBMSs genuinely do well: storing complex objects, graphs, and multimedia or document-like structures, often used by web applications and engineering systems. Claims that ODBMSs have overtaken RDBMSs across all applications are inaccurate, and saying they are most useful for traditional two-dimensional tables contradicts their purpose. Therefore, identifying a valid capability without overstating market dominance is the key. Step-by-Step Solution: 1) Evaluate option (a): storing complex data types for web contexts is aligned with ODBMS strengths.2) Evaluate option (b): overtaking RDBMSs for all applications is incorrect; RDBMSs remain prevalent.3) Evaluate option (c): two-dimensional tables suit RDBMSs; this is not an ODBMS advantage.4) Option (d) cannot be true because (b) and (c) are false.5) Select (a) as the accurate, measured statement. Verification / Alternative check: Industry adoption trends show RDBMSs leading transactional workloads, while ODBMSs have niches in CAD/CAM, simulations, and certain content or web applications where object persistence is beneficial. Why Other Options Are Wrong: Overtaking RDBMSs (b): Unsupported by broad market evidence. Most useful for 2D tables (c): Contradicts ODBMS design goals. All of the above (d): Fails due to the false statements included. Extra summary (e): While generally true as a commentary, it is not among the original correct choices intended by the question's style. Common Pitfalls: Assuming one data model suits every workload or conflating capability with market dominance. Choose the statement that is true without exaggeration. Final Answer: They have the ability to store complex data types on the Web.

Question 14

ODL (Object Definition Language) — Association Degree Support Within ODL, which degrees of association relationships are supported when modeling links between objects?

Accepted Answer

Introduction: ODL (Object Definition Language), as used in ODMG-style object databases, describes classes, attributes, relationships, and constraints for persistent objects. A frequent modeling question is how many participating object types an association can connect (its arity or degree). Given Data / Assumptions: ODL models relationships explicitly, often with role names and cardinalities. Associations may be unary (reflexive), binary, ternary, or higher. The question asks about the spectrum of support. Concept / Approach: Just like conceptual ER modeling, object models can define relationships of arbitrary degree. Although higher-arity relationships are less common and may sometimes be decomposed into sets of binary links with additional classes, the language and modeling approach conceptually allow arbitrary arity when it accurately represents the domain semantics. Step-by-Step Solution: 1) Recognize that unary associations relate an object to itself (for example, manages relationship).2) Binary associations connect two object types (for example, Customer–Order).3) Ternary associations connect three object types (for example, Supplier–Part–Project).4) Higher-degree associations are also representable, though sometimes normalized via helper classes.5) Therefore, ODL supports unary, binary, ternary, and higher-degree associations. Verification / Alternative check: Modeling literature and ODL examples include n-ary associations; practical systems may recommend decomposition for clarity or performance, but the language and modeling concept do not forbid higher arity. Why Other Options Are Wrong: Unary only / Binary only: Too restrictive; does not reflect ODL's modeling scope. Up to ternary only: Artificial cut-off; higher-arity is possible. Common Pitfalls: Forcing all real-world ternary or higher constraints into binary links and then losing the intended semantics. When decomposition is used, ensure constraints are preserved with additional classes and checks. Final Answer: Unary and Binary and Ternary and higher

Question 15

ODL (Object Definition Language) — Elements You Can Define When authoring an object schema with ODL, which categories of elements can be defined directly?

Accepted Answer

Introduction: ODL is a schema definition language for object databases that describes persistent types and their behavior. Understanding the breadth of elements you can define in ODL helps you design expressive object schemas that capture state (attributes and structures) and behavior (operations) where appropriate. Given Data / Assumptions: ODL is associated with ODMG object databases. Object schemas typically comprise classes, attributes, relationships, and operations. The language supports composite type definitions (structures) and behavior declarations. Concept / Approach: Attributes capture scalar or complex values on objects. Structures allow composition of multiple fields into a single typed value. Operations define callable behaviors associated with classes or interfaces. Together, they form the core of an object schema's state and behavior specification in ODL. Step-by-Step Solution: 1) Confirm that attributes are first-class schema elements in ODL.2) Recognize that structured types (records) can be declared for reuse and clarity.3) Note that operations (methods) can be declared in interfaces/classes to define behavior signatures.4) Therefore, all listed elements are definable in ODL. Verification / Alternative check: Review ODL examples that declare interfaces with attributes, relationships, struct types, and operation signatures; these constructs are standard in ODMG-style schemas. Why Other Options Are Wrong: Only one category: Too narrow; ODL supports multiple element kinds. Only classes: Misstates ODL's scope; attributes and operations are integral. Common Pitfalls: Designing overly complex structures without considering normalization and navigability, or declaring operations in the schema that belong better in application-layer services. Final Answer: All of the above.

Question 16

In ODMG's Object Definition Language (ODL), if all possible values of an attribute are known in advance, can those values be explicitly enumerated in the type declaration (for example, by using an enumeration to restrict the attribute domain)?

Accepted Answer

Introduction / Context: Object database standards such as the ODMG model define ODL (Object Definition Language) to declare classes (interfaces), attributes, relationships, keys, and extents. A frequent design task is to constrain an attribute to a small, closed list of allowed values. This question checks whether ODL supports that pattern by allowing enumeration of all valid values directly in the type system. Given Data / Assumptions: We are using ODMG-style ODL to model persistent classes and their attributes. The attribute in question has a finite, known set of values (for example, status ∈ {NEW, ACTIVE, SUSPENDED}). We want a schema-level constraint rather than only runtime checks. Concept / Approach: ODL supports literal types and type declarations, including enumerations. When the domain is closed and known, an enumeration provides a compact, precise way to express the allowed values. This improves clarity and minimizes invalid data by preventing values outside the list from being assigned. Step-by-Step Solution: Decide the attribute requires a closed set of values.Define an enumeration type in the ODL schema to list those values.Declare the attribute using that enumeration type.Persist and query objects; the type system ensures only enumerated values are stored.Document semantics for each enumerated constant to aid application developers. Verification / Alternative check: Compare the enumeration approach against using a free-form string. With enumeration, tools can catch invalid assignments during compilation or schema validation; without it, mistakes become runtime data-quality issues. Why Other Options Are Wrong: Restricting to numerics only (option c) is incorrect; enumerations cover many literal kinds. Keys-only (option d) misunderstands keys versus attribute domains. Transient-only (option e) is unrelated; enumerations apply equally to persistent classes. Saying ODL cannot restrict an attribute (option b) ignores enumeration support. Common Pitfalls: Overusing enumerations for values that actually change over time (better modeled as reference objects); failing to version enumerations when business states evolve; mixing display labels with internal enumeration constants without a mapping layer. Final Answer: Applies — ODL allows enumerating all permissible values for an attribute

Question 17

According to the ODMG Object Model, are relationships directly supported only as unary (recursive) or binary links between classes, with n-ary associations modeled via intermediate objects rather than native n-ary relationship syntax?

Accepted Answer

Introduction / Context: Relationship modeling is central to object databases. The ODMG Object Model and ODL provide a built-in way to declare relationships with optional inverse specifications, enabling bidirectional navigation and referential integrity. This item examines whether ODMG supports only unary (a class related to itself) and binary (between two classes) relationships directly, leaving n-ary associations to be represented via association objects. Given Data / Assumptions: ODMG ODL is used to declare attributes and relationships. Unary is a special case of binary where both ends are the same class (recursive relationship). No special native ODL syntax exists for relationships among three or more classes in one declaration. Concept / Approach: ODL declares relationship members between two classes, typically coupled with an inverse relationship to maintain consistency. When a conceptual model includes an n-ary relationship, standard practice is to introduce an association (link) class that holds the participants; the n-ary association becomes a regular object with binary relationships to each participant. Step-by-Step Solution: Identify an n-ary requirement (e.g., Student–Course–Semester).Create an association class (e.g., Enrollment) capturing attributes of the relationship.Declare binary relationships from the association class to each participant with inverses.Use instances of the association class to represent each n-ary link.Navigate via the association object to access all related participants. Verification / Alternative check: Review ODL grammar and examples: you will find binary relationship declarations, not direct n-ary constructs. Industry texts show association objects as the idiomatic solution. Why Other Options Are Wrong: Option b is incorrect because native n-ary relationship syntax is absent in ODL. Options c, d, and e introduce irrelevant constraints (persistence, key composition, or extents) that do not change the binary nature of ODL relationships. Common Pitfalls: Forgetting to declare inverses, causing asymmetric navigation; embedding relationship attributes on a participant class rather than on the association object; attempting to simulate n-ary links with multiple overlapping binaries without a central association, which loses integrity. Final Answer: Applies — ODMG directly supports only unary/binary relationships

Question 18

In ODMG ODL, must a class's extent (the set of its persistent instances) be specified before declaring a key for that class, since keys uniquely identify objects within an extent?

Accepted Answer

Introduction / Context: In ODMG, an extent is the named collection containing all persistent objects of a class. A key identifies objects uniquely within that extent. Understanding the dependency between these declarations is essential for correct schema design and for consistent object identity semantics across the database. Given Data / Assumptions: Each persistent class may declare one or more extents. Keys are defined to enforce uniqueness of attribute values within a specific extent. ODL declarations for a class typically include both extent and key in the class header. Concept / Approach: Because keys are applied to a collection of objects, the extent needs to exist conceptually before the key can be meaningfully interpreted. The common ODL idiom lists the extent first and the key second in the class/interface header, signaling that the key constrains members of the already-declared extent. Step-by-Step Solution: Declare the class/interface.Name the extent that will hold persistent instances.Declare the key that uniquely identifies instances inside that extent.Define attributes and relationships that participate in the key as needed.Implement operations; the key semantics carry through persistence and querying. Verification / Alternative check: Examine canonical ODL examples: class headers typically show extent followed by key. This ordering expresses the logical dependency of a key on its target collection. Why Other Options Are Wrong: Option b ignores the link between uniqueness and the collection to which uniqueness applies. Options c–e add conditions (composite, transient, relationship-based) that do not alter the fundamental dependence. Common Pitfalls: Choosing a non-stable attribute for the key; forgetting that keys must be unique across the full extent, not just within subgroups; misunderstanding that keys are about value-based identity, distinct from underlying object identifiers managed by the system. Final Answer: Applies — the extent is declared before the key for that class

Question 19

In ODMG ODL syntax, are operations (methods) specified by writing the operation name followed by parentheses and parameters, analogous to method signatures in object-oriented languages?

Accepted Answer

Introduction / Context: ODL borrows familiar object-oriented declaration patterns for interfaces and operations. Developers who know C++ or Java method signatures will recognize the form used to declare operations in ODL. This question confirms whether operations are declared using the conventional “name + parenthesis” syntax. Given Data / Assumptions: Interfaces (classes) in ODL can declare operations alongside attributes and relationships. Operations have names and parameter lists; they may specify return types and exceptions. We are concerned with the syntactic convention for denoting operations. Concept / Approach: ODL defines operations with a method-like signature: return_type opName(param_list). Parentheses delimit the optional parameter list, mirroring mainstream object-oriented languages and easing adoption by developers. Step-by-Step Solution: Define the interface (class) in ODL.Declare the operation name immediately followed by parentheses.Provide zero or more parameters inside the parentheses, with types.Optionally declare exceptions or modifiers permitted by ODL.Reference the operation from applications or bindings to invoke behavior. Verification / Alternative check: Consult ODL grammar in standard references: the production rules show an operation declared with parentheses after the identifier, not square brackets or other delimiters. Why Other Options Are Wrong: Brackets (option b) are not used to declare operations. Abstract-only (option c) is false; the syntax applies to both concrete and abstract operations. Relationship blocks (option d) define links, not operations. Parameterless-only (option e) is incorrect; parameters are permitted and common. Common Pitfalls: Confusing attribute accessors with explicit operations; forgetting that operation semantics are outside ODL's persistence semantics, which focus on structure and identity rather than behavior implementation. Final Answer: Applies — operations use parentheses after the name

Question 20

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?

Accepted Answer

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

Object-Oriented Database Questions