Computer Science Previous Year Questions (page 8)

Explanation

COBWEB is an incremental system for hierarchical conceptual clustering. COBWEB incrementally organizes observations into a classification tree. Each node in the classification tree represents a class (concept) and is labeled by a probabilistic concept that summarizes the attribute-value distribution of objects classified under the node.

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Data warehouse is a subject oriented integrated, time variant and non volatile collection of data in support of management decision making process. A data warehouse is a copy of transaction data specifically structured for query & analysis.

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A decision tree can be used to visually and explicitly represent decision & division making. In data mining, a decision tree describes data but not decisions; rather the resulting classification tree can be an input for decision making.

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Association rule learning is a method for discovering intersecting relations between variables in large data base. It is intended to identify strong rules disconnected in database using some measures of interestingness.

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SELECT A, COUNT(*) FROM R; is illegal: when an aggregate function (SUM, AVG, COUNT, MAX, MIN) is used in the SELECT clause along with a non-aggregated attribute, a GROUP BY clause on that attribute is required. SELECT A, B, COUNT(*) FROM R GROUP BY A, B; is legal.

Explanation

Accessing the data from the database in DBMS done through DML (Data manipulation language). The DML command can access the data from a database.

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Relational database schema normalization is not for reducing the number of joins required to satisfy a query (normalization usually increases joins). Its goals are eliminating redundancy and anomalies and enforcing functional dependencies.

Explanation

(1) NULL values can be used to opt a tuple out of enforcement of a foreign key: correct. (2) If a table has only one candidate key and is in 3NF, then it is also in BCNF: correct. (3) Projection (Π) in relational algebra eliminates duplicate tuples while SQL SELECT returns all of them: correct. So (1), (2) and (3) are true.

Explanation

Fast Ethernet:- Cabling, 100 Base- Tx uses twisted pair cable and maximum segment size is 100 metres.

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Throughput = (12,000 × 10,000) / 60 bits per second = 2,000,000 bps = 2 Mbps. So answer is option (b).

Explanation

The correct match: Session layer – manage dialogue control (A-iv); Application layer – virtual terminal software (B-i); Presentation layer – semantics of the information transmitted (C-ii); Transport layer – flow control (D-iii).

Explanation

IMAP : The basic idea behind IMAP is for all email server to maintain a central repository that can be accessed from any machine

Explanation

The main drawback of the waterfall model is the difficulty of accommodating change after the process is under way. (1) Difficult to address change: Inflexible partitioning of the project into distinct stage makes it difficult to respond to changing customer requirements. Therefore, this model is only appropriate when the requirement are well understood and changes will be fairly limited during the design process

Explanation

Prototype typically simulates only a few aspects of, and may be completely different from, the final product. Prototyping has several benefits. The software designer and implementer can get valuable feedback from the user early in the project.

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Specificity (lack of ambiguity) of requirements is measured as Q = n₁/n₂, the fraction of requirements in the specification for which all reviewers have identical interpretations. So the answer is option (a).

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For a program of k variables, boundary value analysis yields 4k + 1 test cases. Robustness testing yields 6k + 1 and worst-case testing yields 5ᵏ test cases.

Explanation

Reliability is the probability of failure free operation of a system over a specified time within a specified environment for a specified purpose.

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A friend function of a class is defined outside that class's scope but has the right to access all private and protected members of the class. Even though the prototypes for friend functions appear in the class definition, friends are not member functions.

Explanation

C++ provides two kinds of templates: class templates and function templates. A function template in C++ provides two levels of generalization.

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XOR is linearly inseparable. NOTXOR is just XOR with the 1's swapped with 0's and vice versa; swapping the labels on the points does not alter the structure of the space, so NOTXOR is also linearly inseparable. AND, OR and NOR are linearly separable.

Explanation

These are fundamental duality theorems of linear programming. All three statements are correct.

Explanation

A ripple counter is an asynchronous counter where only the first flip-flop is clocked by an external clock. All subsequent flip-flops are clocked by the output of the preceding flip-flop. Asynchronous counters are also called ripple counters because of the way the clock pulse ripples its way through the flip-flops.

Explanation

Max-product composition: T(x, z) = max over y of R(x, y) × S(y, z). T(x₁, z₁) = max(0.7 × 0.9, 0.5 × 0.1) = 0.63; T(x₁, z₂) = max(0.42, 0.35) = 0.42; T(x₁, z₃) = max(0.14, 0.25) = 0.35. T(x₂, z₁) = max(0.72, 0.04) = 0.72; T(x₂, z₂) = max(0.48, 0.28) = 0.48; T(x₂, z₃) = max(0.16, 0.20) = 0.20. So T = x₁: [0.63 0.42 0.35], x₂: [0.72 0.48 0.20].

Explanation

(r + s)* generates any string over r and s, the same as (s + r)*. (r*)* generates any string of r's, the same as r*. (r* s*)* also generates any string over r and s, the same as (r + s)*. All the identities are true.

Explanation

Interrupt Mask Register (IMR): An Interrupt mask register is a specialized register in a computer's CPU or a dedicated peripheral used to enable or disable (mask) individual interrupt lines.

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In register indirect addressing, the location (address) of the operand in memory is held in a register that is specified in the instruction.

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ALU is designed to operate on 8-bit data therefore the 8085 microprocessor has 8-bit ALU.

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DAD H: double add HL to HL⇒HL=HL+HL

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Radix sort performs one stable counting sort per digit; each pass takes O(n + k) time and there are d digits. So n integers of d digits, each digit in {1, 2, ..., k}, are sorted in O(d(n + k)) time.

Explanation

z is maximized by taking x₁ = 0 and x₂ as large as possible: 5x₂ ≤ 80 gives x₂ = 16 (and x₁ + x₂ = 16 ≤ 20). So when x₁ = 0 and x₂ = 16, Max z = 0.50 × 16 = 8.

Explanation

Inside funb( ), x refers to y of main, and both y and z refer to x of main. y = y + 4 makes main's x = 14. z = x + y + z = 3 + 14 + 14 = 31, which is stored in main's x. main's y is unchanged (3). Printed output is 31, 3.

Explanation

A constructor resembles an instance method, but it differs from a method since it has no explicit return type, it is not implicitly inherited and it usually has different rules for scope modifiers.

Explanation

To disallow a method from being overridden, specify final as a modifier at the start of its declaration. Methods declared as final cannot be overridden.

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Composition is a strong type of association between two classes with full ownership. Child objects do not have their own lifecycle without the parent object; if a parent object is deleted, all its child objects are also deleted.

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An abstract class cannot be directly instantiated with the new operator; since an abstract class does not contain a complete implementation, it is not possible to create an abstract object.

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Java uses threads to enable the entire environment to be asynchronous. This helps reduce inefficiency by preventing the waste of CPU cycles.

Explanation

Converting 30 days into minutes, the fraction of time the system is not available = 10/(30 × 24 × 60) × 100 ≈ 0.023%. Availability = 100 – 0.023 ≈ 99.97%.

Explanation

The file control block and the index block are already in memory, so for indexed allocation only the new block has to be written to disk: 1 disk I/O operation. (Contiguous and linked allocation would need 1 and 3 operations respectively in this scenario, per the book.)

Explanation

Effective access time = 0.99 × (1 µsec + 0.008 × 2 µsec) + 0.002 × (10000 µsec + 1000 µsec) + 0.001 × (10000 µsec + 1000 µsec) ≈ (0.99 + 0.016 + 22.0 + 11.0) µsec ≈ 34.0 µsec.

Explanation

With 5 frames: (1) LRU algorithm: total number of page faults = 8. (2) FIFO algorithm: total number of page faults = 10. (3) Optimal algorithm: total number of page faults = 7.

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ls -l lists the files with details, grep "June" keeps the lines for files modified in June, and sort +10n skips ten fields and sorts the lines in numeric order. So the correct command is ls -l | grep "June" | sort +10n.

Explanation

A process's nice value (priority) can be set at the time of creation with the nice command, which takes a command line as an argument, and adjusted later with the renice command. So I, II and III are all true.

Explanation

Completeness Condition: All the data of the global relation must be mapped into the fragments; it must not happen that a data item which belongs to a global relation does not belong to any fragment.

Explanation

EXCEPT returns the records present in the first relation and absent in the second, eliminating duplicates: SQ1 gives the single tuple <2, 5>. EXCEPT ALL keeps duplicates, removing one occurrence per matching tuple: SQ2 gives <2, 5> and <1, 6> (2 tuples). So the cardinalities are 1 and 2.

Explanation

Aliasing describes a situation in which a data location in memory can be accessed through different symbolic names in the program. Modifying the data through one name implicitly modifies the value associated with all aliased names.

Explanation

I. An OODBMS avoids the "impedance mismatch" problem: true. II. An OODBMS does not avoid the "phantom" problem. III. An OODBMS does not provide higher-performance concurrency control than most relational databases. IV. An OODBMS provides faster access to individual data objects once they have been read from disk: true. So I and IV only.

Explanation

Each route (hop) takes 8000/32000 = 0.25 second. For all 8 routes the total delay = 8 × 8000/32000 = 2 seconds.

Explanation

Statement I– True, High speed Ethernet can utilize various media, including optical fiber. It's not limited to just copper cables. Statement II– True, the definition of PPPoE is to encapsulate PPP frames within Ethernet frames. Statement III– False Since high speed Ethernet can work on optic fiber, this statement in incorrect. Statement IV– False, The correct encapsulation is PPP frames inside Ethernet frames.

Explanation

Code-and-fix: write some code, debug it, repeat (A-5). Evolutionary prototyping: the system is developed incrementally by evolving the specification and code (B-2). Spiral model: assess risks at each step (C-1). Staged delivery: requirements for several releases first, then design and code in sequence (D-3). Waterfall model: sequential, non-iterative standard phases (E-4).