The relational database model was created by E.F. Codd.
Answer: A
Correct answer: True
E. F. Codd, at IBM, set out the relational model in his 1970 paper “A Relational Model of Data for Large Shared Data Banks”. It replaced navigation through pointers with operations on sets of tuples, and every relational product since rests on it.
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One of the reasons why OODBMSs have not been widely used for business information systems is that OOP is obsolete.
Answer: B
Correct answer: False
Object-oriented programming is anything but obsolete - it is the mainstream. OODBMSs failed to displace relational systems for business use for quite different reasons: the enormous investment already in relational databases, the maturity of SQL and its tools, and the fact that most business data fits the relational model perfectly well.
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An instance of relational schema R (A, B, C) has distinct values of A including NULL values. Which one of the following is true?
Answer: B
Correct answer: A is not a candidate key
A candidate key must satisfy two conditions: uniqueness and no NULLs. Distinct values alone are not enough - a NULL means the value is unknown, so it cannot be relied on to identify a row, and two NULLs cannot even be compared for equality. Since A contains NULLs it is neither a candidate key nor a primary key.
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A logical schema
Answer: A
Correct answer: Is the entire database.
The logical (conceptual) schema is the complete description of the whole database - every table, column, key and constraint - as one community view. It is distinct from the internal schema, which says how the data sits on disk, and from the external schemas or subschemas, each of which shows one application its own slice.
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The purpose of a database is to help people stop using spreadsheets.
Answer: B
Correct answer: False
The purpose of a database is to keep track of things - particularly things with relationships among them, which a spreadsheet handles badly. Spreadsheets remain the right tool for calculation and analysis; the question is what kind of problem you have, not which tool to abolish.
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An application where only one user accesses the database at a given time is an example of a(n) ________ .
Answer: A
Correct answer: single-user database application
By definition: one user at a time means a single-user application - a personal address book or a small Access database. The distinction matters because concurrency control, locking and much of the administrative machinery exist only for the multi-user case.
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On which structure is the hierarchical model based?
Answer: A
Correct answer: Tree
The hierarchical model is based on the tree: one root, and every other record type with exactly one parent. Its successor, the network model, allows a record to have several parents and so is based on a graph.
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A database design may be based on existing data.
Answer: A
Correct answer: True
A design may well start from data that already exists - spreadsheets, legacy files, another system’s tables. The process is different from designing from requirements: the existing structures have to be analysed and normalised rather than derived, and this is where much real database work begins.
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In E-R diagram generalization is represented by
Answer: D
Correct answer: Triangle
Generalisation and its inverse, specialisation, are drawn as a triangle labelled ISA, connecting the general entity set above to the specialised ones below. An ellipse is an attribute, a dashed ellipse a derived one, and a rectangle an entity set.
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The following are functions of a DBMS except ________ .
Answer: A
Correct answer: creating and processing forms
A DBMS creates databases, processes data and provides the tools to administer them - backup, security, concurrency. Forms belong to the application, not to the DBMS: they are the user interface built on top of it. (Products such as Access blur the line by bundling both, which is what makes this question worth asking.)
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