Which are the two ways in which entities can participate in a relationship?
Answer: B
Correct answer: Total and partial
Participation is total when every entity of the set must take part in the relationship - every loan must have a borrower - and partial when only some need to. In an E-R diagram total participation is drawn with a double line.
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Microsoft Access is an enterprise-class database product.
Answer: B
Correct answer: False
Access is a personal or workgroup product: it bundles a small DBMS with an application generator in a single file, which suits one user or a handful. Enterprise-class products - SQL Server, DB2, Oracle - run as separate servers and are built for many concurrent users, large volumes and serious administration.
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Conceptual design
Answer: C
Correct answer: Involves modelling independent of the DBMS
Conceptual design captures what the organisation needs to record - entities, attributes and relationships - without reference to any particular product. Choosing tables and types is logical design, and sizing and tuning belong to physical design; keeping them separate is what lets the same conceptual model be implemented on any DBMS.
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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One of the reasons why OODBMSs have not been widely used for business information systems is that OOP is obsolete.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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