Introduction To Database Questions and Answers

Answer: B

SQL Server is the database management system developed by Microsoft. Oracle Database is made by Oracle Corporation, MySQL began as an open-source system of a separate company and is now owned by Oracle, and PostgreSQL is developed by an open-source community, so none of those three is a Microsoft product. Its first release was in the late 1980s as a database server, and it is today a common choice for business applications on Windows.

Answer: C

The correct match is I - N, II - M, III - L.

The three levels of the ANSI-SPARC architecture:

• the logical (conceptual) schema describes the data as relations, their attributes and constraints (N);
• the physical schema describes how those relations are stored: file organisation and indexes (M);
• the external schema is what each user or application sees, defined as views over the relations (L).

The options that link the logical schema to views or to file organisation, or the physical schema to views, mix up these levels.

Answer: A

A DBMS is transparent if it keeps hidden a physical structure from user.

Transparency in a DBMS means the user works with data without knowing how it is stored: file organisation, indexes, storage devices, and in a distributed database where fragments and copies are kept. This is the physical data independence of the three-schema architecture.

The logical structure, the tables, attributes and relationships, is exactly what users and programs work with, so it is not hidden. Hiding sensitive information is a matter of security and authorisation through views and privileges, not of transparency.

Answer: A

Part of the data will be cut-off.

A field defined with a fixed size, for example a text field of 20 characters, can store only that many characters. If longer data is entered, the extra characters are truncated, or in a strict system the entry is rejected; either way the field does not hold the full value.

The program does not freeze, and a fixed-size field does not adjust itself or become flexible. That is why field sizes must be chosen with the longest expected value in mind.

Answer: C

The object-based logical model is the Entity Relationship Model.

Korth and Silberschatz divide data models into object-based logical models, record-based logical models and physical models. Object-based models describe data in terms of objects (entities) and their relationships; the entity-relationship model and the object-oriented model are the standard examples.

The network, hierarchical and relational models are record-based logical models: the database is structured as fixed-format records of several types, linked by pointers in the first two and by values in tables in the relational model.

Answer: C

The one that is not a Codd rule is The structure definition stored in data dictionary should be accessible to all users.

Codd's rule 4 (dynamic online catalogue) requires the database's description to be stored like ordinary data and to be queryable by authorised users with the same relational language, not by all users.

The other options paraphrase real rules: the information rule (all data in tables), rule 3 (systematic treatment of nulls) and rule 7 (high-level insert, update and delete of sets of rows as well as single rows).

Answer: A

The true statements are (i) and (iii).

In the three-schema architecture, logical data independence is the capacity to change the conceptual schema without having to change the external schemas or application programs (i). Physical data independence is the capacity to change the internal schema without having to change the conceptual schema (iii).

Statement (ii) mixes the two levels: changing the conceptual schema does not normally touch the internal schema. Statement (iv) gives physical independence the definition of logical independence.

Answer: C

A database is an organized collection of data or information that can be accessed, updated and managed.

A database stores structured data so that it can be easily retrieved, modified and administered, usually through a database management system that also provides security, integrity and concurrent access.

The other options each restrict the definition to only access or only management, or forbid updating, all of which contradict what a database is for.

Answer: A

The relational DBMS is MySQL.

MySQL stores data in tables of rows and columns, uses SQL and enforces keys and relationships, which makes it a relational database management system.

MongoDB is a NoSQL document database, Cassandra a NoSQL wide-column store, and Hadoop a framework for distributed storage and processing of big data, not an RDBMS.

Other relational DBMSs include Oracle Database, PostgreSQL and Microsoft SQL Server.

Answer: A

The structure of data is described by the Schema.

A database schema defines the tables, their columns and data types, keys and the relationships between tables: the logical design of the database, as distinct from the data in it at any moment.

A tuple is a single row of data, an index is a structure that speeds up searches, and a query is a request for data.