DBMS: the costs, and the tools you get

The problem

You would not hire a bus to carry one notebook across the road. A DBMS is powerful, but for a tiny job it can be “requiring too much to do too little”, as the book puts it.

So a DBMS has real costs. It also brings tools that plain files never had: a dictionary, a query language, a report generator and more.

Disadvantages: extra system overhead, extra staff training, costly mistakes from the wrong type of database, data as a shared corporate resource, and the need for a data dictionary. Features: data dictionary, utilities, query language (SQL), report generator, access security, and backup and recovery.

Key terms

System overhead

Extra time and resources a DBMS needs even for simple jobs, like reading a tape file, that plain processing would do quickly.

Data dictionary

A document or file that stores the data definitions: file names, field names, field sizes and data types. It can check entered data against these rules and control access.

SQL

An English-like command language for creating tables, entering data, and retrieving or updating records that meet given criteria.

Report generator

A program that produces an on-screen or printed document from the database, with row headings, column headings and page headers set in advance. Even non-experts can use it.

Short questions with model answers

1. Q1. Name the disadvantage. (a) Untrained staff write slow database calls. (b) A hierarchical database must be restructured at great cost. (c) Many organizations share the same data.

   • (a) additional training of staff
   • (b) wrong type of database environment
   • (c) data as a corporate resource

   training · wrong environment · corporate resource

2. Q2. Name the feature. (a) It stores field names, sizes and types. (b) The DBA gives a clerk read-only rights. (c) Lost data is reinstated after corruption.

   • (a) data dictionary
   • (b) access security
   • (c) backup and recovery

   dictionary · access security · backup/recovery

3. Q3. Write a query for: the records of Section B students with more than 400 marks. How many of the widget's six records match?

   • SELECT * FROM Students WHERE Section = 'B' AND Marks > 400
   • Ali 412 (B), Bilal 471 (B) → 2 records

   2 records (average 441.5)

Common mistakes

• ✗ Expanding SQL as “Standard” or “Sequential” Query Language.

  ✓ SQL stands for Structured Query Language, and it is a structured language.

• ✗ Saying the data dictionary stores the data.

  ✓ It stores the data definitions: file names, field names, field sizes and data types.

• ✗ Claiming a DBMS is always the better choice.

  ✓ For simple jobs it adds overhead, it needs trained staff, and the wrong type of database is costly to change.

MCQs

1. 1. SQL stands for:

   1. (a) Standard Query Language
   2. (b) Structured Query Language
   3. (c) Sequential Query Language
   4. (d) Simple Question Language
   Show answer

   (b) Structured Query Language.

2. 2. The data definitions are stored in the:

   1. (a) report generator
   2. (b) data dictionary
   3. (c) transaction file
   4. (d) query language
   Show answer

   (b) The data dictionary stores definitions such as field names, sizes and types.

3. 3. A program that produces a printed document from the database is a:

   1. (a) utility
   2. (b) report generator
   3. (c) data dictionary
   4. (d) query language
   Show answer

   (b) A report generator produces on-screen or printed documents with headings set in advance.

4. 4. Using a DBMS for a very simple job, like reading one tape file, mainly adds:

   1. (a) data integrity
   2. (b) system overhead
   3. (c) shareability
   4. (d) availability
   Show answer

   (b) It is “requiring too much to do too little”: extra time and resources.

5. 5. Which database systems are most sensitive to later changes in structure?

   1. (a) relational
   2. (b) network
   3. (c) hierarchical
   4. (d) all equally
   Show answer

   (c) The book says hierarchical systems are more sensitive than network or relational ones; relational changes are fairly easy.

Quick revision

• Disadvantages: system overhead, staff training, costly wrong environments, data as a corporate resource, and the need for a dictionary.
• Features: data dictionary, utilities, SQL, report generator, access security, and backup and recovery.
• SQL (Structured Query Language) retrieves and updates records by criteria using English-like commands.