CSC 675 Review 1 - Introduction and Overview

Question 1

Data

Answer 1

Known facts that can be recorded

Question 2

Database *

Answer 2

Collection of related data

Question 3

DBMS, Database Management System *

Answer 3

a collection of programs that enables users to create, access, and maintain a database

Question 4

Database Catalog / Meta-Data

Answer 4

structure of file

storage format of data items

constraints on the data

Question 5

program-data independence

Answer 5

allow the data file structure to be changed without modifying the application code

a layer in between

Question 6

What are the three major types of operations supported by database systems?

Answer 6

Create - define data

Access - query + update

Maintain - enforce integrity constrains

Question 7

Why are database applications considered to be easier to implement that traditional file based applications?

Answer 7

Because much of the functionality that you need is already defined.

Question 8

What is a database query?

Answer 8

Read and return all data which satisfy some search criteria.

Question 9

How do read-only queries differ from update queries?

Answer 9

update queries insert, delete or modify data values in the database, read-only queries don’t.

Question 10

Discuss how file based applications are different from database applications.

Answer 10

Databases are

• self describing
• insulation between programs and data
• data abstraction
• support multiple views of the data
• sharing data and multiuser transaction processing

In traditional file systems,
- files are part of each program.

Question 11

Why is it difficult for application programers to provide integrity constraint enforcement in their application code?

Answer 11

all in one place

collecting the integrity constraints into the database makes updating the integrity constraints themselves possible without rewriting application programs.

Question 12

What is concurrency control?

Answer 12

coordinate many simultaneous transactions

Question 13

Why is concurrency control important?

Answer 13

insure that simultaneous transactions work with a consistent database and leave the database in a consistent state (consistent- > as if transactions were executed in some sequential order)

Question 14

What is recovery?

Answer 14

Insure that no data from committed transactions is lost, regardless of any failures.

Question 15

Why is recovery important?

Answer 15

All systems are prone to failures, and handling recovery from failure is a must.

Question 16

Why is redundant data a problem? *

Answer 16

The redundant data problem concerns a piece of data or data fields that is stored in one or more table locations. If the data is updated in one location is must also be updated in tall other locations, so that we know that we’re accessing the correct data. We need to ensure the integrity of the data.

Question 17

How do database systems make it easier to avoid storing redundant data? *

Answer 17

A database system makes it easier to avoid storing redundant data by keeping all the dat in one easily update able location and providing an easy mechanism to do this.

Question 18

What is a data model?

Answer 18

A collection of concepts that can be used to describe the structure of a database.

Question 19

How is a data model used?

Answer 19

Data models are the practical tools used for specifying data abstraction.

Question 20

Define the term database schema.

Answer 20

description of the database

specified during the database design

Question 21

Define the term database state.

Answer 21

The data in the database at a particular moment in time.

Question 22

Define the term data dictionary.

Answer 22

In addition to storing catalog information about schemas and constraints, the data dictionary stores other information, such as design decisions, usage standards, application program descriptions, and user information.

Question 23

Describe the main categories of data models and the differences between them.

Answer 23

High level - ER model - close to the way many users perceive data

implementation data model - Relational Model

low level - physical data models - how data is stored in the computer

Question 24

What is the difference between a database schema and a database state?

Answer 24

• Database schema - the description of the database

- Database state - the data in the database at a particular moment in time

Question 25

What is a database view?

Answer 25

A virtual relation defined as the result of any legal SQL query. The view behaves as if it is not materialized until a query against it is executed.

Question 26

How is a database view used?

Answer 26

Views are used just like other tables. Limits the possible update operations that can be applied to views, but it does not provide any limitations on querying a view.

Question 27

Under what conditions is it NOT a good idea to use a database system for application development?

Answer 27

not likely to change

real time processing requirements

does not require concurrent data access

Question 28

Describe four types of program-data independence and give an example of each.

Answer 28

representation of numeric data: int -> float

representation of character data: fixed length string -> variable length string

units for numeric data: inches -> meters

data materialization (virtual fields): age stored directly or derived from birthdate or current date

structure of stored records: (student, sno, course, coursename_ -> (student, sno, course), (course, coursename)

structure of stored file -> ordered on sno, hashed on sno

Question 29

What are the five major components of the DB implementation architecture?

Answer 29

Scanning & Parsing

Query Optimizaion

Run-Time Environment

Transaction Manager

Access Methods

File System / OS Disk

Question 30

Explain what functions are performed by the scanning & parsing module of a DBS.

Answer 30

translate SQL request into an internal representation (and check syntax & type compatibility)

Question 31

Explain what functions are performed by the query optimization module of a DBS.

Answer 31

select “optimal” access strategy and generate query execution plan

Question 32

Explain what functions are performed by the run-time environment of a DBS.

Answer 32

interprets query execution plan, transactions

query processing

authorization & integrity checks

Question 33

Explain what functions are performed by the access methods of a DBS.

Answer 33

organize information on the disk & retrieve individual records when requested by the run-time environment

Question 34

Explain what functions are performed by the file system, OS & disk of a DBS.

Answer 34

organize disk storage

coordinate transfer of blocks of data to/from memory buffers

Question 35

What is a transaction?

Answer 35

atomic unit of database

processing (commits or aborts)!

Question 36

How does a transaction differ from an execution plan?

Answer 36

execution plan - static

transaction - executing code

Question 37

Explain what functions are performed by the transaction manager.

Answer 37

part of run- time environment

concurrency control: coordinate many simultaneous transactions

recovery: insure that no data from committed transactions is lost, regardless of any failures

Question 38

Why are the functions performed by the transaction manager important?

Answer 38

To ensure data isn’t lost.