The Worlds of Database Systems

Question 1

DBMS

Answer 1

Database Management System

Question 2

database

Answer 2

A collection of data that is managed by a DBMS.

Question 3

schema

Answer 3

logical structure of data

Question 4

relations

Answer 4

data organized as a table

Question 5

SQL stands for?

Answer 5

Structure Query Language

Question 6

XML stands for?

Answer 6

eXtensible Modeling Language

Question 7

What is information integration?

Answer 7

Joining the information of many related databases into a whole.

Question 8

Data Warehouse

Answer 8

Where information from many legacy databases is copied periodically, with the appropriate translation to a central database.

Question 9

DML stands for?

Answer 9

Data Manipulation Language

Question 10

DDL stands for?

Answer 10

Data definition language

Question 11

What does the execution engine do?

Answer 11

The execution engine issues a sequence of requests for small pieces of data, typically records or tuples of a relation, to a resource manager that knows about data files (holding relations), the format and size of records in those files, and index files, which help find elements of data files quickly.

Question 12

Overview of Query Processing

Answer 12

Using DML, interacts with DBMS. Doesn’t affect the schema of database but may change content.

Question 13

Database management system components

Answer 13

Question 14

What does buffer manager do?

Answer 14

Task is to bring approciate portions of data from secondary storage (disk) where it’s kept permanantly, to the main-memeory buffers.

Usually the page or “disk block” is the unit of transfer between buffers and disk.

Partition the available memory into buffers.

Question 15

What is a transaction?

Answer 15

Way that queries and DML are grouped.

A transaction is a unit that must be executed atomically and in isolation from one another.

Any query or modificiation action can be a transaction by itself.

Must be durable.

Question 16

What is durability?

Answer 16

The effect of any completed transaction must be preserved even if the system fails in some way right after completion of the transaction.

Question 17

Two major parts of transaction processor?

Answer 17

1. concurrency-control manager
   * responsible for assuring atomacity and isolation of transactions*
2. logging and recovery manager
   * responsability to preserve durability of transactions*

Question 18

What does storage manager do?

Answer 18

Job is to control the placement of data on desk and it’s movement between disk and main memory.

Keeps track of the location of files on the disk and obtains the block or blocks containing a file on request from the buffer manager.

Question 19

Components of data

Answer 19

1. Data: contents of data itself
2. Metadata: the database schema that describes structure of and constraints on database
3. log records: info about recent changes of the database, supporting durability of the database
4. statistics: info gathered and stored by DBMS
5. indexes: data structures that support effecient access to data

Question 20

ACID Properties of Transaction

Answer 20

‘A’ - “atomicity” – the all-or-nothing execution of transactions

‘C’ “Consistency” - all databases have consistency contraints, or expectations about relationships among data elements. Transactions are expected to preserve the consistency of the database.

‘I’ - “isolation” – the fact that each transaction must appear to be executed as if no other transaction is executing at the same time

‘D’ “durability” - the condition that the effect on the database of a transaction must never be lost, once the tranaction is completed